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Cummins ISB CM550 (1990-94) Fault Code: 368 PID: SID 254 SPN: 1078 FMI: 8 Fuel Pump Can Not Reach Commanded Timing

Circuit Description
The fuel pump uses an internal check to determine if the fuel injection pump can reach the
commanded timing.

Component Location
The fuel pump circuit is internal to the fuel pump.

Shop Talk
The fuel pump uses pressure generated by an internal vane-type transfer pump and its timing
solenoid to vary the fuel pump’s timing according to the specified ECM commands. Possible causescan be classified into four groups:
1) Static timing – offset key, gear train issues
2) Low-pressure fuel supply issues – restriction issues, low supply pressure
3) Fuel pump return plumbing issues – high return restriction, overflow valve issues
4) Noise in the engine position pulse signal.