Failure mode - Cummins 6.7L ISB Diesel (Ram HD)

Lift pump / fuel delivery weakness

Reliability tier: verified - verify before ordering, see /disclosure/

Symptoms

P0087 / low-rail-pressure DTCs, worse under load or with tuning
long cranks, hesitation, power loss when the tank is low
FCA (fuel control actuator) ticking / rough idle when failing
water-in-fuel warnings if filtration is neglected

Compare with the other causes of the same sign on this engine: hard start, long crank or no-start (2 causes) · loss of power, limp mode or derate (6 causes) · ticking, knocking, rattle or whine (7 causes) · misfire, rough idle, hesitation or surging (5 causes)

Root cause

The factory in-tank lift pump is adequate for stock but marginal for sustained towing and tuning; as it weakens (or the suction-side orifices restrict) the CP3 starves - confirmed by low supply pressure. The FCA on the CP3 is a wear item that causes ticking and rail-pressure instability. Water and dirty fuel kill both injectors and pumps.

Diagnosis

measure supply/return fuel pressure under load (the decisive test) - spec per service data
scan rail-pressure actual vs desired under a load test; P0087 points delivery-side first
isolate FCA vs lift pump: FCA symptoms (ticking/rough idle) vs delivery starvation under load
check filter restriction and drain water separator

Fixes

replace the worn lift pump with a stock-type in-tank unit (stock trucks) ()

lift-pump - more than one option: 6.7 Cummins In-Tank Lift Pump (stock type), 6.7 Cummins In-Tank Lift Pump (current service PN 5145571AB)

higher-flow lift pump / frame-mounted filtration+pump system for towing and tuned trucks ()

6.7 Cummins Lift Pump System (high-flow upgrade)

replace the FCA when ticking/rail instability points at it ()

6.7 Cummins Fuel Control Actuator (FCA, on CP3)

Prevalence

common

Parts for this repair run about $80-$860: see them next to the other repairs on this engine in repair costs.