Code P0087 (Fuel Rail/System Pressure - Too Low) on the 6.7L Cummins means the common-rail fuel system cannot build or hold the pressure the ECM commands. This guide covers what triggers P0087, how to diagnose it, and the parts that fix it.
What P0087 means
The high-pressure fuel system feeds the rail from the CP3 injection pump, supplied by the lift pump. P0087 sets when actual rail pressure falls short of the commanded target - usually a supply, pump, or leak problem rather than the injectors.
Common causes
- Weak or failing lift pump / low supply pressure
- Clogged fuel filter or water in the fuel
- Worn CP3 high-pressure pump
- A leaking injector bleeding off rail pressure
- Failing fuel pressure relief valve or FCA
Symptoms you'll notice
- Power loss and a dead-pedal under load
- Hard starting or a no-start
- Stalling
- Reduced fuel economy
How to diagnose it
Start with supply pressure at the CP3 inlet on a gauge - low supply is the most common cause and the cheapest fix. Then check rail pressure data (commanded vs actual) under load, inspect the filter for debris/water, and rule out a leaking injector by return-flow testing.
The fix
Fix the supply side first: fresh fuel filter, confirm strong lift-pump supply pressure, and address water. If supply is good and the CP3 cannot hold pressure, the high-pressure pump is replaced; a leaking injector is replaced. Add a fuel-pressure gauge to catch supply drop early.
Frequently asked questions
Is P0087 serious?
It causes power loss and can leave you stranded. Start with fuel supply pressure and filtration before condemning the pump.
Can a fuel filter cause P0087?
Yes - a clogged filter or a weak lift pump restricting supply is one of the most common causes.
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