Fuel System Diagnosis
Diagnostic Instructions
Circuit/System Description
The engine control module (ECM) enables the fuel pump relay when
the ignition switch is turned ON. The ECM will disable the fuel
pump relay within 2 s unless the ECM detects crankshaft reference
pulses. The ECM continues to enable the fuel pump relay as long as
crankshaft reference pulses are detected. The ECM disables the fuel
pump relay within 2 s if crankshaft reference pulses cease to be
detected and the ignition remains ON.
The fuel tank stores the fuel supply. An electric fuel pump
attaches to the fuel pump module inside the fuel tank. Fuel flows
to the fuel filter/heater element housing , which combines a water
separator, fuel heater element, and a filter element. The fuel is
then delivered to the high-pressure pump. The mechanical fuel
injection pump is located at the front of the engine. The
mechanical fuel injection pump is engine driven by the timing belt.
From the high-pressure pump, the pressurized fuel flows to the fuel
rail. The fuel rail is equipped with a fuel rail pressure sensor
and a fuel pressure regulator.
The fuel return system returns not used fuel to the fuel tank.
Fuel is used to cool and lubricate the fuel injectors and fuel
injection pump. If the high side fuel pressure becomes excessive,
the fuel pressure regulator releases the fuel into the fuel return
system . The return fuel travels through the fuel lines and then to
the fuel tank.
Diagnostic Aids
A Cranks But Will Not Run or Hard Start symptom may exist if air
is being drawn into the fuel injection system due to the following
conditions:
• |
Deformed or cut O-rings at the
fuel supply line connections |
• |
Improperly seated fuel supply
line fittings |
• |
Porous or weathered rubber
fuel supply lines |
• |
Fuel filter vent screw not
tighten or cross threaded |
• |
Fuel filter not tighten
properly |
Reference Information
Schematic Reference
Engine Controls Schematics
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
Note:
• |
Inspect the fuel
system for damage or external leaks before proceeding. |
• |
Verify that
adequate fuel is in the fuel tank before proceeding. |
1. |
Ignition ON, command the Fuel
Pump Relay ON and OFF with a scan tool. You should hear the fuel
pump turn ON and OFF. |
2. |
Observe the scan tool Fuel
Rail Pressure Sensor parameter. During engine cranking, the
pressure should be at least 415 kPa (60 PSI). With the engine
running at idle the pressure should be close to the Desired Fuel
Rail Pressure parameter. As the engine speed is increased, the
Desired Fuel Rail Pressure parameter and the Fuel Rail Pressure
Sensor parameter should closely match each other. |
Circuit/System Testing
|
Note: It may be
necessary to remove engine components for the visual
inspections.
|
1. |
Verify the following
conditions do not exist: |
|
• |
Hoses and lines that are
flattening when the engine is running, or have kinks that may
restrict the flow of fuel |
|
• |
Fuel leaks between the fuel
tank and the fuel injection pump |
|
Note: A fuel return line
that is leaking , is a good indication there is a restriction in
the return system.
|
|
|
|
|
• |
Fuel leaks in the fuel return
lines |
⇒ |
Repair any leaks, restrictions, or replace any
components found to be damaged or leaking. |
2. |
Install the fuel pressure
gauge. |
|
Note: The fuel pump
relay may need to be commanded ON a few times in order to obtain
the highest possible fuel pressure.
|
3. |
Ignition ON, command the fuel
pump relay ON with a scan tool. Verify the fuel pressure is between
415-535 kPa (60-78 PSI) and remains steady for 5 min. |
⇒ |
If less than the specified range, remove the fuel
tank and test, inspect, and repair the items listed below. If all
items test normal, replace the fuel pump. |
|
• |
Restricted fuel feed
pipe |
|
• |
Restricted or plugged
strainer |
|
• |
Stuck or binding fuel level
float |
|
• |
Inspect the harness connectors
and the ground circuits of the fuel pump for poor
connections. |
4. |
If the fuel system components
test normal, test or replace the fuel filter. |
Repair Instructions
Perform the
Diagnostic Repair Verification after completing the diagnostic
procedure.
|