90-823225--1 10965E-68 - ELECTRONIC FUEL INJECTION (MULTI-PORT AND THROTTLE BODY)
Throttle Body Injection Fuel System Diagnosis
Chart A-7 (1 of 6)
FUEL LINE TO
ELECTRIC FUEL PUMP
SHUT-OFF TOOL
WATER SEPARATING
FUEL FILTER
IMPORTANT: Check for contaminated fuel tank,
stuck anti-siphon valve or fuel system vacuum
leak anywhere before the electrical fuel pump
and after the fuel pressure regulator.
CIRCUIT DESCRIPTION:
During engine cranking, the Engine Control Module
(ECM) will turn ON the electric fuel pump. It will re-
main ON as long as the engine 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 injectors and pres-
sure regulator, where the system pressure is con-
trolled to about 30 PSI (207 kPa) nominal. Excess
fuel is then returned to the water separating fuel filter.
TEST DESCRIPTION:
Number(s) below refer to circled number(s) on the
diagnostic chart.
NOTE: If pump does not run, check fuel pump relay
and fuse.
1. Install the fuel pressure adapter in-line at the
throttle body.
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, pump pressure should be 28-32 PSI
(234-207 kPa). This pressure is controlled by
spring pressure within the regulator assembly.
3. Pressure that leaks down is caused by one of the
following:
• Fuel pressure regulator valve leaking.
• Injector(s) sticking open.
• Check valve in fuel pump leaking.
4. An injector that is stuck open will leak or drip fuel
into the plenum of intake manifold, which may
saturate or foul spark plug(s). In order to deter-
mine which injector is leaking, remove the flame
arrestor and observe both fuel injectors with “key
on” and “engine off”.
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