Checking the High-Side Fuel System

CHECKING THE HIGH-SIDE FUEL SYSTEM

POSSIBLE CAUSES
- Air in fuel system
- Scan tool tests
- Fuel pressure solenoid
- Fuel pressure solenoid return volume test
- Fuel pump
- Fuel system leak
- Injector return volume test

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. Testing and Inspection

Turn the ignition on.

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

With the scan tool, 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 follow (trail) closely to the Fuel Pressure Desired/Setpoint reading.

Q: Does the Fuel Pressure reading follow closely to the Fuel Pressure Desired/Setpoint reading?

YES: Test Complete.
NO: Go To 2

2. 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.
- 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.

Q: Is there any evidence of leakage?

YES: Repair as necessary.
Perform the ECM Verification Test Ver. 1. ECM Verification Test
NO: Go To 3

3. CHECKING FOR AIR IN FUEL SYSTEM
Start the engine.
With the scan tool, 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.

Q: 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. ECM Verification Test
NO: Go To 4

4. FUEL PRESSURE SOLENOID
With the scan tool, compare the Fuel Pressure Setpoint with the Actual Fuel Pressure readings.

NOTE: A sticking Fuel Pressure Solenoid is indicated by Actual Fuel Pressure gradually dropping below the Fuel Pressure Setpoint then suddenly increasing (spiking) above the Fuel Pressure Setpoint.

Q: Does Actual Fuel Pressure gradually decrease then suddenly increase (spike) above the Fuel Pressure?

YES: Replace the Fuel Pressure Solenoid.
Perform the ECM Verification Test Ver. 1. ECM Verification Test
NO: Go To 5

5. SCAN TOOL TESTS
Turn the engine off.
Turn the ignition on.
With the scan tool, select Engine, System Tests and perform the following tests:
- Injector Fuel Correction Test.
- Cylinder Balance test.
- Compression Test.

Q: Were any problems found?

YES: Diagnose and/or repair as necessary.
Perform the ECM Verification Test Ver. 1. ECM Verification Test
NO: Go To 6

6. INJECTOR RETURN VOLUME TEST
Perform the Injector Return Volume Test.

Q: Did the Injectors pass the Return Volume Test?

YES: Go To 7
NO: Replace injector(s) as necessary.
Perform the ECM Verification Test Ver. 1. ECM Verification Test

7. FUEL PRESSURE SOLENOID RETURN VOLUME TEST
Perform the Fuel Pressure Solenoid Return Volume Test.

Q: Did the Fuel Pressure Solenoid pass the Return Volume Test?

YES: Replace the Fuel Pump.
Perform the ECM Verification Test Ver. 1. ECM Verification Test
NO: Replace the Fuel Pressure Solenoid.
Perform the ECM Verification Test Ver. 1. ECM Verification Test