Cummins ISX Fuel Pressure Relief Valve
The Cummins ISX Fuel Pressure Relief Valve helps to regulate fuel pressure by bleeding off excess fuel pressure from the fuel rail. This part has been updated multiple times and is a common source of everything from low power complaints to low fuel rail psi codes. It is a simple part that can cause major head aches. This article is specific to the Cummins ISX 15 and X15 engines. For more Cummins specific how to guides, visit our Cummins page.
Cummins ISX Fuel Pressure Relief Valve Location
On the ISX 15, the fuel pressure relief valve is on the end of the fuel rail toward the front of the engine. It is screwed directly into the fuel rail on one end and has a banjo type fuel line fitting on the other which is sealed by 2 sealing washers.
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Relief Valve Replacement Procedure:
- Park truck in a level spot and make sure keys are removed or in the OFF position
- Locate relief valve located on the front of the fuel rail
- Using a 7/8” wrench, loosen the banjo bolt that connects the fuel line to the relief valve – some fuel may drain from fitting but if excessive fuel drains out that could be an indicator of a faulty relief valve
- Remove bolt and sealing washers
- Using a 1 1/16” wrench, loosen the relief valve from the fuel rail
- Remove valve from fuel rail
- There is a crush washer in the fuel rail that should technically always be replaced when the relief valve is removed – I personally have had no issues with inspecting the washer and reusing it if it is found to be in visually good condition. It is tight in the fuel rail and would need to be pried out to be replaced
- Install new fuel pressure relief valve
- Reinstall fuel rail using the banjo bolt and sealing washers (it is recommended to use new sealing washers if available)
- Start engine and check for leaks
