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Home >> Jeep >> 2021 >> Gladiator Mojave, Part Time T/Case Control, Automatic Trans >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 10 (DRIVEABILITY - Diesel - Non-DTC Based Diagnostics) >> Diagnosis And Testing >> Checking The Fuel Delivery System >> Diagnostic Test

Diagnostic Test

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  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 

      • Repair as necessary
      • Perform the PCM VERIFICATION TEST. Refer to the appropriate service information .

      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 an adapter to the HPDP inlet. (special tool #8978-10, Adapter, Fuel Line)
    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  8

      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 LEAK BACK 
    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.
    5. Crank 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 the appropriate service information .

      No 

      • Replace the High Pressure Fuel Pump in accordance with the Service Information.
      • Perform the PCM VERIFICATION TEST. Refer to the appropriate service information .
  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 or near the Fuel Lift Pump internally regulated pressure of approximately 116 psi.

      Did the fuel pressure increase to the max pressure reading on the gauge?

      Yes 

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

      No 

      • Go To  5
  5. CHECK THE SUPPLY PRESSURE AND VOLUME AT FUEL FILTER HOUSING INLET 
    1. Turn the ignition off.
    2. Remove the (special tool #8978A, Decay Tool, Fuel) 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

      (special tool #8978A, Decay Tool, Fuel)

      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 the appropriate service information .

      No 

      • Go To  6
  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 the appropriate service information .

      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 the appropriate service information .

      No 

      • Repair the Fuel Pump Motor Feed circuit for an open circuit or high resistance.
      • Perform the PCM VERIFICATION TEST. Refer to the appropriate service information .
  8. CHECK FUEL QUALITY/CONTAMINATION 
    1. Collect the fuel in the collection bottle in a clear container.
    2. 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 

      • Repair as needed according to the Diesel Fuel Cleanup portion of the Contamination test procedure. Refer to the appropriate service information .
      • Perform the PCM VERIFICATION TEST. Refer to the appropriate service information .

      No 

      • Go To  9
  9. COMPARE THE FUEL PRESSURE ACTUAL READING AGAINST FUEL PRESSURE SET POINT (TARGET) 
    NOTE:

    If the engine will not start skip this step and continue to Refer to  10.

    1. Verify all fuel lines are connected.
    2. With the scan tool, select and add the fuel rail pressure actual to a graph.
    3. With the scan tool, select and add the fuel rail pressure set point (target) to a graph.
    4. Select merge graphs.
      NOTE:

      For best results when viewing the graphs, set the time increment on the graph to 2.0 seconds and the pressure range to 400 bar (5800 psi) for cranking and idle checks. Change the pressure range to 1600 bar (23, 200 psi) before performing the snap acceleration. The Fuel Pressure reading should closely mirror the Fuel Pressure Set point reading.

    5. While observing the Fuel Pressure Actual reading and the Fuel Pressure Set point on the graph, start the engine and then allow it to idle. After the idle RPM steadies, perform a snap acceleration.
      • The minimum fuel rail pressure needed to start the engine is 120 bar (1740 psi) However, on a normally operating system, the fuel pressure will typically spike up instantly and peak at approximately 310 bar (4496 psi) during cranking. 
      • After starting the engine will typically settle to about 280 bar (4061 psi) at idle. The spec. for minimum fuel rail pressure at idle is 230 bar (3336 psi). 
      • During snap acceleration the pressure reading will typically spike up to between approximately 1500 bar - 1550 bar (21, 756 psi - 22, 481 psi). 

      Was the Fuel Pressure actual reading oscillating excessively above and below the Fuel Pressure Set point reading?

      Yes 

      • Install a clear tube in-line in the fuel supply side, as close to the High Pressure Delivery Pump as possible. Check for signs of air bubbles in the fuel supply system. If air bubbles are present, repair the leak causing the air bubbles getting into the supply side system. If no air bubbles are present, Go To
      • Perform the PCM VERIFICATION TEST. Refer to the appropriate service information .

      No 

      • Go To  10
  10. 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 Bosch Injector Return Flow Meter to all of the Fuel Injectors. (special tool #10493, Tester, Diesel Return Fuel Quantity)
    5. STATIC PROCEDURE 
      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.

      1. Crank the engine for 30 seconds.
      2. Turn the ignition off.
      3. Evaluate the individual return quantities.
      • 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.
    6. DYNAMIC PROCEDURE 
      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.

      1. 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.

      2. Turn the ignition off.
      3. Evaluate the individual return quantities.
      • 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.

      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 the appropriate service information .

      No 

      • Go To  11
  11. 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 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.
    6. STATIC PROCEDURE 
      1. Crank the engine for 10 seconds.
      2. Turn the ignition off.
      3. Measure the quantity of fuel collected in the bottle.
      • The Fuel Pressure Regulator should be closed during cranking and very little or no fuel should be present (below 10 ml).
    7. DYNAMIC PROCEDURE 
      1. Start the engine and allow it to idle for 10 seconds.
      2. Turn the ignition off.
      3. Measure the quantity of fuel collected in the bottle.
      • The quantity collected should be between 0 ml and 60 ml.

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

      Static test result was BELOW 10.0 ml 

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

      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 the appropriate service information .

      Dynamic test result was BELOW 30.0 ml 

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

      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 the appropriate service information .

      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 the appropriate service information .
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