We get a lot of calls on a daily basis with customers trying to diagnose some type of issue with their truck, and once diagnosed, with recommendations for products or procedures to remedy the issue.  We must have developed quite a name for ourselves over the years, as frequently we even get calls from shops that are scratching their heads, hoping we have the golden ticket, and fortunately, we usually do!  One of the most common calls we get are from customers with a 2003-2007 Cummins that have developed either a hard start or no start condition.  In order to help out, we had our Assistant Sales Manager, Tyler Lucas, put together this step by step tutorial that you will hopefully find insightful.   Tyler has been elbow deep in diesel engines for years, especially Cummins, so he is a wealth of information when trying to cure a plagued engine.
The very first thing that needs to be checked is battery voltage.  When I say battery voltage, I am not talking about just getting a voltmeter and putting it on the positive and negative posts, as you will only get what’s called a surface charge, which won’t tell you what’s actually going on when the battery is under load (i.e. cranking).  It is very common to have a battery read around twelve volts on a surface charge, but then drop well below nine (the minimum voltage to allow for cranking on 2003 to current Cummins) when under load.  Overall, make sure that when you test the battery, you are doing so under load by cranking the engine and watching the voltmeter.

Let’s now say your batteries are good.  You then ask yourself, “Tyler, what now?”  Don’t worry sad no start truck, we’ve got your back!  Let’s now dive into the fuel system.  First off, let’s get this out of the way, Ram trucks NEVER had the best luck with lift pumps.  A lack of lift pump flow will not only cause a no start issue, but depending on how it failed, can cause other issues that we will discuss further into this post.  The factory lift pumps on the 2003-2007 Cummins produce a dismal 10-11.5 PSI at idle.  But unfortunately, due to these pumps’ inability to actually produce volume, the pressure drops off considerably as load increases.  And remember, while pressure is definitely an important factor as this is the rate at which fuel is dispensed, volume is equally, if not more important, as it’s the amount of fuel.  This drop in pressure is even greater when fueling modifications and upgrades are added, such as programmers, upgraded larger displacement injectors, and higher volume injection pumps, because guess what, they are all demanding additional fueling for increased performance.  When you start going below 5 PSI, you are not supplying the injection pump with enough fuel to properly drive the injectors, and at the very least, you will experience a loss of power and fuel economy.  Some customers will notice the truck “falling on its face” or flat lining with power as the pump simply cannot supply any more fuel.  After time, the pump will just stop working due to being over stressed and constantly running at maximum output.  And this is exactly what we will be testing for next, the health of the lift pump.  The best way to check your fuel pressure is to install an inline pressure gauge before the injection pump.  But we understand that in many instances when your truck won’t start, you simply don’t have the time or resources to collect the parts and tools to accomplish this.  So we have an alternative method for you by checking the general volume output of the pump.  In order to do this, remove the fuel supply line before it connects to the injection pump and place the open end into a bucket under the truck.  Next, hop in your truck, and “bump” the key.  When I say bump the key, just turn the key to crank the engine for a second in order to engage the pump.  At this point, you should hear the pump run the duration of its  cycle.  For reference, the 2003-2004.5 trucks came equipped with a block mounted lift pump and the 2005-2007 trucks came from the factory with an in-tank lift pump, yet many of the 2003-2004.5 trucks were later retrofitted with this same in-tank design.  This will give you a gauge on where to listen for the “hum” of the electric motor on the pump.  Once you’ve bumped the key, presuming the pump is operating normally, you should see fuel dumping into the bucket.  However, if no fuel comes out, then it’s safe to assume that this is the culprit of your no start issue.  In order to correct, you’ll need to replace the lift pump, and no better time to upgrade than now.  Our preferred brands of aftermarket lift pumps are FASS and AirDog, simply because they have options for stock to fully modified engines, offer filtration that is far superior to stock for increased protection, and come standard with a lifetime warranty.  Out of those manufacturers, our most popular models are without a doubt the FASS Titanium and AirDog II-4G.  For most trucks, even slightly modified, a volume of 95 or 100GPH is ample to properly supply the injection pump for a lifetime of trouble free service.  And just remember, bigger isn’t always better in terms of lift pump choice.

But Tyler, I checked that and everyone knows that Dodge lift pumps are sub-par at best.  Stay with me here, we are graduating to the high pressure side of the fuel system now.  One of the most common problems I see on common rail Cummins, is the pressure relief valve, or PRV for short.  For those unsure of exactly what I am talking about, this is the large fitting on top of the fuel rail that has a fuel line attached to the top of it via a banjo bolt that then returns fuel back to the factory fuel filter.  The pressure relief valve is designed to do just as the name implies, relieve pressure.  Specifically, it begins to open at 26,000-27,000 PSI and return any excess fuel to be recycled back into the system.  Commonly, these valves will get stuck in the open position and stay that way when the truck is turned off.  If the valve is stuck in the open position, the truck is unable to build the necessary fuel rail pressure (5,000-7,000 PSI) for startup.  Remember, this is a common rail system and that pressure is absolutely necessary for the fuel to be atomized properly to create combustion.  To visualize this, imagine trying to blow up a balloon with a gaping hole in the side of it, not happening, right?  In most cases, we sell either a new replacement pressure relief valve to return the system to stock, or a PRV Block Off to eliminate the relief valve all together.  Some would argue that installing a block off is unwise when combined with a factory fuel system because it cannot protect itself against pressure spikes. Now, I have been around these engines quite a bit, and have installed countless block offs in completely stock trucks without a single issue.  This fuel system is designed to handle exceptionally high pressure, so a small spike in pressure for .00001 of a second should not cause any damage. The benefit of installing a block off as opposed to a new PRV?  Well, that’s simple; number one you’ll never have to worry about a blown PRV again, and secondly, a block off is substantially less money.  With that said, I Pressure Limiting Valvedon’t recommend running a stock fuel system with a rail pressure box, such as the TS-MP8 on its max setting, combined with a block off, as it will over stress the fuel system.  Which one is right for you?  That’s up to you and your truck, but as always, if you need guidance, feel free to contact us and we will help steer you in the right direction.

Before we go to another portion of the fuel system, another quick check is the transfer or connector tubes. This is the part that transfers fuel from the high pressure common rail to the injectors. The fuel line from the rail connects to the inlet and is seated against the injector via a jam nut. There was actually a TSB (Technical Service Bulletin) from Dodge years ago regarding the tubes losing torque, causing them to leak between the injector and the tube. This can easily be checked by removing each individual fuel line and checking the jam nut to ensure it has the proper torque. I torque tubes to around 55 ft. lbs., factory spec is 35 ft. lbs.

Now you may say, “guess what Tyler, I’ve already checked that, what’s next on the docket?”  Well fellow Cummins connoisseur, I have your back yet again.  This next test gets a little more involved.  Each of the six injectors in your engine will return fuel.  The maximum amount of leakage on a warm engine is 160 mL per minute at about 1200 RPM’s.  During cranking, you want to see 90mL, or about the amount of fuel that would fit in a double shot glass, essentially not a lot of fuel.  In order to perform this test, you will need that trusty bucket yet again to capture the return fuel, as well as a small section of hose that will be used to extend the return line somewhere where you can watch and hold the bucket.  If you look in the driver’s side front fender well, there are two hard plastic fuel lines with a clip attaching them about halfway up the engine. One is a return from the CP3 injection pump coming out of the fuel filter canister, and the other is for the injectors coming from the back of the head. Make sure you are only dealing with the line coming from the back of the head. You will take that line and detach it by releasing the clip.  Now that the return line is free, attach your hose to extend into your trusty bucket.  Finally, have a helper hop in the truck and start cranking.  Unfortunately, this particular test requires you to crank the engine for an entire minute, which will seem like an eternity to you, your starter, and your batteries.  Being the spec is only 90mL, if you have gone past that in the first 15 seconds, just stop, as we know there is a problem at that point.  Usually a good working set of injectors that are returning the proper amount of fuel will just lightly trickle out of the return line.  Any result over 90mL means the injectors are returning excessive fuel, and they either need to be repaired or replaced.  This is also a great test if you have lost fuel economy, but the truck seems to be running properly.  A slight drop in injection pressure caused by excessive return will cause improper atomization, therefore decreasing efficiency. That’s another topic I’m sure I could elaborate on for a few pages about, but that’s for another day!

If you have checked everything and we still have a no start condition, I would look at the CP3 injection pump. The only way to really test the output of the CP3 is to send it to a fuel shop and get it on a test stand. There is one test you can do at home, but it is definitely a backyard mechanic test, and not a true determinant for the health of the pump. We will be looking at the Fuel Control Actuator, also known as the FCA, M PROM, and I have even had people call it a pressure regulator.  This is the two wire actuator coming off the back of the CP3, and is the only electronic connection on the pump. This sensor basically tells the CP3 what pressure it needs to be at.  In some instances, this actuator will either get stuck in a certain position or stop operating altogether. When this sensor is unplugged, the pump loses its ability to restrict flow, thus will run at maximum pressure, which is exactly how we will run this test!  We are going to unplug the FCA and attempt to start the truck.  Keep in mind you Cummins techs out there that say this is not a valid test, as this test is not for you.  This test is for the hard working Average Joe that doesn’t want to take his truck to you and pay your $120 per hour labor rate.  Alright, now back to the test, if the sensor is unplugged and the truck starts, we can assume the sensor is not functioning FCAproperly, which again, is a very commonly failed component.  Now very important, if the truck starts, make sure you quickly turn it off, as with the FCA unplugged, there is no metering of the CP3, which means it will run at maximum capacity, causing elevated RPM’s and a rough idle.

All of the above tests are intended for the do-it-yourselfer, and will typically lead to the underlying cause of the issue in most instances we have encountered.  However, if after performing these tests the diagnosis is still uncertain, the problem is probably more in-depth.  As always, if you have any questions about the above information or any of the products mentioned, do not hesitate to give us a call or send an e-mail to [email protected] and we would be happy to assist.

Tyler Lucas
Assistant Sales Manager
[email protected]
(888) 99-DIESEL Ext. 103

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