Mercury MerCruiser MCM 454 Mag MPI Service Manual page 665

GENERAL SYSTEM DIAGNOSTICS
Chart A-4 (1 of 5): Fuel System Diagnosis
CIRCUIT DESCRIPTION:
When the ignition is turned "ON," the Engine Control Module (ECM) will turn the fuel pump
"ON" for 2 seconds. During engine cranking, the ECM will turn "ON" the fuel pump. It will
remain "ON" as long as the engine is cranking or running, and the ECM is receiving ignition
reference pulses. If there are no reference pulses, the ECM will shut "OFF" the fuel pump.
The pump will deliver fuel to the fuel rail and injectors, then to the pressure regulator, where
the system pressure is controlled to about 34-38 psi (234-262 kPa). Excess fuel is then
returned to the water separating fuel filter.
DIAGNOSTIC AIDS:
An intermittent may be caused by a poor connection, rubbed through wire insulation or a
wire broken inside the insulation. Check for the following items:
Poor connection or damaged harness. Inspect the ECM harness and connectors for
improper mating, broken locks, improperly formed or damaged terminals, poor terminal
to wire connection and damaged harness.
Contaminated or dirty fuel may cause the fuel pump to seize, which will cause the fuel
pump relay fuse to fail.
The ability to maintain a constant fuel pressure is very critical in the driveability of fuel
injection. If the fuel pressure drops below the specification of that application, multiple
driveability problems may occur. The vessel may have to be operated under a load, or
certain conditions, as the lack of fuel pressure may be intermittent.
Index
Page 5E-72
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SERVICE MANUAL NUMBER 23
FUEL SHUT-OFF TOOL
75752
90-861326--1 MARCH 1999