2007 Liberty KJ Factory Service Manual 9 - ENGINE

CHECKING THE HIGH-SIDE FUEL SYSTEM

For a complete wiring diagram Refer to Section 8W



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. Refer to the Service Information and Perform the Low/Supply Side Fuel System Test before continuing.


NOTE: This vehicle is not equipped with an in-tank fuel lift pump. The high pressure fuel pump draws (vacuums) the fuel from the fuel tank. Even a very small leak in the fuel supply system between the fuel tank and high-pressure pump can cause driveability problems and dtc's to set.


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.



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

Yes


No

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.


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


No

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 spi 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


No

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.



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

Yes


No

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.

Were any problems found?

Yes


No

6. INJECTOR RETURN VOLUME TEST

Refer the Service Information and perform the Injector Return Volume Test.

Did the Injectors pass the Return Volume Test?

Yes


No

7. FUEL PRESSURE SOLENOID RETURN VOLUME TEST

Refer the Service Information and perform the Fuel Pressure Solenoid Return Volume Test.

Did the Fuel Pressure Solenoid pass the Return Volume Test?

Yes


No