3B - 4 Fuel Metering System 6.0L
MEFI 4 - PCM
Fuel Pump Electrical Circuit
When the ignition switch is turned “ON,” the ECM turns
the fuel pump relay “ON” for two seconds causing the fuel
pump(s) to pressurize the MEFI fuel system.
When the ignition switch is turned to the crank position,
the ECM turns the fuel pump relay “ON” causing the fuel
pump to run.
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.
An inoperative fuel pump relay will result in an “Engine
Cranks But Will Not Run” condition.
Fuel Rail Assembly
The fuel rail (Figure 3-3) is mounted to the engine intake
manifold, and performs several functions. It positions the
injectors (3) in the intake manifold, distributes fuel evenly
to the injectors, and integrates the fuel pressure regulator
(2) into the fuel metering system.
Figure 3-3 - Fuel Rail Assembly
Figure 3-4 - Fuel Injector Assembly (Typical)
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Fuel Injectors
The Multec 2 fuel injector assembly is a solenoid
operated device, controlled by the ECM, that meters
pressurized fuel to a single engine cylinder. The ECM
energizes the high-impedance (12.2 ohms) injector
solenoid (1) to open a normally closed ball valve (2).
This allows fuel to fl ow into the top of the injector,
past the ball valve and through a director plate (3) at
the injector outlet. The director plate has four machined
holes that control the fuel fl ow, generating a spray of
fi nely atomized fuel at the injector tip. Fuel from the
injector tip is directed at the intake valve, causing it to
become further atomized and vaporized before entering
the combustion chamber. An injector stuck partly open
can cause a loss of pressure after engine shutdown.
Consequently, long engine cranking times would be
noticed on some engines.
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