LEMON Manuals: Even more car manuals for everyone
Home >> Jeep >> 2014 >> Grand Cherokee Laredo, RWD >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 7 (DRIVEABILITY - Diesel - Non-DTC Based Diagnostics) >> Diagnosis And Testing >> Lack Of Engine Power >> Diagnostic Test

Diagnostic Test

WARNING: This page is about a different variant/trim than selected.
  1. CHECKING FOR PCM DTCS 
    1. Turn the ignition on.
    2. With the scan tool, read the PCM DTCs.

      Are there any DTCs present?

      Yes 

      • Refer to DTC INDEX and perform the appropriate diagnostic procedure.

      No 

      • Go To  2
  2. FUEL SYSTEM LEAK 
    1. 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. Failure to follow these instructions may result in possible serious or fatal injury.

      WARNING:

      Fuel under this amount of pressure can penetrate skin causing possible serious or fatal injury. Inspect for high pressure fuel leaks with a sheet of cardboard. Wear safety goggles and adequate protective clothing when servicing fuel system. Failure to follow these instructions may result in possible serious or fatal injury.

    2. Inspect the entire fuel system for leakage.

      Is there any evidence of leakage?

      Yes 

      • Repair as necessary in accordance with the service information.
      • Perform the PCM VERIFICATION TEST. Refer to appropriate Engine Diagnostic information .

      No 

      • Go To  3
  3. FUEL SYSTEM CONTAMINATION 
    NOTE:

    Mixing any other fuels such as gasoline or kerosine can cause this symptom to occur.

    1. Turn the ignition off.
    2. Inspect the fuel system for contamination.

      Is the fuel contaminated?

      Yes 

      • Repair as necessary in accordance with the service information.
      • Perform the PCM VERIFICATION TEST. Refer to appropriate Engine Diagnostic information .

      No 

      • Go To  4
  4. CHECKING BOOST PRESSURE 
    1. 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.

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

      The Boost Pressure reading should directionally follow (trail) the Boost Pressure Desired/Setpoint reading.

      Does the Boost Pressure reading follow the Boost Pressure Desired/Setpoint reading?

      Yes 

      • Go To  5

      No 

      • Go To  11
  5. CHECKING FUEL PRESSURE 
    1. 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.

    2. 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 

      • Go To  6

      No 

  6. INJECTOR QUANTITY ADJUSTMENT 
    NOTE:

    Each Fuel Injector is labeled with a code. This code determines the injector quantity adjustment. Each Injector code must be programmed into the PCM using the scan tool.

    1. Turn the ignition off.
    2. Refer to the service information to locate each fuel injector label and check for the correct code for each fuel injector in the PCM.

      Are all of the injector codes correct?

      Yes 

      • Go To  7

      No 

      • Using the scan tool, program the correct Fuel Injector code into the PCM.
      • Perform the PCM VERIFICATION TEST. Refer to appropriate Engine Diagnostic information .
  7. ENGINE COMPRESSION 
    1. Start and idle the engine.
    2. With the scan tool, perform the Cylinder Compression Test.

      Does the Cylinder Compression Test indicate low compression in any of the cylinders?

      Yes 

      • Using the service information, repair the engine as necessary to regain proper cylinder compression.
      • Perform the PCM VERIFICATION TEST. Refer to appropriate Engine Diagnostic information .

      No 

      • Go To  8
  8. FUEL INJECTOR 
    NOTE:

    An injector that sticks open can cause this symptom. A sticking injector will cause the engine to miss fire and emit excessive black smoke from the exhaust system.

    1. Start and idle the engine.
    2. With the scan tool, perform the Cylinder Fuel Quantity Correction Test.
      NOTE:

      A problem injector will be indicated by a significant change in correction quantity as compared to the rest of the injectors.

      Are any of the injectors displaying a significant amount of injection quantity correction?

      Yes 

      • Using the service information, remove and inspect the Fuel Injectors for signs of damage or debris that may cause the injector to stick. Sticking injectors may cause the combustion chamber to become black and oil soaked. Replace Injector(s) as necessary.
      • Perform the PCM VERIFICATION TEST. Refer to appropriate Engine Diagnostic information .

      No 

      • Go To  9
  9. CRACKED OR BROKEN FLEX PLATE 
    1. Use the service information to gain access to and inspect for a broken or cracked flex plate.

      Were any problems found?

      Yes 

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

      No 

      • Go To  10
  10. ENGINE DRIVE BELT/CHAIN 
    1. Refer to the service information to ensure the Engine Drive Belt/Chain is installed correctly and the camshaft and crankshaft gears are timed correctly.

      Were any problems found?

      Yes 

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

      No 

      • Test Complete.
  11. CHECK FOR INTAKE AND EXHAUST SYSTEM RESTRICTIONS 
    1. Turn the ignition off.
    2. Inspect the exhaust system for damaged components that could cause exhaust flow blockage.
    3. Inspect all air intake, crankcase vent and turbocharger related hoses/tubes and connections for damage, air leaks or blockage.
    4. Inspect the air filter for excessive dirt, soiling or other problems that may cause restricted air flow.

      Were any problems found?

      Yes 

      • Repair or replace as necessary.
      • Perform the PCM VERIFICATION TEST. Refer to appropriate Engine Diagnostic information .

      No 

      • Go To  12
  12. CHECKING FOR AIR LEAKS 
    NOTE:

    Inspect all air intake and turbocharger related tubes for damage, restriction or poor connection. Any of these conditions can cause a poor performance/lack of power symptom.

    1. Turn the ignition off.
    2. Connect the (special tool #8404C, Kit, EELD And Accessory) to the intake system where possible and begin injecting smoke into the system.
    3. Observe all intake system components for evidence of smoke leakage.

      Is there evidence of smoke leakage?

      Yes 

      • Repair or replace as necessary.
      • Perform the PCM VERIFICATION TEST. Refer to appropriate Engine Diagnostic information .

      No 

      • Check for proper linkage connection between the Boost Pressure Servo Motor and the Turbocharger assembly. Repair or replace as necessary. If OK, refer to the service information and replace the Turbocharger assembly.
      • Perform the PCM VERIFICATION TEST. Refer to appropriate Engine Diagnostic information .
scientia non olet · About LEMON Manuals