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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 appropriate Engine Diagnostic information .

      No 

      • Go To  2
  2. CHECKING SENSOR VALUES WITH THE SCAN TOOL 
    1. Turn the ignition on, engine not running.
    2. With the scan tool, perform the following checks:
      • Check and compare the values of the Ambient Air Temperature Sensor, Coolant Temperature Sensor and Fuel Temperature Sensor with the key on. The values should read approximately equal on a cold engine.
      • Check and compare the values of the Air Inlet Pressure Sensor, Boost Pressure Sensor and Exhaust Differential Pressure Sensor. The sensors should read approximately the same.
      • Check the plausibility of the Accelerator Pedal Position sensors.
    3. If possible, start the engine and check the following:
      • Check the cam/crank synchronization during cranking.
      • Partially open and close the throttle slowly a few times and check and compare the MAF Sensor actual reading against the MAF Sensor set point.
      • Check the plausibility of the temperature and pressure sensors.

      Are the cam and crank synchronized and the sensors reading normal?

      Yes, and combined with a cylinder misfire 

      • Go To  3

      Yes, and combined with any other concern 

      • Go To  6

      No 

      • Repair as necessary.
      • Perform the PCM VERIFICATION TEST. Refer to appropriate Engine Diagnostic information .
  3. SCAN TOOL TEST 
    1. Perform the following tests with the scan tool:
      • Injector Quantity Adjustment for each injector. Look for an injector that is reading noticeably different than the others indicating a faulty injector.
      • Compression Test. The RPM drop in each cylinder should be approximately equal.

      Do any of the cylinders or injectors indicate a problem as compared to the others during the scan tool tests?

      Yes 

      • Evaluate the results of the scan tool tests. If any of the cylinders are found to be performing poorly as compared to the others, check for engine mechanical issues on the suspect cylinder and repair as necessary.
      • If no mechanical issues are found with the engine, Go To  4

      No 

      • Go To  6
  4. STATIC FUEL INJECTOR LEAK BACK CHECK 
    1. Turn the ignition off.
    2. Pull up on the center locking tab and disconnect the fuel return hoses at the Fuel Injectors.
    3. Connect the Bosch Injector Return Flow Meter or equivalent to all of the Fuel Injectors.
    4. Crank the engine for 15 seconds.
    5. Turn the ignition off.
    6. Evaluate the individual return quantities.
      NOTE:

      For an accurate test result, all of the injectors must be measured at the same time for comparison. The maximum allowable injector leak back from any injector is three times the amount collected for the injector with the lowest measured amount (E.G. If the injector with the smallest amount collected is 10 ml, then any injector with more than 30 ml is considered faulty and should be replaced).

      Is the return quantity collected from any of the Fuel Injectors more than three times the Fuel Injector with lowest return quantity collected?

      Yes 

      • Replace the Fuel Injector or Fuel Injectors that were over specification.
      • Perform the PCM VERIFICATION TEST. Refer to appropriate Engine Diagnostic information .

      No 

      • Go To  16
  5. CHECK THE FUEL INJECTOR CIRCUITS FOR OPEN/HIGH RESISTANCE 
    1. Turn the ignition off.
    2. Using the wiring diagram as a guide, check the resistance of the Fuel Injector circuits from the injector to the PCM.

      Do any Fuel Injector circuits measure above 2.0 Ohms?

      Yes 

      • Repair the Fuel Injector circuit(s) that measures above 2.0 Ohms.
      • Perform the PCM VERIFICATION TEST. Refer to appropriate Engine Diagnostic information .

      No 

      • Replace the Fuel Injector in accordance with the service information.
      • Perform the PCM VERIFICATION TEST. Refer to appropriate Engine Diagnostic information .
  6. COMPARE THE FUEL PRESSURE ACTUAL READING AGAINST FUEL PRESSURE SET POINT (TARGET) 
    1. With the scan tool, select and add the fuel rail pressure actual to a graph.
    2. With the scan tool, select and add the fuel rail pressure set point (target) to a graph.
    3. 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.

    4. 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). 

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

      The Fuel Pressure reading appears to mirror close to the Fuel Pressure Set point reading during cranking, idle, and snap acceleration: 

      • Go To  7

      The Fuel Pressure actual reading does not peak during cranking, pressure is too low (below set point) at idle: 

      • If the vehicle is a no start  , Go To  11
      • If the vehicle starts and runs  , Go To  12

      The Fuel Pressure actual reading does not peak during cranking, pressure appears normal (mirrors set point) at idle: 

      • Go To  17

      The Fuel Pressure reading is too high: 

      • Go To  8

      The Fuel Pressure reading is oscillating excessively above and below the Fuel Pressure Set point reading: 

      • 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  12
      • Perform the PCM VERIFICATION TEST. Refer to appropriate Engine Diagnostic information .
  7. CHECKING FUEL QUALITY/CONTAMINATION 
    1. Collect a fuel sample from the vehicle in a clean see through container.
    2. Collect a fuel sample of fresh clean fuel in a clean, transparent container for reference.
    3. Check the vehicle's fuel sample for the following:
      • Check the color of the fuel. Diesel fuel will generally be a yellow color.
      • Allow the fuel to settle and look for cloudiness indicating contamination.
      • Check the volatility of the fuel.
      • Look for a parting line in the fuel sample indicating another type of liquid mixed with the fuel.
      • Look for any signs of debris in the fuel sample.

      Were any problems found?

      Yes 

      • Refer to the service information to replace the fuel in the entire fuel system.
      • Perform the PCM VERIFICATION TEST. Refer to appropriate Engine Diagnostic information .

      No 

      • 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 appropriate Engine Diagnostic information .
  8. CHECK THE SUPPLY SIDE FUEL SYSTEM PRESSURE 
    1. Turn the ignition off.
    2. Disconnect the quick connect fitting at the Fuel Filter outlet line and connect a gauge capable of reading up to 200 psi. in-line.
    3. Crank the engine or start the engine and observe the reading on the fuel pressure gauge.
    4. Turn the ignition off.
      NOTE:

      The fuel pressure specification is between 4.0 bar (58.0 psi) and 5.9 bar (85.6 psi).

      Is the fuel pressure above the listed specifications?

      Yes 

      • If the pressure is reading 8 bar (116 psi) or below, check for a restriction in the line between the Fuel Filter and the HPDP. If no restriction is found, replace the High Pressure Delivery Pump and retest the system.
      • If the pressure is reading above 8 bar (116 psi), replace the Fuel Lift Pump. Check for a restriction in the line between the quick connect fitting and the HPDP. If no restriction is found in the system, replace the High Pressure Delivery Pump.
      • Perform the PCM VERIFICATION TEST. Refer to appropriate Engine Diagnostic information .

      No 

      • Go To  9
  9. CHECKING FOR A RESTRICTION IN THE FUEL RETURN 
    NOTE:

    A leak in the return system due to a hose being off or split could a good indication of a restriction in the fuel return system. Look downstream of the leak for the restriction.

    1. Remove the fuel pressure gauge.
    2. Reconnect the quick connect fitting at the Fuel Filter outlet line.
    3. Disconnect the fuel return hose at the High Pressure Delivery Pump (HPDP) or at the Fuel Rail.
    4. Connect a fuel pressure gauge in-line.
    5. While observing the fuel pressure gauge, start the engine and allow it to come to idle.
      NOTE:

      If there are no restrictions, the return pressure should be below 1.0 bar (14.5 psi).

      Is the return pressure above 3.5 bar (50.76 psi)?

      Yes 

      • Go To  10

      No 

      • Check for high pressure in the fuel supply side.
      • Perform the PCM VERIFICATION TEST. Refer to appropriate Engine Diagnostic information .
  10. CHECKING FUEL RETURN LINE FOR A RESTRICTION 
    1. Remove the fuel pressure gauge.
    2. Disconnect the fuel return line at the Fuel Lift Pump.
    3. Blow regulated shop air through the return line and check for a restriction.

      Was the return line restricted?

      Yes 

      • Repair the restriction in the fuel return line.
      • Perform the PCM VERIFICATION TEST. Refer to appropriate Engine Diagnostic information .

      No 

      • Check for a Fuel Quantity Solenoid that may be sticking in the open position or Fuel Pressure Regulator that may be sticking in the closed position and repair as necessary.
      • Perform the PCM VERIFICATION TEST. Refer to appropriate Engine Diagnostic information .
  11. CHECK THE FUEL RAIL PRESSURE SENSOR 
    1. Disconnect the Fuel Rail Pressure Sensor harness connector.
    2. Attempt to start the engine.

      Does the engine start and run?

      Yes 

      • Using the wiring diagram as a guide, check the resistance of the Fuel Rail Pressure Sensor circuits between the Fuel Rail Pressure Sensor and the PCM. If the resistance is above 2.0 Ohms on any circuit, repair the circuit for high resistance. If the circuits measure below 2.0 Ohms, replace the Fuel Rail Pressure Sensor in accordance with the service information.
      • Perform the PCM VERIFICATION TEST. Refer to appropriate Engine Diagnostic information .

      No 

      • Go To  12
  12. CHECK THE SUPPLY SIDE FUEL SYSTEM PRESSURE AND VOLUME 
    1. Turn the ignition off.
    2. Disconnect the quick connect fitting at the Fuel Filter outlet line and connect (special tool #8978A, Decay Tool, Fuel) in-line.
    3. With the scan tool, actuate the Fuel Lift pump and observe the reading on the fuel pressure gauge.
    4. Open the valve to the measuring bottle and collect fuel for 15 seconds.
    5. Close the valve to the measuring bottle.
    6. Turn the ignition off.
      NOTE:

      The fuel pressure specification is between 4.0 bar (58.0 psi) and 5.9 bar (85.6 psi).

      NOTE:

      The fuel volume specifications is a minimum of 0.75 liters for 15 seconds.

      Is the fuel pressure and volume within the listed specifications?

      Yes, and vehicle is a no start: 

      • Go To  16

      Yes, and vehicle starts and runs: 

      • Go To  17

      No, pressure and/or volume reading is below specification: 

      • Go To  13

      No, pressure reading is above specification: 

      • If the pressure is reading 8 bar (116 psi) or below, check for a restriction in the line between the Fuel Filter and the HPDP. If no restriction is found, replace the High Pressure Delivery Pump and retest the system.
      • If the pressure is reading above 8 bar (116 psi), replace the Fuel Lift Pump and repair the restriction in the line between the quick connect fitting and the HPDP or replace the High Pressure Delivery Pump if no restriction is found and retest the system.
      • Perform the PCM VERIFICATION TEST. Refer to appropriate Engine Diagnostic information .
  13. 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 Fuel Filter outlet 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.

      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 appropriate Engine Diagnostic information .

      No 

      • Go To  14
  14. 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 infiltration.

    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 appropriate Engine Diagnostic information .

      No 

      • Go To  15
  15. 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. With a 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 appropriate Engine Diagnostic information .

      No 

      • Repair the Fuel Pump Motor Feed circuit for an open circuit or high resistance.
      • Perform the PCM VERIFICATION TEST. Refer to appropriate Engine Diagnostic information .
  16. STATIC PRESSURE REGULATOR LEAK BACK CHECK 
    1. Disconnect the fuel return line at the Fuel Rail return fitting (next to the Fuel Pressure Regulator).
    2. Cap the end of the fuel return line to keep debris from entering the system and fuel from leaking out.
    3. Connect a hose to the end of the Fuel Rail.
    4. Place the end of the hose into a measurement bottle.
    5. Crank the engine for 10 seconds.
    6. Turn the ignition off.
    7. Measure the quantity of fuel that was collected from the Fuel Rail.
      NOTE:

      The Fuel Pressure Regulator should be closed during cranking and very little or no fuel should be present.

      Is the quantity of fuel collected from the Fuel Pressure Regulator below 10.0 ml?

      Yes 

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

      No 

      • 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 appropriate Engine Diagnostic information .
  17. DYNAMIC FUEL INJECTOR LEAK BACK CHECK 
    multimedia:A supplement to the article is available.
    1. Turn the ignition off.
    2. Pull up on the center locking tab and disconnect the fuel return hoses at the Fuel Injectors.
    3. Install the Bosch Injector Return Flow Meter or equivalent to the Fuel Injectors.
    4. Start the engine and allow it to idle for 30 seconds or until one of the measuring containers is full.
    5. Turn the ignition off.
    6. Evaluate the individual return quantities.
      NOTE:

      For an accurate test result, all of the injectors must be measured at the same time for comparison. The maximum allowable injector leak back from any injector is three times the amount collected for the injector with the lowest measured amount (E.G. If the injector with the smallest amount collected is 10 ml, then any injector with more than 30 ml is considered faulty and should be replaced).

      Is the return quantity collected from any of the Fuel Injectors more than three times the Fuel Injector with lowest return quantity collected?

      Yes 

      • Replace the Fuel Injector that was over specification.
      • Perform the PCM VERIFICATION TEST. Refer to appropriate Engine Diagnostic information .

      No 

      • Go To  18
  18. DYNAMIC 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. Start the engine and allow it to idle for 10 seconds.
    7. Turn the ignition off.
    8. Measure the quantity of fuel collected in the bottle.

      Is the quantity of fuel collected below 30.0 ml?

      Yes 

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

      No 

      • 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 appropriate Engine Diagnostic information .
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