MULTI-PORT FUEL INJECTION DESCRIPTIONS AND SYSTEM OPERATION
SERVICE MANUAL NUMBER 23
90-861326--1 MARCH 1999 Page 5B-39
7.4L MPI Multi-Port Injection Components
FUEL PUMP ELECTRICAL CIRCUIT
When the ignition switch is turned to the RUN position, the ECM will turn ON the fuel pump
relay for two (2) seconds.
When the ignition switch is turned to the crank position, the ECM turns the fuel pump relay
ON causing the fuel pump to start.
If the ECM does not receive ignition reference pulses (engine cranking or running), it shuts
OFF the fuel pump relay, causing the fuel pump to stop.
FUEL RAIL / INTAKE MANIFOLD ASSEMBLY
The fuel rail performs several functions. It positions the injectors in the intake manifold, dis-
tributes fuel evenly to the injectors.
75615
a
b
c
d
a-Fuel Rail
b-Fuel Injector
c-Intake Manifold
d-Plenum
FUEL INJECTORS
The EFI injector assembly is a solenoid-operated device, controlled by the ECM, that meters
pressurized fuel to a single engine cylinder. The ECM grounds the injector solenoid, which
opens a pintle valve, allowing fuel to flow past the pintle valve. The injector tip has holes that
control the fuel flow, generating a conical spray pattern of finely atomized fuel at the injector
tip. Fuel is directed at the intake valve, causing it to become further atomized and vaporized
before entering the combustion chamber.
An injector that is stuck partly open will cause loss of pressure after engine shutdown. This
can result in long cranking times. Dieseling or delayed shutoff can also occur, because some
fuel might be delivered to the engine after the ignition is turned OFF.
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