Checking the Fuel Delivery System

CHECKING THE FUEL DELIVERY SYSTEM

Checking The Fuel Delivery System:

POSSIBLE CAUSES
- Restricted fuel supply line
- Fuel pump inlet strainer plugged
- (N1) Fuel pump relay output circuit open
- Fuel pump relay
- Fuel pump

Diagnostic Test

1. FUEL PUMP OPERATION

Ignition on, engine not running.
With a scan tool, actuate the Fuel System test.

NOTE: It may be necessary to use a mechanics stethoscope in the next step.

Listen for fuel pump operation at the fuel tank.

CAUTION: Stop All Actuations.

Q: Does the Fuel Pump operate?

YES: Go To 2
NO: Go To 6

2. FUEL PRESSURE

Turn the ignition off.

WARNING: THE FUEL SYSTEM IS UNDER A CONSTANT PRESSURE (EVEN WITH THE ENGINE OFF). BEFORE TESTING OR SERVICING ANY FUEL SYSTEM HOSE, FITTING OR LINE, THE FUEL SYSTEM PRESSURE MUST BE RELEASED. FAILURE TO FOLLOW THESE INSTRUCTIONS CAN RESULT IN PERSONAL INJURY OR DEATH.

Install a fuel pressure gauge at the engine.
Ignition on, engine not running.
With the scan tool, actuate the ASD Fuel System test and observe the fuel pressure gauge.

NOTE: Fuel pressure specification is 407 KPa ± 34 KPa (59 psi ± 5 psi).

CAUTION: Stop All Actuations.

Choose a conclusion that best matches your fuel pressure reading.

Below Specification
Go To 3

Within Specification
Test Complete.

Above Specification
Replace the fuel filter/fuel pressure regulator. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

3. RESTRICTED FUEL SUPPLY LINE

Turn the ignition off.

WARNING: THE FUEL SYSTEM IS UNDER A CONSTANT PRESSURE EVEN WITH THE ENGINE OFF. BEFORE TESTING OR SERVICING ANY FUEL SYSTEM HOSE, FITTING OR LINE, THE FUEL SYSTEM PRESSURE MUST BE RELEASED.

Raise vehicle on hoist, and disconnect the fuel pressure line at the fuel pump module.
Install special tool #6539 (5/169) or #6631(3/89) fuel line adapter and the fuel pressure gauge between the fuel supply line and the fuel pump module.
Ignition on, engine not running.
With the scan tool, actuate the ASD Fuel System test and observe the fuel pressure gauge.

NOTE: Fuel pressure specification is 407 KPa ± 34 KPa (59 psi ± 5 psi).

CAUTION: Stop All Actuations.

Q: Is the fuel pressure within specification now?

YES: Repair/replace fuel supply line as necessary. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
NO: Go To 4

4. CHECKING FUEL TANK SIPHON HOSE AND FUEL LINE

Turn the ignition off.

WARNING: THE FUEL SYSTEM IS UNDER A CONSTANT PRESSURE (EVEN WITH THE ENGINE OFF). BEFORE TESTING OR SERVICING ANY FUEL SYSTEM HOSE, FITTING OR LINE, THE FUEL SYSTEM PRESSURE MUST BE RELEASED. FAILURE TO FOLLOW THESE INSTRUCTIONS CAN RESULT IN PERSONAL INJURY OR DEATH.

Gain access to the Fuel Pump Module and the Fuel Tank Module. Inspect the following fuel components:
- Fuel line and siphon hose between the Fuel Pump Module and the Fuel Tank Module. Look for disconnected and/or damaged lines or hoses
- Fuel Pressure Regulator not properly seated in the module.
- Debris near or in the modules fuel pick up.

Q: Were the above items in good working condition?

YES: Go To 5
NO: Repair or replace as necessary. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

5. FUEL PRESSURE REGULATOR

WARNING: THE FUEL SYSTEM IS UNDER A CONSTANT PRESSURE (EVEN WITH THE ENGINE OFF). BEFORE TESTING OR SERVICING ANY FUEL SYSTEM HOSE, FITTING OR LINE, THE FUEL SYSTEM PRESSURE MUST BE RELEASED. FAILURE TO FOLLOW THESE INSTRUCTIONS CAN RESULT IN PERSONAL INJURY OR DEATH.

Remove the Fuel Tank Module.
Replace the Fuel Pressure Regulator.
Install the Fuel Pump Module and the Fuel Tank Module.
Retest the fuel pressure.

Q: Is the fuel pressure within specification?

YES: Test complete. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
NO: Replace the Fuel Pump Module. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

6. FUEL PUMP RELAY FUSED B+ CIRCUIT OPEN

Turn the ignition off.
Remove the Fuel Pump Relay from the IPM.
Using a 12 volt test light connected to ground, probe the (A35) Fused B+ circuit at the relay connector.

Q: Does the test illuminate brightly?

YES: Go To 7
NO: Repair the open in the (A35) Fused B+ circuit. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

7. (N1) FUEL PUMP RELAY OUTPUT CIRCUIT OPEN

Turn the ignition off.
Disconnect the Fuel Pump Module harness connector.
Measure the resistance of the (N1) Fuel Pump Relay Output circuit from the relay connector to the fuel pump module connector.

Q: Is the resistance below 5.0 ohms?

YES: Replace the Fuel Pump Relay. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
NO: Repair the open in the (N1) Fuel Pump Relay Output circuit. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test