While the 5.9 Common Rail Cummins is an extremely dependable engine, there are certain things to look out for.

What Breaks When: 2003-2007 Dodge Cummins

Diesel Performance Parts, Diesel Truck Maintenance, Dodge Cummins, Ram, Tips and TricksTags

Written By: Lawrence “LT” Tolman

2003 marked the first year of a new body style pickup for Dodge, and to go along with its new looks, a new engine could also be found under the hood, and the major difference between it and the earlier 5.9 liter Cummins engine (and its Achilles heel) was the addition of common-rail fuel injection. While the 5.9 Cummins is a very robust engine, it does have a few weaknesses that can leave the truck stranded, but nothing that will lead to a catastrophic failure or meltdown. As part of our “What Breaks When” series, this week we’re taking a closer look at the 2003 to 2007 5.9-liter Cummins.

03-04 vs 04½ -07 What’s the Difference?

The 5.9 common-rail is divided into two separate groupings: the earlier 2003-04 models and the later 2004.5 to 2007. While they share most of the same architecture, there are a few key differences which make certain parts not interchangeable, and most of those had to do with fuel delivery. The early 5.9 CR featured an 8-hole injector nozzle with a wide angle spray pattern, and there were two injection events per stroke: pilot (which injects a small amount of fuel to pre-heat the combustion chamber before ignition) and the main injection event, which is where the engine’s power comes from. The pilot injection event is useful since it reduces noise and helps the main combustion event take place, and interestingly enough the addition of pilot injection is why common-rails are so much quieter than the mechanical engines which have only one injection event. The later 04.5 to 07 Cummins 5.9s featured a five-hole nozzle, a narrower spray pattern, and to match that pattern, a different shaped piston bowl needed to be used. In addition, the later 5.9 Cummins also featured a third, post-injection fuel event after the main spray, and the main purpose is to reduce harmful emissions. The third injection event is said to have a slight negative impact on fuel mileage, however with aftermarket tuning, the loss in mileage can be restored.

To ensure your engine lives a long, healthy life, its imperative to keep your injectors in tip-top shape.

On the earlier engine, the wider-angle spray pattern means the piston has to be closer to top dead center when the fuel is introduced, so when tuning there is a limit to how much injection timing and duration you can safely run. On the later trucks, the narrower spray pattern and piston design gives a little more margin of safety and allows for increased injection duration, since the piston will be in the “sweet spot” for more degrees of crankshaft rotation. While there are no inherent strength differences between the two piston designs, you have to be especially careful to monitor EGT on the early design engines.

Fuel System Failures:

Manufacturers found early on if you can inject diesel fuel into an engine at a higher pressure through a small orifice, you can greatly improve how quickly and efficiently the fuel will burn, and also reduce the output of harmful pollutants. In order to operate at pressures approaching 27,000 psi, the pieces inside common-rail injectors need to be machined within a couple microns of each other for proper tolerance. It’s impressive how modern manufacturing can mass-produce such precise and accurate parts, but those tight tolerances and high pressures create an injector which is very sensitive to contamination from water and dirt. If you know anything about diesel fuel, you’ll know it’s not inherently clean, it sometimes contains water, and usually has some dirt in it. If the fuel filters are not regularly changed, there can be a small amount of dirt and moisture that winds up in the injectors, and as a result, early common-rail 5.9’s have a bad rap for faulty fuel injectors, going out somewhere around the 150,000 mile mark. Symptoms can include hard (or no) starting, smoking, knocking, and even fuel in the engine oil. If you are experiencing those issues with your 5.9, chances are you have a failed injector and it’s time to replace them.

If you find yourself in need of new injectors, you have a lot of options. If you are considering turning your truck into a high-performance build, this may be a good time to consider a set of injectors that flows more fuel than stock for some added performance, like a 60hp set from BD. Or, if you just need a stock sized replacement, new Bosch Stock Flow injectors are an affordable and high-quality option to get you back on the road. But either way, be very cautious when ordering sticks for your truck and be absolutely sure of what year engine you have. The injector bodies are the same from ‘03 to ‘07, but remember the nozzles have two different spray patterns. Any 5.9 CR injector will physically install into any head, but if you install an earlier injector into a later engine or vice versa the improper spray angle will cause a rough running engine, excessively high EGT, low power, and likely will cause damage to your engine from the mismatch of components. If you are unsure which model you have, check the tag on the driver’s side of the valve cover for some help. If it’s labeled as a 305hp version, it’s the early, wide spray pattern injector, and if it says 325hp, it’s the later model, narrow pattern injector and piston.

The connector tubes originally found in 6.7 Cummins are finding their way into many 5.9’s due to the fact they completely interchange, last longer, and have better flow characteristics compared to the original 5.9 connector tubes.

And one last note on injectors: any time you replace or remove an injector from the head, it’s a smart move to replace the mating connector tube which comes from outside of the head and delivers high pressure fuel into the injector body. There is a very critical connection between the injector and the tube which is made from two precisely machined surfaces which can easily be disturbed during removal. While I have re-used connector tubes myself, it’s cheap insurance and gives peace of mind to simply replace them as part of an injector change. Plus, you can use the tubes from a 6.7 which have a larger inner diameter to support a little more horsepower if you’re into that sort of thing.

Once you have a brand-new set of injectors, (or if your existing set is still functioning properly) there is a way you can prevent injector failure from contaminated fuel: maintenance. Many new diesel owners are surprised to learn you are supposed to change your fuel filter on a regular basis, and so their truck runs for 30 to 40 thousand miles until the filter clogs and performance suffers. According to Dodge, every 15,000 you should be swapping out the fuel filter, but don’t settle for the cheapest one you can find, since so much is at stake. There are many different options on the market, and each can have a different micron rating, which is a measurement of the size of dirt particle the filter will trap. A great filter for any 5.9 common-rail is the Baldwin 7977. It has a rating of 5 microns, which is the best you can get for a stock filter housing, and it only costs $17 so you can’t really complain about price either. In fact, you should buy two so you can keep a spare on the shelf, since 15,000 miles can go by pretty quickly.

The Rest Of The Fuel System

Once you have the injectors squared away, you can rest easy since the big-ticket item on the fuel system is already taken care of, although there are a few smaller and much less expensive items on the common-rail 5.9’s that will likely fail at some point or another. Thankfully, the Bosch CP3 injection pump is very reliable, however the one user-serviceable item attached to the back of the pump is failure prone. It’s called a Fuel Control Actuator, or FCA for short, but it is also referred to as a regulator. While it ultimately regulates the amount of fuel pressure the pump puts out, it does this by controlling the flow of fuel going into the pump. Whenever there is low fuel demand like at idle and part throttle, a high voltage is applied to the solenoid, and the FCA partially closes, restricting flow, and keeping rail pressure at a lower level. As fuel demand ramps up, less voltage is applied from the ECM, more fuel is allowed to enter the CP3, and as such, fuel pressure raises.

The Fuel Control Actuator takes information from the ECM and essentially tells the CP3 how much fuel to deliver based upon the signals from the ECM.

The FCA is both an electronic and mechanical part, and there are several small moving parts inside which can become stuck or clogged. A faulty FCA can cause a variety of issues, from rough idle, low power, a deviation from desired rail pressure, and even a no-start condition. It’s a pretty common failure, and luckily a new FCA is very easy to install on a Cummins, and it’s also affordable at a hundred and thirty bucks.

One other part on a common-rail 5.9 that’s known to fail would be the Fuel Pressure Relief valve. Whether the valve seat becomes jammed with dirt or the internal spring has failed, the result is a valve that is stuck open and little to no rail pressure, since all the fuel will be returned to the tank. The symptoms are very similar to those of a failed FCA: low power, rough running, or even no-start. Luckily, it’s also very affordable to get a new genuine Bosch FPR valve, and again, the magic number is a hundred thirty bucks.

Unlike GM, Dodge was smart enough to equip their trucks with a lift pump which pulls fuel from the tank and sends it up to the injection pump. As with all best laid plans, the stock lift pump has a reputation for going awry. Early model 5.9’s had an electric lift pump mounted to the side of the engine block, and the later models had the pump in the fuel tank. Since the original block mounted pumps were so unreliable, many early model trucks were adapted by dealerships to run the later style in-tank pump with a retrofit kit, but even the updated in-tank lift pumps weren’t so great. Whenever your stock lift pump fails, I wouldn’t recommend replacing it with another stock pump, especially if you are looking for a bump in power. Instead, you should install higher capacity pump with increased filtration built in, to separate water and dirt, and pull any air out of the fuel. The FASS Titanium Signature Series lift pump will support an elevated power level, but more importantly clean up your fuel, and send nothing but pure, air-free diesel up to your CP3 and injectors. Remember, clean fuel is the most important thing to keeping your injectors living a long and happy life, so a filter and lift pump combo is really an important upgrade for any diesel trick. When ordering a FASS pump for your Cummins, just remember to select the correct option for whether you have a block mounted or in tank stock pump, since the plumbing will be slightly different.

Other Issues

If you don’t consider the fuel system, the 5.9 Cummins is a very reliable engine. The internal parts like the pistons, rods, and crank will last for a zillion miles even with some abuse. The turbos are very responsive and will give a long service life, but they don’t have a tremendous horsepower potential. Other than small wear and tear items like the water pump and belts and hoses, you can expect a lifetime of use from a 5.9 without doing anything more than basic maintenance. But that doesn’t mean there isn’t any room for improvement.If you don’t consider the fuel system, the 5.9 Cummins is a very reliable engine. The internal parts like the pistons, rods, and crank will last for a zillion miles even with some abuse. The turbos are very responsive and will give a long service life, but they don’t have a tremendous horsepower potential. Other than small wear and tear items like the water pump and belts and hoses, you can expect a lifetime of use from a 5.9 without doing anything more than basic maintenance. But that doesn’t mean there isn’t any room for improvement.

One disadvantage of an inline engine is coolant flow is somewhat limited near the rear of the engine. Since number six is at the end of the line, the coolant circulates around the rear sleeve much slower, allowing more heat to be built up, so if a heat related failure does occur (from aggressive tuning or ignoring high EGT), its usually found on the rear most cylinder. For a long time, that was just a fact of life, but now a Coolant Bypass kit from Fleece is the solution. It allows you to tap into a freeze plug on the rear of the engine, and provides a path for the warm coolant from the rear cylinder to flow right up front to the thermostat, which evens out the temperature across the block, and relieves pressure that can build up in the cooling system from excessive heat.

By having an equal distribution of coolant flow to the rear cylinders of your Cummins engine, you can safeguard against excessive heat developing at number 5 and 6 especially.

Speaking of heat, one part of the intake system on a Cummins that is the most restrictive is the intake horn. The stock part was designed to be about as aerodynamic as a brick, and the inside resembles a drinking straw. As we’ve discussed many times before, a restrictive induction system can lead to increased heat in the engine which could decrease longevity and fuel mileage, and this is no different on the Cummins. A few simple parts like a cold air intake, Monster Ram intake horn, free-flowing exhaust, and a cold air intake will together improve power and fuel efficiency, and lower the temperature of the exhaust gasses, all of which are great for your Cummins diesel.

Not As Bad As It Sounds…

By anybody’s standard, the 5.9 liter common-rail Cummins is a great engine and will give its larger displacement rivals a run for their money. There were a few teething problems, and the first CR Cummins did have a few inconvenient problems, but nothing that can’t be fixed with readily available parts and tools. And as long as you keep up on your filters and scheduled maintenance, you should expect several hundred thousand miles of trouble-free operation, no matter what path you take on your build. We’ll get into high-performance options another time, but the 5.9 can be built to be a heavy-hauling tow rig, a fuel sipping daily driver, or a fire breathing 1,500hp monster, and the best part is the inline design also makes them the easiest diesel engine to work on from the Big Three. Plus, if you drive one with the tow mirrors flipped up, you can earn one of those giant “C” decals to place in your back window…

66 thoughts on “What Breaks When: 2003-2007 Dodge Cummins

  1. Solid write-up, Josh! I considered myself savvy in my early 03 HO Cummins and this article showed me how little I actually know about the motor. Thanks for the straight-to-the-point, well written article.

  2. Very informative. Recently purchased Dodge 05 2500 (82,000 miles) and would like to “get ahead” of the downfalls of this years 5.9L. I have read on multiple sites on the injector and fuel pump issues but your site is the first that mentioned about the simpler parts (FCA and FPR) that contribute to the 5.9L problems. Appreciate the article.

  3. Although my 2003 5.9 has never run out of diesel, I came close once and wondered if it would be in need of bleeding system. Anyone know? Thanks

    1. Hi there, and thanks for the question. Yes, you’d definitely need to prime the system if you run it out of fuel, to include cracking the injector lines to bleed the air out. In most cases, depending on your lift pump location (which can alter the exact method), you’ll want to remove the line after the lift pump, bump the key until you can get fuel at that point, then you’ll need to crack all six injector lines, continue to bump the throttle until fuel comes to the first line, close that one, and continue until you get to at least the fourth back injector line. Once you’re at number four, you can usually get away with closing the remaining two and the truck will fire. Hope this helps!

  4. Hey just wondering what people’s thoughts on this truck im considering purchasing. Its an Auto 04 dodge 2500 early Cummins with 430000km . Just all basic maintenance records none of which include fuel injectors and any other major repairs.
    Its 5k cad . Just wanted some others thoughts on this purchase. Thanx

    1. Hi there. Coincidentally enough, that’s the same truck I (Josh) personally own, early ’04 Cummins. With that amount of miles, there will definitely be a few things that will need to be addressed if they haven’t done so already. At the minimum, you’re probably due for injectors and new connector tubes, as you’ve mentioned. Further, the transmission is more than likely due for a refresh, torque converter and clutches at the minimum. Also, if the truck still has the factory fuel filter mounted lift pump, its probably ready to be replaced at this point. Beyond there, more than likely the turbo probably has excessive shaft play and going to need to be replaced. Overall, for $5k, that’s a great price, but you’ll be needing to invest some of the savings back into it, so if you’re ready for a little project, do it. Personally, the 03-04 trucks are my preferred year range that are highly capable and reliable, but with a quarter million miles on it, there are absolutely items that are ready to fail. Lastly, I would presume the front end must have had some repairs to it, but if not, a gear box, tie rods, and ball joints are in your near future, as well.

  5. Great write up! I’ve got a 05 (4.5) 3500, QCSRW, 5600NVG (man), with 161,000 mi, Edge CTS2 Evolution, Banks intercooler and intake system, 4″ turbo back (CAT del) with flow pro muffler and backyard modified air intake box. My stage 3 upgrades are lift pump and air intake. My stage 4 upgrades I think will be turbo and exhaust manifold. I was looking for info on CP3s to try and figure out fuel delivery requirements. This article hit on so many areas regarding fuel delivery (I change my sticker filter every 5000 mi with my oil and fuel additive, maybe overkill 🤔 oh well). The part about the FCA was what I needed to know. From what I’ve read the FAAS is continuous fuel pressure delivery while the Airdog is an “on demand” capable of up to 155ish. So why would I need potential “lags” and possible breakdown points in my fuel delivery when the FCA is already controlling fuel to my CP3. I also appreciated to part about the coolant bypass, that will be part of my stage 5 mods (injectors, head studs and now coolant bypass). My endstate, I own it, I can’t afford a newer diesel at almost $60-70000 (really don’t want the freagin payment) and I want the million mile cummins! Thanks again, great read! Any responses appreciated. Danny

    1. And thanks for the thorough response. Also to note, well done on the upgraded intercooler. Especially if your truck is in fact a 2005, that was the one and only year that Cummins/Ram decided to put in a factory intercooler with plastic end tanks (very bad idea). In regards to your question about the fuel pressure, you are correct that the FCA is responsible for controlling the output pressure of the CP3 after its turned into high pressure. The AirDog “Demand Flow” essentially works to only deliver roughly as much fuel as can be consumed by the CP3, so when less is needed, it delivers more, but this also means that the lift pump can change the output routinely. Plus, you have returns in place to return fuel. That said, even with an AirDog, all returns are necessary because there is simply no way to actually only deliver, under all circumstances, the exact amount of pressure. Glad we could help provide some useful information for you in the article, and if you’ve got any other lingering questions, feel free to reach out and we’d be happy to help.

  6. Hello Josh hope all is well with you and your family in these times, and thank you for this write up. I’m in Vancouver B.C. Canada right above you so not far from you guys.
    I just purchased a 2005 Ram 3500 Laramie 5.9 of course, that was imported from Arizona. It has 162,000 miles.
    I know this is a bit to ask but, I am only interested in reliability, longevity and fuel economy. I’m satisfied with the power so not interested in going that route but understand you just get a little more when you make it breath easier etc.
    Now for the ask part. Could you please email me or list what upgrades, part exchanges etc that I should do for my specific goals.

    Thank you in advance
    Kind Regards

    1. Hey there, Rob, thanks so much for the inquiry, and no, you’re not that far from us at all! Sounds like you picked up a gem, I’m personally currently driving an early 2004 Cummins, and yes, there are definitely ways to squeeze some extra MPG’s out of it. Historically, the 2004.5 and 2005 model years didn’t get quite the fuel economy as the 2003-2004 or the 2006-2007 due in some part to the change to the updated injectors in 2004.5, but predated the latest ECM in 2006. That said, you’re absolutely correct, upgrading the airflow (I like the S&B cold air intake) and honestly timing/fueling via programming (which inherently will also increase power) will net you additional fuel economy, and for this I’m a fan of the Smarty Jr. programmer. Then, run a quality synthetic oil (I run Schaeffer’s) and a good fuel additive that increases cetane (such as F-Bomb Hellfire), and you’re bound for success. From there, making sure you have the most common 3.73 gears, and not the optional 4.10’s, and you’re on a road to success. And just because I ALWAYS tell everyone that has a 2005, keep an eye on your intercooler. It was the one and only year that Ram thought it would be a good idea to use an intercooler with plastic end tanks instead of metal…..totally absurd. Anyways, we’ll shoot you an e-mail and can go from there, congrats!!!

    1. Especially if this is an early 2007 with the 5.9, and not a 2007.5 with the 6.7L, and if it really does still have the factory/original injectors, yes, it will most likely need injectors unless its a rare anomaly that had nothing but the cleanest of fuel its entire life.

    1. Hi there, thanks for the question. If you’re asking about lack of fuel rail pressure, that depends ultimately on the reasoning for the lack of pressure. Most often, though, its due to a failed or failing pressure relief valve, which is located on the top of the rail. One method if yours is failing is to replace with a new relief valve. However, if you’re looking to eliminate the issue once and for all, then you can install a pressure relief valve block off. The caveat to this is that especially if you’re running any aftermarket performance tuning that increases rail pressure, then all of that pressure will be going directly to the injectors which can lead to premature failure. We’d recommend first diagnosing what is causing the lack of rail pressure, again, assuming that’s what you’re specifically asking about, then replacing as necessary.

      Stock Pressure Relief Valve: https://www.dieselpowerproducts.com/bosch-f00r000632-valve-03-07-cummins
      Pressure Relief Valve Block Off: https://www.dieselpowerproducts.com/p-7759-industrial-injection-pressure-relief-valve-block-off-03-07-cummins.aspx

  7. Great article Josh. I will bookmark this one for review from time to time.
    I recently purchased a 2007 RAM 2500 miles. It was a 2 owner truck that has 217,000 miles on the clock and came with a stack of maintenance records. Review of the records indicate oil changes every 7,000 miles and receipts for a number of fuel filters but no mileage was indicated for their installation. Your reply to one of the previous questions indicated I should expect the injectors to fail and need replacing. Does one have to change them all at one time or can you change them as they fail? Is there a financial advantage to changing them all at once verse independently?

    1. Hi there, thanks for the question, and congratulations on the new-to-you truck. First and foremost, I’m presuming your truck is an EARLY 2007, as oppose to a LATE 2007 (2007.5) as that would be a 6.7L, as opposed to a 5.9L. First, we can presume the fuel filter was changed recently based upon the stack of records you received, but I wouldn’t presume something so imperative, and since fuel filters are so inexpensive, you may as well put a new one in for peace of mind and to start YOUR service records. I personally use the Baldwin PF7977 in my personal truck, shown here:


      In regards to the injectors, it definitely would not hurt to have a return rate test done so you know where you’re at. That said, normal symptoms would be some white smoke, especially at idle, and that it will turn over a few times before firing, especially when the engine and ambient air temperature is cold. If the injectors have never been replaced and its found you have one or two that are returning an excessive amount, you really should replace all of them as the balance rates between those and the original injectors will differ significantly. Further, when replacing the injectors, its a VERY good idea to change out the injector connector tubes, which connect the injector lines on the outside of the head to the injectors themselves (basically a horizontal sleeve). Further, the original connector tubes have been superseded to the same ones used in the 6.7 Cummins, which have a slightly larger inside diameter (I.D.), further exacerbating the balance issue. We describe a lot of the fuel related issues of the 2003-2007 Cummins in this blog, as well:


      Beyond that it would mechanically make sense to replace all six injectors, there’s also a cost savings if you’re paying for the labor as once the valve cover comes off, you’ve already started the process needed to replace any of the injectors. Besides the connector tubes being updated, Bosch (company that makes all of these fuel system components) has also made several revisions from the original “505” injectors as they’re known over the years to increase their dependability.

      Hope this answers your questions, good luck, and if you have any other questions, please let us know.

  8. Hey Josh, just wanna start off saying, “What an absolutely amazing and very informative write up you gave!!” Honestly thankful for everything you mentioned in this. Now more so I need some information about my 2004.5 Cummins dually with the auto tranny. I bought the truck from a dealership back on November 5, 2019 with 156k miles on it. I now to date have 208, 368 miles on the truck. Overall the truck has been a complete blessing compared to my 6.4 Powerstroke. (Even tho my Powerstroke is my favorite when it comes to “play” and power) anyways to try and stay on topic, back in beginning to middle of summer this year I noticed after hauling dump trailer home loaded with tools, and as I was backing down the driveway and put the truck into Park….at idle the truck had a distinctive, and constant ticking(?) knocking(?) like a metallic tapping(?) sound coming from what sounds to be the driver side. Can hear it plain as day with the windows down or outside the truck but I personally can hear it when inside the truck with windows up as well. As soon as I put the truck into park tho, the noise stops for a quick 2-3 seconds before it starts again. Did some research but tracking this sound down is literally like looking for a needle in a hay stack.

    For a lil more “food for thought” to maybe help you, help me.. if outside the truck the sound I’m hearing is more pronounced either at the driver side front wheel well, or (and as confusing as it sounds) the other location I’m feeling like I’m really hearing this sound is coming from like underneath the tranny. I have done a tranny filter and fluid change on the tranny, I do my oil changes every 5-7k miles and do the fuel filters at the same time. I have the Fass 150HD system on my truck currently as well. I have yet to replace the injectors but have replaced the FPR and the FCA. I have adjusted the valves (intake to .010 and exhaust to .020) I even did the band adjustment for the tranny (inside pan) when I did the tranny service. I was told this sound could be anything from a leaking injector(s) to being loose torque converter bolts, could be a bent rod or even a harmonic balancer outta whack. I was told it could also be the fan clutch or an exhaust leak due to that’s the only thing I can best describe this sound as. I did notice that number 6 manifold port, manifold gasket is ripped/making a exhaust leak but honestly I don’t feel like that’s the issue due to the passenger side you hardly hear this noise.

    Want to apologize in advance for this huge, and long comment but I’m really just at wits end with this noise and just going to start thinking that it’s normal like everyone else seems to just start doing on all these dodge, Cummins forms that I’ve been researching. I figured the most details and the best way I can explain it gives me the best chances for you to maybe be able to help me out on getting this noise figured out and hopefully resolved. Will just add that if you’d like a sound clip even, send me a email so i know how to get ahold of you and I’ll be sure to get a clip over to you ASAP!!


    1. Buddy,
      Actually, thanks for the detailed description as that obviously helps diagnose an issue. Honestly, I’d say injectors. After reading your question a couple of times myself and thinking “injectors,” I also sent the issue to one of our other guys, and that’s his first guess, as well. Sure, everything you’ve mentioned “could” be making similar noises, but based upon the mileage of the truck, that particular model year range of truck (2004.5-2007 which used what’s called the 505 injectors, and are known for failing around 100-150k at least), how you’re describing the sound and its location, all spells injectors more likely than other causes. Sure, you could have loose flexplate bolts, but its not as likely. Sure, you could have rod bearings going out and the sudden shift in RPM due to the change from Drive or Reverse to park causes the additional movement….but its not as likely. Overall, I’d recommend testing the injectors and if they need replaced, do all six along with the connector tubes. You could run the injector return test as described to give you a clue if that may be the issue. That said, the “clicking” noise you do hear when it changes RPM/gear selection could be due to that sudden change in RPM and load. Long story short, injectors would be the first thing we’d recommend to diagnose. If that’s not the issue, we can keep working through the issues. Good luck!

  9. For Buddy Young’s question (10/16) and Josh’s response (10/20). The “tapping” your describing could be your CP3 injection pump making noise. It’s more of a tap then injector tick or knock (marble bouncing around is a good description). I consider new injectors preventative maintenance so good advise to look into them. Just want to throw out the CP3 idea. I have dealt with and cured most the cummins noises throughout the life of my 03. When I read the question I was thinking CP3. I hear it on 50% of these trucks but its nothing harmful and usually comes and goes. You can pull the gear, bar the engine over, and reinstall gear to pin point the problem but it usually comes back. Good luck, nice to see advice shared so readily. It didn’t used to be that way. Take Care.

    1. Good point and you’re definitely correct that the CP3 could be making that noise and its definitely more of a tapping type of noise. Thanks so much for chiming in with your experience, ALWAYS appreciated!

  10. Hello Josh, great write up thank you. I just purchased my first diesel truck. It’s a 2007 Ram 2500 with the 5.9L and 121,250 miles. One owner, no rust, beauty of a beast, really stoked. Like I mentioned, it’s my first diesel and know next to nothing about proper maintenance and servicing on a diesel. It runs great but only thing is I know nothing about the service history. Wondering if you could either email me back a good strategy to start MY servicing or comment back your thoughts on what I should do. Also wondering about a fuel additive and when to add (every fuel up?). Thank you, much appreciated

    1. How cow, sounds like you found an absolute GEM! You definitely knew exactly what you were looking for based upon the description, nicely done. Purchasing a used truck can be difficult due to exactly what you describe, not having a good service history of the vehicle. To get started, I’d say that you have three options, and two of them are better than one:
      1.) You can presume that the truck has been adequately serviced (transmission, axles, engine oil, etc.) and go off of the service schedule in your owner’s manual (there will be a schedule A and B, and if I remember correctly for your truck, schedule B outlines what most would consider normal use). At that point, the drivetrain’s lubricants and any filters (transmission) would have been serviced every 30k, which means you’re right there needing a service anyways, or that it was just done. Personally, I don’t like to presume anything, so I’d throw this option right out the window.
      2.) Find a reputable local mechanic and have them go through everything on the truck, to include testing all of the oil, check u-joints, look for any metal material in the transmission pan, and change anything they see.
      3.) Change all of the fluids and filters as soon as you’re able and get your own service record going (this is the best option in my opinion). For this, you’re going to probably spend a few weekends here and there changing various fluids on the truck and paying special attention to all of the fluid that comes out, looking for any metal shavings, or any abnormalities. You’ll be changing the engine oil, transmission, axles, fuel filter, etc. I personally use and highly recommend Schaeffer’s brand synthetic oil all the way around. Its more expensive than conventional oil, but its good insurance honestly. Further, we can “presume” the valves have been adjusted at 100k, but no guarantee, so there again, you’ll want to either learn to do this yourself or find someone to do it for you. In instances like what you’re in, being a diesel newbie so to speak, its good to get your feet wet on a lot of the projects, and then maybe lean on a local mechanic to help you out with some of the bigger tasks, but that’s up to you. It wouldn’t be a bad idea to have the injector return rates tested to know how much life you’ve got left in them.

      Now, in terms of a good quality fuel additive, absolutely yes. I would personally recommend F-Bomb Diesel Additive, its what I run in my own truck and it works great for all of the reasons it should. Check it out here:


      And here’s a link to a Schaeffer’s oil change kit:


      Plus the rest of the Schaeffer’s products I recommend here:


      Hope this helps, and if you have any other questions, feel free to give us a call or even shoot an e-mail to [email protected] and we’d be happy to help.

  11. Josh, great article and finding it was perfect timing. I just put in a new (reman) DFC engine into my 2004.5 3500 after a catastrophic failure (hole in side of block the size of a beer can). I finally got every thing together and got it started after bleeding the fuel rail. it was running a bit rough initially and found another fuel leak on the #6 injector line. It started running smooth then just died. Started checking for other leaks and found the Fuel Pressure relief valve was hot to the touch,. I assume it was caused by the friction of relieving the pressure but don’t know for sure. The engine will no longer start and after reading your article, I am about to buy a FPR and a FCA unless you have other ideas?

    Thank you for helping all of us that graduated from BYMU (Back Yard Mechanic University)

    1. Thanks for taking the time to read the blog! It definitely sounds like a fuel related issue if you were able to get it fired off, then died, and not surprising with a full engine replacement, honestly. Obviously, I’m not sure if you also got a new CP3, or any of associated fuel related parts with the DFC engine, presuming not. The fact that the PRV was hot could have something to do with it, potentially relieving excess rail pressure and you’re 100% on the right track to replace the FCA and PRV as those are both huge culprits in a no start situation. In fact, I’ll do you one better and recommend you read the below blog that goes step by step on how to diagnose a no-start on your truck, mostly looking at the fuel side of things. Give it a good read, its helped a LOT of people diagnosing the same situation, or similar, as to what you’re dealing with: https://www.dieselpowerproducts.com/blog/2003-2007-cummins-no-start-no-problem/

  12. “CR Cummins is reliable”
    Reading this while looking at the 05 that’s been in the shop more than one the road in since I bought it in 17, once for an ecm and the rest of the time fuel issues. Or the blown cp3 in Detroit. The first set of injectors in florida, second set 5 months later in Texas, 3rd set 2 weeks later at Home, 4th set in Lake Houghton MI, 5th set at home, about to get its 6th set and 3rd set of tubes, once again by a shop……. idk, something something reliability? I guess that’s why I’m selling the 05 the second it’s out of the shop and currently driving a nv5600 swapped 12v

    1. While I’d completely agree that the original “505” injectors in the 2004.5-2007 Cummins were inherently failure prone, Bosch revised the design of these injectors that substantially increased the life expectancy years ago, so honestly its pretty surprising the failure rate you’re seeing. Of course, sounds like you’re putting on quite a few miles with the various places the truck is getting injectors, but nevertheless, still odd to me. I can only presume the injectors being installed are of high quality as we have seen some pretty shady remanufactured units coming from various suppliers we won’t mention, but one would think at least one of these sets would be good. Are you doing anything “out of the norm” such as using 2 stroke oil in your fuel (common old school practice), running WVO (waste vegetable oil), any particular chip/programmer you’re running that increases rail pressure? If so, what is it and have you monitored fuel rail pressure? Are you running a pressure relief valve block off? Sorry, lots of questions but there can be numerous factors that could be leading to your unusually high failure rate. Nevertheless, you can count that your 12 valve injectors won’t be failing you!

  13. Hi.
    I have an 06 2500 auto and issues are starting. doing some research and came across your advice regarding injectors. My last oil change and regular filters etc i mentioned hearing an unusual tick. mechanic said he couldnt hear it. well it got louder turned into what i would call a knock. some light searching suggests injectors clogging. so i put some cleaner in and fresh fuel. on my return trip, 20 mins or so, the throttle starting sticking. And byt thw time i returned i had to shut down just to take out of gear for fear my rpms would skyrocket. Ive called my dealer they think i should have it towed to them. waiting to hear back from my regular, trustworthy, mechanic whom i’ve been going to for every vehicle for 20 yrs. very good diagnostic skills. but he admits he has had to repair very few cummins. fords yes he has been in many.
    So im asking your thoughts. I have 175k do regular filters etc but never injectors. i do have a new turbo on my work bench, stock waste gate went etc. so could that have caused injector failure or is it just time.

    Thank you

    1. What you’re describing definitely sounds like injector issues. The ticking is typical of when the injectors begin to fail, symptomatic of an improper spray angle so not all of the fuel is able to atomize within the piston bowl. Then the increased / hanging RPM’s sounds like one of your injectors is sticking. Definitely in no way that you’re getting ready to replace the turbo impact the injectors, its merely time, and honestly, at 175k if you haven’t done them yet, you’ve done pretty well. Fortunately, Bosch (original manufacturer of the injectors) superseded the original design to a more robust unit that is even less likely to fail years ago. If you’re not looking to increase power and looking for a quality set, I’d recommend going with a set of genuine Bosch remans and a new set of Bosch connector tubes. You’ll want to replace all six and your truck should be running good as new. Here’s a couple of links to specifically what I’m recommending:


      Good luck with the repairs, and if you have any other questions, don’t hesitate to reach out.

  14. I’ve got an 03 with 264k and climbing. I’ve recently had an issue of hard hot start and high lopey idle. I’ve seen this before on an 04 I had 10+ years ago but couldn’t remember what it was. Your write up just gave me an “oh yeah, I remember now” moment. 😁 Just ordered a new FCA. That should get me squared away for another 264k miles.

    1. Thank you. The quickest and easiest method is to hop under the truck and see if it has a catalytic converter. An early 2004 would not have a factory catalytic converter (unless its a California specific model), and all 2004.5 models would have come from the factory with a catalytic converter. Another step would be to check the engine tag on the valve cover. If the rated horsepower is 305, then its an early 2004, if its 325, then its a 2004.5. And finally, you can check the build date on the door jam. If it was built pre-2004, then its an early 2004, if built 2004+, then its a 2004.5.

  15. Hi Josh. I have a 04.5 2500, 240k miles. Noticed my Cp3 has a drip coming from the back side. Been doing some reading and the most likely issue I’ve found is that the O-rings on the fuel pump part of the unit may need replaced. Does this sound likely to you? Thank you for your time

    1. Hi there, and thanks for the question. I’m looking to clarify: when you say its leaking on the back of the fuel pump part, are you saying that its leaking on the back side of the gear pump, as in between the gear pump and the CP3 housing? Here’s a picture of the gear pump so you know exactly what I’m talking about:


      But maybe to answer both possible questions, yes, there are o-rings on each. For the seal between the gear pump and the CP3 housing, there is an o-ring that almost looks like three circles, but all one piece. In regards to the CP3 itself, there is an o-ring at the shaft itself. Hopefully its merely an o-ring to get you back on the road, but if its not, at 240k, if the pump has yet to be replaced, it may be in need to change it out. Here’s a link to a complete factory Bosch unit:


  16. Hey Josh, I really enjoyed reading your article. It was insightful and will be helpful with preventative maintenance on my trucks. With that being said, I have a question on one of my trucks. I have a 2006 2500 mega cab Cummins with a 48re and 300k miles. It used to get 20-22 mpgs easily highway or city but over the years it has dropped to around 12 or 13 no matter the road conditions or speed I drive it. On top of that, the truck has started to smoke more. Even taking off from a stop sign under light throttle it will smoke black, unlike in the past. It has stock sized tires, no tuner, transmission shifts fine (just replaced the transducer and upgraded to a GM shift solenoid), pulls and drives great and idles smooth. The injectors have already been replaced at least once, could it be I need another set? Would this help with the fuel mileage and excess smoke? or could it possibly be I need a new fuel control actuator?

    I’ve done a lot of research but haven’t been able to find any answers. Any advice would be greatly appreciated. Thanks again.

    1. Hi there and thanks for the question and thorough explanation of what’s going on. First, I don’t feel the FCA could be causing this, that would typically be more attributed with a hard start or no start situation, but since your truck is seemingly running “fine,” I’d say that’s not the culprit. First, and to point out the obvious, you have a bad fuel/air mixture which is most likely causing the issue, now the hard part is determining what is causing this. So, you’re absolutely correct in that the injectors could be causing both the MPG and smoke issues. Since you have 300K on the truck, it could be time to replace them again or if they were replaced with a remanufactured unit that I’ll just say isn’t the best option, then that could be the case. The factory design of those injectors were upgraded long ago due to notorious failure rate issues with them. Bosch, the original manufacturer of the injectors does a great job of the reman process, or you can also opt for brand new from Bosch. Plus, there’s a slew of companies that make upgraded injectors to deliver more horsepower. Here’s a link to the Bosch remans that have proven very reliable for us:


      But honestly, since the truck is starting fine, I can’t imagine that bad injectors would cause MPG’s to drop that far and you’d be seeing more white smoke than black smoke, so….moving on!

      The more I think about it, I’m leaning more towards a lack of air flow or air flow inefficiencies, and maybe even something causing a “drag” on the engine. Lets first start with air flow. First and foremost, you mention the truck is basically stock. Do you have an aftermarket cold air intake? Either way, make sure your air filter is clean. While you’re at it, pull off the boot on the front of the turbo and check for any shaft play at the compressor wheel. Do you see any damage to the fins or scratches on the housing from the wheel rubbing/striking the inlet? At 300k, you’re probably due to replace the turbo and even the cartridge that the shaft spins on could be worn, which replacing the entire turbo would take care of.

      Another actually simple cause to both issues and a likely cause are the intercooler boots (four in total; one at the turbo, one on each end of the intercooler and another at the intake manifold) and intercooler itself. The factory rubber boots can crack and cause a significant loss of air pressure. Unfortunately, simply inspecting them doesn’t do the job, you have to pressurize them to really see where they’re leaking. The simplest method is to build a cap that covers your turbo with a cap and a port for an air compressor and an inline pressure regulator. This will allow you to pressurize your system to say 30 pounds of “boost” and really see where leaks could be happening at. DuramaxTuner.com also sells a kit they’ve put together if you don’t want to build one; here’s a link: https://duramaxtuner.com/turbo-chargers/stealth-series/boost-tester.html. If your boots are in good shape, it would be privy of you to also remove the intercooler and radiator and thoroughly clean them. Your engine works efficiently on clean and cool air, but if the intercooler can’t properly cool the air because the fins are clogged up with dirt and bugs, you’re shoving hot uncompressed air into your engine, again, causing both issues.

      Here’s a link to all of the options we carry for replacement intercooler boots, intercoolers, and radiators:


      And finally back to the fueling side of the equation, below is a very thorough explanation of diagnosing a no-start issue on a Cummins. While your truck is starting fine, it goes into detail on how to diagnose various fueling related issues that could be applicable, but again, I’m leaning more on the side of airflow based upon what you’ve told me.


      I hope this information helps and good luck. If you have any other questions or run some tests and have results to report back, please respond.

  17. 2004 5.9 150k miles ticking noise. I hear what sounds like metal to metal ticking from top end. Put a wooden stick to my ear to each injector and they kind of sound like what I am hearing. Never had the valves adjusted but am considering having that done. Many people on y tube say it might be a loose clamp on injector hold down clamp? They are all tight. Damn injectors are $$$$!
    You’re thoughts are appreciated.

    1. At 150k miles, you’re due for a valve adjustment as those should be every 100k miles. That said, its more than likely your injectors, especially if the truck is actually a 2004.5 model year as opposed to an early 2004. The 2004.5-2007’s have what is known as a 505 injector, which merely is referring to the original Bosch part number of 0986435505 as opposed to the 2003 through early 2004’s that have a 0986435503 injector. If the injectors haven’t been replaced, and presuming they have not been yet, the original design had a relatively high failure rate. Fortunately, Bosch recognized this issue and updated the injectors that are available today for a replacement. To be certain, you could have a return rate test performed on the injectors. As the injectors continue to wear, if that is the issue, the truck will turn over a few times before firing, especially when the engine and ambient air temperature drop, you’ll get a small puff of white smoke at idle, and a bit of a rough idle. If the injectors are in need of replacement, I’d recommend going with a set of genuine Bosch plus a new set of connector tubes.

      Here are the injectors for the 2003 – early 2004:

      And here are the 2004.5 – 2007:

      And finally the connector tubes:

  18. Josh,
    No question here…yet. Just had to comment though, this is the most informative, well written post I’ve read in a long time. Comments and responses are also beneficial, I read the whole dang thing. This post has legs too, started in 2019 and still going strong two years later, that’s awesome. Professional, respectful, knowledgeable responses, when I purchase replacement injectors you can bet it will be from one of the links on this now bookmarked page. Plus the grammar and spelling are correct (they do matter, especially when discussing topics like 5.9L Cummins common rail, automatic transmission valve bodies, or quantum physics), your English teachers would be proud. Thanks again for taking the time to help others.

  19. I have a 2003 6 sp man that had a bad engine knock. replaced with a 2006 using the 2003 ECU and wiring harness, 2006 engine is now in truck, cranks no start. Fuel pump ok but no voltage to it, no fuel level on the IC. I may have to put the 2006 ECU on the 2006 engine (updated fuel and boost tables apparently) but I cannot find connector pinouts for the two big ones going back to the the body (on top of the transmission). suggestions on where I can get those? would like to get this done and fully repsonsive.


    1. Hi there, Richard. Yes, there’s enough differences in the 2006 engine compared to the 2003 ECU that electronically, the engine needs to be handled by either a custom programmed 2003 ECU, or a 2006 ECU. For example, the 2006 engine has different injectors and pistons compared to the 2003, and those injectors are meant to fire 7 times per event if I remember correctly versus 5 times. The wastegate on the 2003 is mechanical versus electronic on the 2006. If your lift pump was original on the 2003 it was mounted on the engine, but it is in-tank on a 2006 vehicle, but maybe you have already accommodated for this by installing a separate in-line pump. Then, if you were to install the ECU out of the 2006 and install into the 2003, there’s issues with compatibility for other things on the truck, but thankfully you have a manual trans that will help with that. Overall, I’m not aware of a simple fix for this and believe you will need custom tuning and potentially a custom wiring harness to make this work. There’s a couple of companies that come to mind that I believe have helped in these situations. I would recommend contacting either Breakout Tuning or Hardway Performance.

  20. I question yet. Like so many on here I am a fan and just wanted to say thank you for the article.

    Getting FCA replaced but it’s costing $800 to have a local shop in San Diego do it the 800 includes the diagnostic check. I will be upgrading to FASS myself soon and with 340000 miles on my 2003 HO will most likely need to replace injectors soon as well yeah.
    Thanks again.

    1. No problem, we’re here to help! $800 to replace the FCA? I wonder how much diagnostic they’re going to be doing. Typically, FCA replacement is billed at one hour labor (at most) and then a one hour diagnostic fee. While I’m guessing they are selling the part for more than we are….we currently sell a genuine Bosch for your application for $131.80, so even if you are paying $150 labor rate for two hours total, that’s $431.80, about half the cost of what you’re being quoted. The FCA is VERY simple to swap out. There are three Torx screws and one electrical connection. The big thing you need to make absolutely sure of, is that when you pop the FCA out, before you do, put a rag underneath because there is a “ball valve” in the hole, looks like a tiny ball bearing, and it can roll out and you’d never find it again. If it does come out during removal, no problem, just set it on the end of the FCA that goes back into the pump (sometimes a light coat of grease is necessary so it doesn’t roll off), then slide the FCA back into the CP3 pump, reinstall the three screws, plug it in, and you’re good to go. Here’s a link to the FCA I was mentioning: https://www.dieselpowerproducts.com/bosch-fuel-actuator-03-07-cummins

  21. No question yet. Like so many on here I am also a fan and just want to say Thank you for the article.

    Getting FCA replaced but it’s costing $800 to have a local shop in San Diego do it the 800 includes the diagnostic check. I will be upgrading to FASS myself soon and with 340k miles on my 2003 HO i will most likely need to replace injectors soon as well.
    Thanks again.

    1. Thanks so much for taking the time to read and glad our articles can help. If you’re pretty certain that the FCA is in need of replacement, you could save a TON of money by doing the job yourself. We sell the FCA for a 2003-2007 Cummins for about $130 and its a very simple swap, literally three bolts and one electrical connection on the CP3.


      And if you’re not sure, here’s another article we wrote about diagnosing fuel related issues on the same truck, maybe it will help you save some money:


  22. Very informative and educational read thank you for that. However I still haven’t been able to completely diagnose my issues that started a few years back and have just been off and on constantly. First of all my air dog went out so while i was waiting on shipment of the new one my cp3 was doing all the work sucking the fuel right through the non working airdogs filters. Could that possibly have put some significant wear on the cp3? The issues I’m having now is I just installed all reman 90 hp injectors and adjusted the valve lash across the board runs better than it has in a long time. Just the last couple times I started it it would randomly ramp up to 25kpsi then drop back down to around 3. It even completely stalled out at one point. After it’s warmed up it seems to run fine. Now when I’m driving it and get on it pretty good with the new injectors the rail pressure seems to drop more than it should. I keep swapping the two fcas I have trying to decide which one of the two works better or maybe they are both bad? Or could it be possible the cp3 is worn to the point where it can no longer keep up with the demand?

    1. Thank you for taking the time to read our article and glad that it could help you to some degree. You were right to swap out the fuel control actuator once the rail pressure started to randomly spike as that’s the component that is responsible for metering rail pressure, taking the commands from the ECM. While there could be other factors, such as a damaged wiring harness going to the FCA, being that you did run without an operational lift pump for some time, it is likely that the CP3 itself was damaged and is now bypassing fuel, ramping up rail pressure. Its not very likely that you have two bad FCA’s, so personally, my next move would be to just verify the wiring harness to the FCA, then if that appears good, to replace the CP3 itself.

      Here’s another article that is somewhat related to your issues that may be of relevance, at least in testing parts of your fuel system: https://www.dieselpowerproducts.com/blog/2003-2007-cummins-no-start-no-problem/
      And here’s a genuine Bosch replacement CP3 that I’d recommend: https://www.dieselpowerproducts.com/bosch-cp3-injection-pump-03-07-cummins

  23. Great article Josh. Was just wondering if you ever use any type of fuel additive?
    I use seafoam and power service diesel kleen +cetane boost in the spring, summer & fall, & seafoam & power service diesel fuel supplement +cetane boost winterizing/ antigel in the winter.
    Thank you.

    1. Thank you for taking the time to read the article. As a matter of fact, yes I do use fuel additives and am pretty fond of Fuel Bomb probably because its our own brand! But in all seriousness, we’ve had great success using it ourselves and continually get great reviews, so I’m not the only one that’s happy with it. We have two different blends available, our “standard” F-Bomb (Part Number FB-001) that can be found here:


      And then our Hellfire (Part Number FB-002) shown here:


      In terms of the difference, the standard blend increases cetane (by around 2 points), disperses water, lubricates the fuel system, basically is a good “do everything” type of additives. In contrast, Hellfire is intended to give the maximum increase in cetane that can be had in a fuel additive, resulting in about an eight point increase. Overall, depends on the usage or preference, but I personally use both. I like running Hellfire as it gets the cetane level back closer to 50 points, similar to Low Sulfur Diesel (as opposed to the current ULSD) helping to improve overall power, fuel economy, and reduce smoke output. Then, I frequently run the standard F-Bomb to kind of “clean things out.” WE don’t currently have a winter specific formula, so in instances of extremely low temperatures, I will run an anti-gel.

  24. Hello Josh and fellow Cummins diesel owners. I need help with an ongoing problem over the last year. I have a 2004.5 Ram 3500 Laramie that I purchased in late 2004. My issue is I can be driving along and the truck dies no sputter or warning. So far I have removed tank and cleaned thoroughly, replaced lift pump with air dog, replaced draw straw with air dog kit, replaced fprv, fca, cleaned every ground wire and cleaned adding Dietrich grease, same with all connectors. Always when my truck stalls I have to open the valve on water separator for a second and it will start back up and it might go 2 miles or weeks even months before doing it again. Any help would be appreciated. Also it has been to a diesel shop who only works on Cummins diesels a few times and no permanent fix..

    1. Hey Jim, sounds frustrating! I’m curious, is the fact that you open the drain valve the only thing that will allow it to start? I’m just thinking out loud if maybe its just the time it takes to drain it versus actually purging the system. If it is indeed cracking the valve, then it sounds like it may be releasing air from the system thats trapped. Does it do it when you have a certain amount of fuel in the tank, or less than a certain amount? I’m also wondering if there’s not an issue with the pick up tube in the tank, whether its cracked, not seated at the bulkhead connector on top, or not fastened at the bottom of the fill bucket in the basket. Now, if its more of a coincidence not associated with purging, I would verify the injector harnesses have less than .05 ohms of resistance, same with the injector solenoids, and test injector return rates just to verify there aren’t any issues with that side of the system. When it does stall, hooking up a scan tool or something that communicates to the ECM would verify that the ECM has the proper amount of power and is functioning, as well. Honestly, my first reaction was that it could be that the entire CP3 needs to be replaced, but I am hesitant to say its the CP3 because “usually” when they fail, it will just stop the truck, but you can’t restart it. But if everything around it has been checked and working properly, that seems to be the only other thing it could be.

  25. i just got a 2005 dually with 3.73 and g56 manual and 235000 mjles. i get 15 mpg empty. is this normal or would i benefit from a tuner, cold air, fass, etc? thank you.

    1. Hi Steve, thanks for reaching out and congratulations on the new-to-you truck. The first couple of things I’d question is how you’re using the truck, how much you’re letting it idle to warm up in the morning, and what the ambient air temperatures are like in your area right now. The reason I ask, for instance, we’re located in Spokane Valley, Washington where during the winter as it is now, its pretty standard to let a truck warm up for 5-10 minutes every morning before heading out plus its common practice for many fuel stations to run “winter fuel” that has cold weather inhibitors in it, but that also reduce fuel economy. For these reasons, its somewhat normal in our area for mileage to drop off a bit. Now, regarding your specific truck, unfortunately, the 2004.5 and 2005 models are known for having a lower average fuel economy compared to the 2003 through early 2004, and the 2006 through 2007 5.9L Cummins models. I’ve seen numerous 2004.5’s, for example, only netting 12 MPG’s in stock form, which is obviously pretty dismal. The basic reasoning for the short term drop off is that Ram / Cummins made some changes in this mid-model year to meet newly heightened emissions regulations which included new injectors that fired more times per injection event, new factory tuning calibrations, added a catalytic converter, and more, and until they released the newer ECM’s in 2006 model years, mileage struggled.

      Now, what can you do about it? The items you mentioned are definitely a few things I’d recommend to bump up that mileage, but before I dive into that with specific recommendations, also make sure the truck has been gone through in terms of new fluids, fresh filters, valve adjustment, and so forth. If the truck isn’t currently running synthetic oils, that can make a noticeable difference, as well, plus the other added benefits synthetics will bring.

      In terms of recommendations of what you can install on the truck that have a history of increasing fuel economy, I’d start off with a cold air intake and a programmer for sure, specifically an S&B Cold Air Intake and either a Smarty Jr. or Edge Juice with Attitude. The S&B is available in either a cleanable, oiled filter or a disposable, dry filter. Between the two of those options, its really a matter of whether you would prefer to clean and oil a filter for life versus throwing one away and replacing with new. Here’s a link to the S&B system:


      In regards to adding a programmer or chip, as I’d mentioned, we’ve had great luck with both the Smarty line of programmers, as well as the Edge Juice with Attitude chips. Some of the major differences between the two of these are that the Smarty Jr. is a traditional “programmer” in that you plug it into the OBDII port under the dash, download a file to your ECM, and once its done, the programmer is removed from the vehicle until you want to change any of the settings. In contrast, the Edge is a “chip” in that it plugs into a handful of sensors under the hood of the truck and installs permanently inline with these sensors. Further, it includes an intuitive screen that is mounted in the cab of the truck so you can watch various powertrain parameters and even adjust power levels on the fly as you’re driving down the road, which is pretty handy. We have numerous reports of this alone increasing fuel economy at least 1-2 MPG’s, and the same goes for the S&B. Here are a couple of links to the Smarty and Edge:


      Finally, here are a couple of blogs we’ve written specifically relating to increasing fuel economy.


      Hope all of this helps, and if you have any other questions, please let us know.

  26. Josh, looking at a very low mileage 06 Cummins.(20,000) I read on the web to avoid this year??? Can you elaborate why?

    1. How in the world did you find a 2006 with only 20,000 miles?! In regards to 2006 Cummins, wherever you read that needs to rethink their level of knowledge in these trucks. In contrast, the 2006 to early 2007 5.9’s are typically the most sought after of all Rams. Obviously, this is pre-DPF and EGR, but the 2006-2007’s had jumped into a later style ECM and electronics to allow for better performance tuning, the release of the Mega Cab that a lot of people prefer, and other small details. Buy it!

  27. Ten months ago I had all injectors replaced $5500 with labor right in Coeur d’Alene. Two weeks ago I had white smoke on acceleration (trialing) exhaust smells nasty, poor fuel. Took it in under warranty, they replaced one. It still smokes, they don’t know why. Now they’re saying they can see a bluish tint from exhaust (maybe turbo). I didn’t have these problems before the new injectors. They cannot bench test them for some reason. I cannot drive with the emissions like that. I feel like I’m being stringed along.

    Any ideas?


    1. There could be a lot of different things going on here. First, if the smoke is more blue, then that’s typically oil getting burnt which is not associated with the injectors, of course. I’m also presuming your truck is a 2003-2007 Cummins since that’s what this article is about. How many miles are on the engine and what exact year is it? Why did you originally have the injectors replaced? After they were replaced, was the original issue taken are of? I would start off by removing the intake off of the turbo and inspecting the compressor area of the turbo for oil. If there’s oil there, you blew the compressor seal and its likely the blue smoke is caused by oil working its way to the combustion chamber. If you have a lot of miles, its also possible that your original issue is low compression, yet it was assumed it needed injectors, when it actually didn’t. Pull your dipstick, is your oil level reading high? If so, you’ve probably got oil in your fuel, which could be caused by numerous factors, such as improper installation of the injectors / connector tubes (tube not seated into injector, causing fuel to bypass injector). In regards to the shop not being able to bench test, that part isn’t abnormal, but with the proper scan tool, they should be able to run a contribution and/or return rate test. Here’s an article that may help you, its a pretty elaborate writeup about diagnosing a no start issue on the same truck, but it deals pretty exclusively with testing the fuel system:

  28. The truck is a 2006, 5.9 Ram. I didn’t mean to hijack the article, I was just trying to find out why my truck is worse than before it went in.

    It’s under warranty but they (automotive shop) pretty much said there’s nothing else they can do. They’ve been stringing me along. It will cost them too much money and time.

    Since I owned this Dodge, I’ve dropped $17,000 into last 4 years. New transmission, shift cable, radiator, all injectors, ball joints…all at the same auto shop. But no more, they lost my business.

    I’ve decided to take it to an actual diesel shop. They informed me within one hour they can tell me what’s wrong. That gave me some confidence.


    1. You’re not hijacking the thread at all, that’s why this blog is here in the first place, to help people! Okay, I’m betting the first thing the new shop does is a contribution test where they could pin point if one cylinder is worse than the others, and hopefully its something as simple as needing a new injector harness or a connector tube not seated properly into the injector. Now, if the previous shop didn’t replace the connector tubes when they replaced the injectors, its highly likely you’re not getting a good “seat” between the injector and the tube, causing fuel to leak into the cylinder(s) causing the smoke issue. Its quite important to change tubes with injectors and sounds like this shop may have missed that part. Good luck with the new shop and if you need any recommendations on other shops in your area we may recommend, feel free to get a hold of us.

  29. Answers from your reply.

    1. It has 172,000 miles (2006).
    2. Injectors (all of them) were replaced 10 months ago.
    3. All were replaced but saw some white smoke, informed auto shop. They told me it was condensation.
    4. The recently replaced #4 injector but it didn’t fix the problem.
    5. They don’t know why it’s still smoking from exhaust.
    6. They can’t do anymore.
    7. It’s my only vehicle and is now parked until my appointment on the 19 of September (earliest date).

  30. Update:

    I was able to confirm my Turbo charger is working and has no issues. Its not the source of the smoking issue.

    Went back to Lloyd’s auto and explained the issue. They are refusing to repair their work even though it’s still under warranty. I’m convinced I have a faulty fuel injector that they put in.

    I’m barely getting 12mpg. I used to get 20mpg. I cannot drive it anymore because of the smoke, nasty smell, and loss of fuel (200 miles).

    I guess I’m going to pursue legal action against Lloyd’s Automotive in CDA.

  31. 2005 5.9/auto/dually with 156,000 miles on it, bone stock. On a summer trip, in relatively flat country, it developed what sounded ‘like an intermittent shorting sparkplug’ in a gas engine. We carry a ‘load’ of a 5000 pound slide-in camper. The ‘miss’ is when the trans goes into OD (trans rebuilt 30k ago), and is barely detectable to most and occurs mostly when on cruise control in the 55-65 mph range. Accelerating hard or running out of OD gaining speed detects no ‘miss’ which is described as a low frequency, boop-boop—-boop—-boop-boop sound/feel. We tried some injector cleaners, etc. thinking it was a sticking injector. When that didn’t help we returned the 400 miles to home with the issue ever present.

    Cursory things such as the FCA, filters, fuel, cleaners, etc. were repeatedly changed to no effect. We contracted our independent diesel shop to change the entire fuel system with Bosch reman injectors, a new Bosch CP3, and an AirDog which I wanted anyway out of PMaint. But, unfortunately, all that effort didn’t fix the low frequency, steady-light-throttle ‘miss’. You sometimes can actually hear the boop-boop at idle when you are standing far behind the truck in a driveway.

    Because of the slow work of the shop, I chose not to even mention that they hadn’t fixed the issue which they too thought was an injector problem. It was so difficult to detect, unless The truck does run strong and their install was something I wanted anyway for the future of my possession of it.

    With such a complete changeout of the fuel system with quality parts, I’m now thinking electronic. A couple of questions I am wondering about. Would adjusting the valves (they were done at 100k) cause such a low frequency intermittent miss? Would a clogging Cat Converter be a possibility? Could the ECM be firing misfiring the pre-charge or post charge the injectors do? How about Ohming the injector solenoids? Injector harnesses? Compression test? If it’s an ECM issue, would reflashing the ECM at the dealer be a possibility? (Never done for bags and reflashing bulletins). Would a Smarty, Jr. perhaps correct an ECM issue? How about turbo or waste gate?

    I would like to hear your approach to what might be a plan of exploration.

    1. Thanks so much for the question and thorough explanation. The first thing that comes to mind would be the pressure relief valve (PRV) on the rail is sporadically dumping fuel causing both this noise and the surge. Normally, once the PRV gets to a point, it will be relieving excess fuel most noticeable at higher RPM’s, causing a lack of power, however, I/we have seen instances in which it will be unable to sustain a specific pressure and acting in a very similar manner as what you’re describing. I (Josh) personally drive an early 2004 Cummins that has a very similar (nearly exact) fuel system and I experienced a similar issue. In order to diagnose it easily, I would recommend installing a pressure relief block off. In doing so, it will completely eliminate the PRV altogether, which does remove a common failure point, but it also removes a safety in the system in the event you were to ever have a surge in rail pressure, it would now all go to the injectors. For testing purposes, I have never seen any issues, and I personally run a block off all of the time.

      The second thing that comes to mind would be to ohm test all of the injector wires. In case you hadn’t seen it, we actually have a pretty thorough explanation on how to diagnose a no start situation, but the same procedures are done when diagnosing the fuel side of what you’re experiencing. That can be found here:


      Other things came to mind such as a pin hole in an intercooler boot, or even your intercooler end tank as your 2005 is the ONLY year that Ram opted to have plastic end tanks instead of cast. But, you shouldn’t be able to hear anything when sitting at idle as the truck isn’t under boost, but it would make a ticking noise as boost increases. That said, I’d still run a boost leak down test to confirm you don’t have a hole somewhere causing the noise.

      Have you or anyone else checked out the turbo itself? While again, it really isn’t going to be making any boost at idle, the wheel will usually be slightly turning and want to make sure its not striking the inside of the housing. This can be checked simply by removing the tube on the front of the turbo and wiggling the compressor wheel by hand with the vehicle turned off.

      Lastly, with a scan tool plugged in, you can verify that the torque converter is locked and staying locked up when you’re cruising down the road. While it wouldn’t create the noise at idle, when you’re cruising down the highway in that 55-65 mpg range you’re mentioning, if the converter is coming in and out of lockup, it would definitely create a shuttering feel and potentially a noise.

      Hope this helps, please let us know how your diagnosis goes.

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