Checking the High-Side Fuel System

CHECKING THE HIGH-SIDE FUEL SYSTEM

For a complete wiring diagram Consult Diagrams/Electrical





Diagnostic Test

1. CHECKING FUEL PRESSURE

NOTE: The Low/Supply Side Fuel System must be working properly for this test to be valid. Perform the Low/Supply Side Fuel System Test before continuing.

Turn the ignition on.

NOTE: This test requires two people. One person to test drive the vehicle while a technician observes the DRB readings

With the scan tool in Sensors, read and compare the Fuel Pressure (PSI) with the Fuel Pressure Desired/Setpoint (PSI) while test driving the vehicle under various load conditions such as idle, hard acceleration, cruise and deceleration.

NOTE: The Fuel Pressure reading should directionally follow (trail) the Fuel Pressure Desired/Setpoint reading.

Does the Fuel Pressure reading directionally follow the Fuel Pressure Desired/Setpoint reading?

Yes

- Test Complete.

No

- Go To 2

2. FUEL PRESSURE SENSOR CALIBRATION
Turn the ignition on.
With the scan tool, read the Fuel Pressure Sensor volts.
Does the scan tool display between 0.45 and 0.60 volts for the Fuel Pressure Sensor?

Yes

- Go To 3

No

- Check the Fuel Pressure Sensor wiring and connectors for corrosion or poor terminal contact that could cause high resistance. repair as necessary. If wiring and connectors are o.k., replace the Fuel Pressure Sensor.
- Perform the ECM Verification Test Ver. 1. Verification Tests

3. FUEL SYSTEM LEAK
Turn the ignition off.

WARNING: HIGH-PRESSURE FUEL LINES DELIVER DIESEL FUEL UNDER EXTREME PRESSURE FROM THE INJECTION PUMP TO THE FUEL INJECTORS. THIS MAY BE AS HIGH AS 23,200 PSI (1600 BAR). USE EXTREME CAUTION WHEN INSPECTING FOR HIGH-PRESSURE FUEL LEAKS.

WARNING: FUEL UNDER THIS AMOUNT OF PRESSURE CAN PENETRATE SKIN CAUSING PERSONAL INJURY OR DEATH. INSPECT FOR HIGH-PRESSURE FUEL LEAKS WITH A SHEET OF CARDBOARD. WEAR SAFETY GOGGLES AND ADEQUATE PROTECTIVE CLOTHING WHEN SERVICING FUEL SYSTEM.

Inspect the entire fuel system for leakage.
Is there any evidence of leakage?

Yes

- Repair as necessary.
- Perform the ECM Verification Test Ver. 1. Verification Tests

No

- Go To 4

4. CHECKING FOR AIR IN FUEL SYSTEM
Start the engine.
With the scan tool in Sensors, compare the Fuel Pressure Setpoint with the Actual Fuel Pressure readings.

NOTE: If there is air in the fuel system, the Actual Fuel Pressure will oscillate more than 100 psi above and/or below the Fuel Pressure Setpoint.

Does Actual Fuel Pressure oscillate more than 100 psi above and/or below the Fuel Pressure Setpoint?

Yes

- Purge air from the fuel system.
- Perform the ECM Verification Test Ver. 1. Verification Tests

No

- Go To 5

5. FUEL PRESSURE SOLENOID
Turn the ignition off.
Replace the Fuel Pressure Solenoid.
Turn the ignition on.
With the scan tool in Sensors, read and compare the Fuel Pressure (PSI) with the Fuel Pressure Desired/Setpoint (PSI) while test driving the vehicle under various load conditions such as idle, hard acceleration, cruise and deceleration.

NOTE: The Fuel Pressure reading should directionally follow (trail) the Fuel Pressure Desired/Setpoint reading.

Does the Fuel Pressure reading directionally follow the Fuel Pressure Desired/Setpoint reading?

Yes

- Test Complete.

No

- Replace the Fuel Injection Pump assembly.
- Perform the ECM Verification Test Ver. 1. Verification Tests