90-823225--1 10965E-62 - ELECTRONIC FUEL INJECTION (MULTI-PORT AND THROTTLE BODY)
Multi-Port Injection Fuel System Diagnosis
Chart A-7 (1 of 6)
SCHRADER
VALVE
CONNECT
FUEL
PRESSURE
GUAGE
HERE
FUEL INLET
PORT FUEL RAIL
STARBOARD FUEL RAIL
LATER STYLE (MCM & MIE) FUEL LINE ROUTING
(BLACK SCORPION FUEL INLET IS
LOCATED ON THE REAR OF STARBOARD FUEL RAIL)
SCHRADER
VALVE
CONNECT
FUEL
PRESSURE
GUAGE
HERE
FUEL INLET
STARBOARD FUEL RAIL
PORT FUEL RAIL
FUEL RETURN
EARLIER STYLE (MCM & MIE) FUEL LINE ROUTING
CIRCUIT DESCRIPTION:
During engine cranking, the Engine Control Module
(ECM) will turn ON the electric fuel pump in the vapor
separator tank. It will remain ON as long as the en-
gine is cranking or running, and the ECM is receiving
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 36 PSI (248 kPa)
nominal. Excess fuel is then returned to the vapor
separator tank.
TEST DESCRIPTION:
Number(s) below refer to circled number(s) on the
diagnostic chart.
1. If pump does not run check fuel pump relay and
fuse.
2. Wrap a shop towel around the fuel pressure con-
nector to absorb any small amount of fuel leak-
age that may occur when installing the gauge.
Ignition ON. This pressure is controlled by spring
pressure within the regulator assembly.
3. When the engine is idling, high vacuum is applied
to the fuel regulator diaphragm. This will offset
the spring and result in a lower fuel pressure. This
idle vacuum will vary somewhat depending on
barometric pressure; however, the fuel pressure
at idle should be less, indicating fuel pressure
regulator control.
4. Pressure that leaks down is caused by one of the
following:
• Fuel pressure regulator valve leaking.
• Injector(s) sticking open.
• Check vent line from VST to see if diaphragm
is leaking.
5. If an injector is stuck open, it will send fuel to its
respective cylinder, which may saturate or foul
spark plug(s). In order to determine which injec-
tor is leaking, the spark plugs must be removed
and inspected for fouling or saturation. Once the
saturated spark plug(s) is found, replace the cor-
responding injector(s) and install new spark
plug(s).
FUEL PRESSURE
Description
Specification
Multi-Port Fuel Injection
With Vapor Separator
Tank
43 PSI (206 kPa)
Multi-Port Injection With
Cool Fuel System
30 PSI (296 kPa)
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