Impco HHI, Service Manual

Page: 64 / 485

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GASOLINE SYSTEM DIAGNOSIS
Gasoline Injection Systems
FUEL SYSTEM DESCRIPTION
The Engine Control Module (ECM) receives in-
formation from various engine sensors in order
to control the operation of the fuel injectors. The
electric fuel pump prevents fuel
flow unless the
engine is cranking or running. During Key ON,
the electric fuel pump receives a short prime
cycle from the ECM which allows gasoline to
flow from the tank through fuel filter and fuel
lines to the pressure regulator before it reaches
the fuel injector. With the Ignition ON engine
OFF and fuel pump running, the pressure
should be
TBD-TBD kPa (TBD-TBD psi). At
idle, manifold pressure is much lower than at-
mospheric pressure, which creates a high
vacuum. This vacuum will offset the pressure
regulator diaphragm, resulting in a lower fuel
pressure. Fuel pressure at idle will vary some-
what depending on barometric pressure but
should be approximately 69 kPa (10 psi) less
than the ignition ON engine OFF pressure. Un-
used fuel is returned to the fuel tank by a sepa-
rate return fuel line. The fuel pump pressure
test port is located on the fuel rail.
DIAGNOSTIC AIDS
This procedure is intended to diagnose a ve-
hicle operating on Gasoline. If the vehicle will
not continue to run on Gasoline, refer to
Hard
Start section for preliminary checks. Before
starting this procedure, verify that the vehicle
has a sufficient quantity of fuel.
TOOLS REQUIRED:

J 34730-1 or equivalent

J 37287 or equivalent
DIAGNOSTIC SCAN TOOL

Diagnostic Scan Tool Software (DST).