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Home >> Jeep >> 2023 >> Gladiator Freedom, Part Time T/Case Control >> Repair and Diagnosis >> Engine Performance >> System >> DRIVEABILITY - Diesel - Non-DTC Based Diagnostics >> Diagnosis And Testing >> Checking The Fuel Delivery System >> Diagnostic Test

Diagnostic Test

  1. VISUAL INSPECTION 
    NOTE:

    For best results, perform Fuel Delivery System test with vehicle at room temperature. Extreme cold temperatures can cause inaccurate results.

    NOTE:

    Make sure that the vehicle has at least 1/8 of a tank of fuel before proceeding with this test.

    1. Perform a visual inspection of the fuel system for any signs of a fuel leak.

      Were any visual signs of a leak detected?

      Yes 

      No 

      • Go To  2
  2. CHECK THE SUPPLY SIDE FUEL SYSTEM PRESSURE AND VOLUME AT THE HIGH PRESSURE FUEL PUMP 
    1. Turn the ignition off.
    2. Disconnect the Low Pressure Fuel line at the HPDP inlet.
    3. Connect the (special tool #8978-10, Adapter, Fuel Line)and the 8978-11 adaptor to the HPDP inlet line and pump.
    4. Connect the (special tool #8978A, Decay Tool, Fuel)in-line between the Low Pressure Fuel line and the HPDP adapter.
    5. Close the valve to the collection bottle.
    6. Turn the ignition on.
      NOTE:

      If the scan tool routine is unavailable, it may be necessary to cycle the key or crank the engine to get 15 seconds of fuel pump run time.

    7. Run the Fuel Lift Pump for 15 seconds. Document the pressure reading.
      • Fuel pressure specification - between 4.0 bar (58.0 psi) and 5.9 bar (85.6 psi). 
        NOTE:

        If the pressure reading is too low, skip the volume check and go directly to the results.

    8. Open the valve on the Decay tool to a measuring bottle.
    9. Run the Fuel Lift Pump for 15 seconds. Document the fuel volume collected.
      • Fuel volume specification - minimum of 0.75 liters for 15 seconds. 

      Is the fuel pressure and volume within the listed specifications?

      Fuel Volume and pressure are both within specification 

      • Go To  10

      Fuel Volume is too low 

      • Go To  5

      Fuel pressure is too low 

      • Go To  4

      Fuel pressure is too high 

      • Go To  3
  3. CHECK THE HIGH PRESSURE FUEL PUMP RETURN FLOW 
    1. Turn the ignition off.
    2. Remove the 8978A Fuel Decay Tool and connect the fuel supply line at the High Pressure Fuel Pump.
    3. Disconnect the High Pressure Fuel Pump return line.
    4. Connect the (special tool #8978A, Decay Tool, Fuel)in-line of the HPDP return line using the same adaptors.
    5. Crank or start the engine for 10 - 15 seconds while evaluating the return flow pressure.
      NOTE:

      The return flow should be unrestricted. There should be very little if any pressure on the return flow. Less than 2-3 psi.

      Is the return flow measuring excessive pressure?

      Yes 

      • Check for a restriction in the return line to the Fuel Tank. If the line is not restricted, replace the Fuel Lift Pump in accordance with the Service Information.
      • Perform the PCM VERIFICATION TEST. Refer to PCM VERIFICATION TEST .

      No 

      • Replace the High Pressure Fuel Pump in accordance with the Service Information.
      • Perform the PCM VERIFICATION TEST. Refer to PCM VERIFICATION TEST .
  4. CHECK THE FUEL PRESSURE WITH FUEL DECAY TOOL DEAD HEADED 
    1. Close the fuel system isolation valve on the pressure gauges.
    2. Crank the engine for up to 10 seconds while monitoring the pressure on the inlet gauge.
      NOTE:

      With the fuel flow blocked off the pressure should increase to normal pressure (58.0 psi or above). GEN II systems will increase to max pressure (116 psi).

      Did the fuel pressure increase as described above on the gauge?

      Yes 

      • Replace the High Pressure Fuel Pump in accordance with the Service Information.
      • Perform the PCM VERIFICATION TEST. Refer to PCM VERIFICATION TEST .

      No 

      • Go To  5
  5. CHECK THE SUPPLY PRESSURE AND VOLUME AT FUEL FILTER HOUSING INLET 
    1. Turn the ignition off.
    2. Remove the 8978A Fuel Decay Tool from the High Pressure Fuel Pump line. Reconnect the fuel line.
    3. Disconnect the quick connect fitting at the Fuel Filter inlet line.
    4. Connect the 8978A Fuel Decay Tool with adaptors 8978C-2 and 8978C-3 and check the fuel supply pressure and volume at the inlet side of the Fuel Filter housing using the same method as step 2.
      • Fuel pressure specification - between 4.0 bar (58.0 psi) and 5.9 bar (85.6 psi). 
      • Fuel volume specification - minimum of 0.75 liters for 15 seconds. 

      Is the fuel pressure and volume within the listed specifications?

      Yes 

      • Replace the Fuel Filter in accordance with the service information.
      • Perform the PCM VERIFICATION TEST. Refer to PCM VERIFICATION TEST .

      No 

      • Go To 6 for vehicles that are not equipped with a Fuel Pump Control Module (FPCM).
      • Go To 8 for vehicles equipped with a Fuel Pump Control Module (FPCM).
  6. CHECK THE VOLTAGE DROP OF THE FUEL PUMP MOTOR CIRCUITS 
    1. Turn the engine off.
    2. Reconnect the fuel lines.
      NOTE:

      The Fuel Lift Pump Module harness connector should remain connected to the pump during this test step in order to accurately measure the voltage drop.

    3. Using a voltmeter, back probe the Fuel Pump Motor Feed circuit with the positive lead of the meter at the Fuel Lift Pump Module harness connector.
    4. Back probe the Fuel Lift Pump Ground circuit with the negative lead of the meter at the Fuel Lift Pump Module harness connector.
      CAUTION:

      Use only approved connector back probe tools when back probing a connector so as not to cause damage to the terminals or insulation of the connector. Damage to the terminals can cause poor terminal contact or retention. Damage to the insulation can introduce corrosion due to water intrusion.

    5. Turn the ignition on.
    6. With a scan tool, actuate the Fuel Lift Pump control to ON (100%).
      NOTE:

      The voltage should read the same as battery voltage if there is no resistance in the circuit.

      Is the voltage reading the same as battery voltage +/- 0.2 volt?

      Yes 

      • Check the supply line between the Fuel Lift Pump and the Fuel Filter inlet for a restriction. If the line is not restricted, replace the Fuel Lift Pump in accordance with the service information.
      • Perform the PCM VERIFICATION TEST. Refer to PCM VERIFICATION TEST .

      No 

      • Go To  7
  7. CHECK THE VOLTAGE DROP IN THE FUEL PUMP MOTOR FEED CIRCUIT 
    1. Turn the engine off.
    2. Remove the negative lead of the meter from the Fuel Lift Pump harness connector and connect the lead to a good battery ground.
      NOTE:

      The Fuel Lift Pump Module harness connector should remain connected.

    3. Turn the ignition on.
    4. Using the scan tool, actuate the Fuel Lift Pump control to ON (100%).
    5. Measure the voltage of the Fuel Pump Motor Feed circuit at the Fuel Lift Pump harness connector.

      Is the voltage reading the same as battery voltage +/- 0.2 volt?

      Yes 

      • Repair the Fuel Lift Pump Ground circuit for an open circuit or high resistance.
      • Perform the PCM VERIFICATION TEST. Refer to PCM VERIFICATION TEST .

      No 

      • Repair the Fuel Pump Motor Feed circuit for an open circuit or high resistance.
      • Perform the PCM VERIFICATION TEST. Refer to PCM VERIFICATION TEST .
  8. CHECK THE FUEL PUMP MOTOR GROUND CIRCUIT 
    1. Turn the engine off.
    2. Reconnect the fuel lines.
    3. Disconnect the Fuel Pump assembly harness connector.
    4. Load test the ground circuit at the Fuel Lift Pump Module harness connector.
      NOTE:

      The Fuel Pump grounds through the Fuel Pump Control Module (FPCM) using the FPCM chassis ground.

      Did the ground circuit pass the load test?

      Yes 

      • Go To  9

      No 

      • Repair the ground circuit for an open or high resistance.
      • Perform the PCM VERIFICATION TEST. Refer to PCM VERIFICATION TEST .
  9. CHECK THE FUEL PUMP MOTOR POWER SUPPLY CIRCUIT 
    NOTE:

    There are two steps to checking the power supply for vehicles equipped with an FPCM.

    1. Disconnect the FPCM harness connector.
    2. Measure the resistance of the battery supply circuit between the FPCM and Fuel Pump harness connectors. There should be less than 1.0 Ohms.
    3. Turn the ignition on.
      NOTE:

      The fuel pump relay may need to be actuated or jumped if the relay does not stay on with the ignition on.

    4. Load test the battery supply circuit at the FPCM harness connector. The circuit should be equal to battery voltage.

      Did the battery supply circuit pass both tests?

      Yes 

      • Check the supply line between the Fuel Lift Pump and the Fuel Filter inlet for a restriction. If the line is not restricted, replace the Fuel Lift Pump in accordance with the service information.
      • Perform the PCM VERIFICATION TEST. Refer to PCM VERIFICATION TEST .

      No 

      • Repair the ground circuit for an open or high resistance.
      • Perform the PCM VERIFICATION TEST. Refer to PCM VERIFICATION TEST .
  10. CHECK FUEL QUALITY/CONTAMINATION 
    1. Disconnect the fuel return line at the fuel rail.
    2. Cap the end of the fuel return line with adaptor 8978D-25 to keep debris from entering the system and fuel from leaking out.
    3. Connect a hose to the end of the Fuel Rail return fitting (next to the Fuel Pressure Regulator) and put the hose into a clean container. Crank or start the engine until enough fuel is collected to evaluate.
    4. Check the fuel sample for hard particle debris, cloudiness, color, and off odor. Then let the sample sit in a dust free environment for at least 2 hours to look for any separation.

      Were any problems found?

      Yes 

      No 

      • Go To  11
  11. FUEL INJECTOR LEAK BACK CHECK 
      NOTE:

      The fuel injector leak back can be performed as a static test (engine cranking) or dynamic test (engine running). The procedure and specification for both tests are described below. There should be some leak back return flow for each Fuel Injector during the tests below. If any of the containers is empty after performing the procedure, the Fuel Injector is faulty.

    1. multimedia:A supplement to the article is available.
    2. Turn the ignition off.
    3. Pull up on the center locking tab and disconnect the fuel return hoses at the Fuel Injectors.
    4. Connect the

      (special tool #10493, Tester, Diesel Return Fuel Quantity)

      to all of the Fuel Injectors.

      NOTE:

      For an accurate test result, all of the injectors must be measured at the same time for comparison. The maximum allowable injector return fuel for any injector is 15.0 ml or the 1st graduation of the larger vial in 30 seconds while cranking. Return fuel in excess of this amount would indicate a worn injector in need of replacement.

      NOTE:

      The dynamic procedure is the preferred method of testing. The static procedure should only be performed if the vehicle will not start due to low Fuel Rail Pressure.

      DYNAMIC PROCEDURE 

      • Start the engine and allow it to idle for 120 seconds or until one of the measuring containers is full.
        NOTE:

        If the fuel gets to the point of overflowing the larger graduated vial before the end of the test time, abort the test and evaluate the results.

      • Turn the ignition off.
      • Evaluate the individual return quantities.
        NOTE:

        The fuel injector return flow quantity should not exceed 40.0 ml for any Fuel Injector, however there should be some fuel in each of the containers.

      STATIC PROCEDURE 

      • Crank the engine for 30 seconds.
      • Turn the ignition off.
      • Evaluate the individual return quantities.
        NOTE:

        The fuel injector return flow quantity should not exceed 15.0 ml for any Fuel Injector, however there should be some fuel in each of the containers.

      Is the return fuel quantity collected for any of the Fuel Injectors above specification or empty?

      Yes 

      • Replace the Fuel Injector or Fuel Injectors that were over specification or empty in accordance with the Service Information.
      • Perform the PCM VERIFICATION TEST. Refer to PCM VERIFICATION TEST .

      No 

      • Go To  12
  12. PRESSURE REGULATOR LEAK BACK CHECK 
    1. Turn the ignition off.
    2. Disconnect the fuel return line at the Fuel Pressure Regulator.
    3. Cap the end of the fuel return line with adaptor 8978D-25 to keep debris from entering the system and fuel from leaking out.
    4. Connect a hose to the end of the Fuel Rail return fitting (next to the Fuel Pressure Regulator).
    5. Place the hose into a measurement bottle. The dynamic collection procedure should be used if the engine is capable of running. Otherwise use the static collection procedure.
      NOTE:

      The dynamic procedure is the preferred method of testing. The static procedure should only be performed if the vehicle will not start due to low Fuel Rail Pressure.

      DYNAMIC COLLECTION PROCEDURE 

      • Start the engine and allow it to idle for 10 seconds.
      • Turn the ignition off.
      • Measure the quantity of fuel collected in the bottle.
        NOTE:

        The quantity collected should be between 0 ml and 60 ml.

      NOTE:

      The fuel should be collected during either the static dynamic procedure in the first 10 seconds of engine cranking or running when the fuel quantity solenoid is not energized when fuel is being provided to the high pressure pump at 100%.

      STATIC COLLECTION PROCEDURE 

      • Crank the engine for 10 seconds.
      • Turn the ignition off.
      • Measure the quantity of fuel collected in the bottle.
        NOTE:

        The Fuel Pressure Regulator should be closed during cranking and very little or no fuel should be present (below 10 ml).

      Select the conclusion that best matches the result of the test:

      Static test  result was BELOW 10.0 ml

      Static test  result was ABOVE 10.0 ml

      • Using the wiring diagram as a guide, check the resistance of the Fuel Pressure Regulator circuits. If the resistance is above 2.0 Ohms, repair the high resistance in the wiring. If the resistance is below 2.0 Ohms, replace the Fuel Rail Assembly in accordance with the service information.
      • Perform the PCM VERIFICATION TEST. Refer to PCM VERIFICATION TEST .

      Dynamic test  result was BELOW 30.0 ml

      • Run the cylinder balance test with the scan tool. If a Fuel Injector is out of spec run the cleaning routine. If it is still out of spec, replace the Fuel Injector. If the Fuel Injectors are ok, replace the High Pressure Delivery Pump in accordance with the service information.
      • Perform the PCM VERIFICATION TEST. Refer to PCM VERIFICATION TEST .

      Dynamic test  result was ABOVE 60 ml

      • Using the wiring diagram as a guide, check the resistance of the Fuel Pressure Regulator circuits. If the resistance is above 2.0 Ohms, repair the high resistance in the wiring. If the resistance is below 2.0 Ohms, replace the Fuel Rail Assembly in accordance with the service information.
      • Perform the PCM VERIFICATION TEST. Refer to PCM VERIFICATION TEST .

      Dynamic test  result was BETWEEN 30 ml and 60 ml

      • At this time, the fuel system appears to be operating normally. Check for any Service Bulletins that may apply. It may be necessary to test drive the vehicle under various load conditions while monitoring the fuel pressure actual and target graphs.
      • Perform the PCM VERIFICATION TEST. Refer to PCM VERIFICATION TEST .
  13. CHECK THE FUEL INJECTORS FOR LEAKAGE 
    1. Using the scan tool, crank the engine and monitor the fuel rail pressure actual value. Record the actual values that are achieved.
    2. One at a time, disconnect the Fuel Injector Lines and cap the end of the line with the (special tool #2070000140, Cap, Fuel Rail High Pressure).
    3. Crank the engine and monitor the fuel rail pressure actual value with each Fuel Injector capped off.

      Did the Fuel Rail pressure increase significantly near the target value with one of the Fuel Injectors capped off?

      Yes 

      • Replace the faulty Fuel Injector in accordance with the Service Information.
      • Perform the PCM VERIFICATION TEST. Refer to PCM VERIFICATION TEST .

      No 

      • Replace the High Pressure Delivery Pump in accordance with the service information.
      • Perform the PCM VERIFICATION TEST. Refer to PCM VERIFICATION TEST .
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