Bosch Pressure Relief Valves

One of the most commonly failed components of a common rail fuel system is that of the pressure relief valve. Why? In short, this relatively simple valve is located on the fuel rail before the injectors and after the injection pump and its intended purpose is to regulate fuel rail pressure before the fuel hits the injectors. It acts as a wastegate to bypass excessive pressure and return that diesel to the fuel system. Unfortunately, this valve (sometimes called a PRV for short) has an internal spring that is known to fatigue, allowing fuel to bypass before necessary. Imagine trying to fill up a balloon with a hole in it, basically the same principle. While some will take the route of installing a pressure relief block, this will allow any unaccounted for spikes in the fuel system to have no choice but to be run through the injectors, potentially causing harm. The most common reasons for spikes are from chips or programmers that ramp up rail pressure substantially beyond factory limitations and/or failing injection pumps, or parts of the injection pump, most namely the Fuel Control Actuator (FCA) and pump gear.

In most cases, a failed pressure relief valve will lead to hard start or no start situations because the truck can't build enough rail pressure to fire. The simplest method to confirm if your truck is in need of a new relief valve is to remove the return line located on the top of the PRV and have someone crank the truck while you inspect the top of the relief valve. If there is fuel present, and especially if its trickling out at start up pressure, you need a new valve.

As always, if you've got any questions about your pressure relief valve or anything else, please do not hesitate to give us a call at 888-993-4373 or send an e-mail to cs@dieselpowerproducts.com and we would be happy to assist.