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Cummins ISB CM550 (1990-94) Fault Code: 369 PID: 1690 SPN: 1078 FMI: 2 Fuel Pump To Engine Synchronization Pulse Not Recognized

Circuit Description
The engine control module (ECM) receives a signal from the engine speed/position sensor. This signal is then sent to the fuel pump to indicate where top dead center is for each cylinder.

Component Location
The engine speed/position sensor is located on the fuel-pump side of the block, behind the starter.

Shop Talk
The fuel pump controller monitors/processes 10- to 12-VDC square wave signals at pin 8 (engine harness pump end). The leading edge of this wave is the top dead center reference for the pump. The reference signal must occur within a defined window. If an engine pulse is not recognized within a window, the pump controller sets an error (bit 12). If a final error (bit 13) is set, Fault Code 369 is triggered after 10 seconds while the engine is operating. If Fault Code 368 occurs along with Fault Code 369, verify the engine static timing. Most occurrences of this fault are due to improper wiring by original equipment manufacturer (OEMs) or to grounding issues, loose/shorted wires, or electrical noise.