Fuel System Diagnosis
Diagnostic Instructions
Circuit/System Description
The fuel tank stores the fuel supply. 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 limiter.
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
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. |
Observe the scan tool Fuel Rail Pressure Sensor parameter.
During engine cranking, the pressure should be at least 20 MPa (2
900 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 |
| 2. |
Repair any leaks,
restrictions, or replace any components found to be damaged or
leaking. |
| 3. |
Engine running, observe the
scan tool Fuel Rail Pressure Sensor parameter. The reading should
be greater than 20 MPa (2 900 PSI) |
| ⇒ |
If less than the specified range, remove the fuel
tank and test, inspect, and repair the items listed below. |
| |
• |
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.
|
