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Checking Engine Misfire / Runs Rough / Performance Test






CHECKING ENGINE MISFIRE / RUNS ROUGH / PERFORMANCE TEST

Theory of Operation

There are two purposes to this diagnostic test. The first purpose is to try to determine whether an engine misfire or rough running condition can be narrowed down to a specific cylinder or if it is due to a fuel, air handling, or exhaust system issue. The second purpose is to help the technician follow the correct path to diagnose and completely repair the system at fault.

1. RELATED TSBs

NOTE: If there are DTCs present in the PCM, TCM, or ABS Modules, repair the DTCs before proceeding.

1. Check for any TSBs or, ECM or CCN software updates that may relate to customer's complaint.
2. Follow the appropriate diagnostic procedure in the TSB.

Is vehicle repaired?

Yes

- Repair complete.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

No

- Go To 2

2. VISUAL INSPECTION
1. Perform an inspection of the following:
- Verify there are no external fuel or coolant leaks.
- Verify the oil level. An excessively high or low oil level may cause a performance issue.
- Visually inspect the air filter for a restriction.
- Verify that the battery voltage is between 12.5 and 14.0 Volts when running.
- Verify that there are no Non-OEM engine modifications installed on the vehicle.
- Verify proper fuel level.
- Listen for any obvious intake or exhaust leaks.

Were any of the above conditions found?

Yes

- Repair as necessary and verify repair.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

No

- Go To 3

3. CHECKING MASS AIR FLOW SENSOR OPERATION
1. Start the engine, allow it to reach operating temperature and then idle for five minutes.

NOTE: This is how long it takes for the EGR Valve to close.

2. With the scan tool in Data Display, verify that the EGR Valve is at 0%.
3. With the scan tool, read the MAF Sensor value:
- For an automatic transmission the MAF Sensor should read 3.0 - 6.75 lb/min at idle.
- For a manual transmission the MAF Sensor should read 3.5 - 7.5 lb/min at idle.

Is the MAF Sensor reading within specification?

Yes

- Go To 4

No

- Replace the MAF Sensor.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

4. CHECKING THE ACCELERATOR PEDAL POSITION SENSORS
1. Turn the engine off, ignition on.
2. With the scan tool, graph the APP 1 and APP 2 sensors while operating the accelerator pedal smoothly through a full range of motion and back.

Does the Accelerator Pedal Position Sensors show any signs of an erratic signal through the range of motion?

Yes

- Diagnose and repair the Accelerator Pedal Position Sensors.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

No

- Go To 5

5. CHECKING THE VEHICLE SPEED AND ENGINE SPEED
1. With the scan tool, graph the Vehicle Speed Sensor and RPMs.
2. Operate the vehicle under the condition when the performance issue is present.
3. Compare the two readings for plausibility.

Do the two readings appear plausible?

Yes

- Go To 6

No

- Diagnose the Vehicle Speed Sensor and/or the Engine Speed Sensor.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

6. CHECKING FUEL QUALITY/CONTAMINATION
1. Check the quality of the fuel using the DIESEL FUEL CONTAMINATION TEST PROCEDURE. Fuel Contamination

Was any contamination detected?

Yes

- Perform the appropriate repair according to the testing and cleaning procedure.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

No

- Go To 7

7. CHECKING CYLINDER CONTRIBUTION
1. Using the scan tool, navigate to Miscellaneous Functions perform the Fuel System Run Up test procedure.

NOTE: This test will take approximately 270 seconds to complete. The PCM will cut out each individual Fuel Injector three times and calculate the delta RPM change. Based on the delta RPM change, the test will indicate a bad cylinder based on the limits that have been set. When the test is complete, the engine will return to idle.

Do the results indicate that a cylinder is out of speck?

Yes

- Go To 8

No

- Go To 13

8. INJECTOR RETURN FLOW TEST
1. Injector Return Flow Test Perform the INJECTOR RETURN FLOW TEST diagnostic procedure.

Did the INJECTOR RETURN FLOW TEST pass?

Yes

- Go To 9

No

- Repair as necessary and verify repair by performing the Fuel System Run Up test procedure again. Inspect and clean any soot fouling in the Air Handling and Exhaust systems as needed.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

9. CHECKING FUEL INJECTOR AND VALVE COVER HARNESS TERMINALS
1. Turn the ignition off.
2. Visually check the valve cover connectors and Fuel Injector terminals for loose connections or damaged threads.
3. Check the torque of the Fuel Injector nuts.

NOTE: The Fuel injector nuts should be torqued to 8.8 in/lbs.

Are the Fuel injector nuts torqued correctly and the connections and terminals good?

Yes

- Go To 10

No

- Repair the connections as necessary. Verify repair by performing the Fuel System Run Up test procedure again.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

10. CHECKING VALVE LASH
1. Check the valve lash adjustment on the suspect cylinder or cylinders.

Is the valve lash within specification?

Yes

- Go To 11

No

- Adjust the valve lash to specifications and verify repair by performing the Fuel System Run Up test procedure again.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

11. COMPRESSION CHECK
1. Perform a manual compression check of the cylinder.

Is the compression within specification?

Yes

- Go To 12

No

- Perform a cylinder leak down test to determine if the low compression is caused a by piston or cylinder head/valve condition and repair as necessary. Inspect and clean any soot fouling in the Air Handling and Exhaust systems as needed.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

12. FUEL INJECTORS
1. Change the Fuel Injector with a Fuel Injector from another good cylinder.
2. With the scan tool, perform the Fuel System Run Up test procedure.

Did the performance issue follow the Fuel Injector?

Yes

- Replace the Fuel Injector and check for fuel contamination. If fuel is found to be contaminated, determine the point of entry of the contamination and repair. Inspect and clean any soot fouling in the Air Handling and Exhaust systems as needed. Verify repair by performing the Fuel System Run Up test procedure again.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

No

- Go To 14

13. PERFORM THE HIGH PRESSURE FUEL SYSTEM TEST
1. Using the scan tool, navigate to System Tests and perform the High Pressure Fuel System test procedure.

NOTE: The High Pressure Fuel System test routine commands engine speed and rail pressure. The routine will evaluate the amount of time it takes to build and reduce pressure in the system by increasing and decreasing the rail pressure set points at different engine speeds. When the test is complete, the engine will stall as it measure the time it takes to go from 26,107 psi (1800 bar) to 0 psi. This routine is designed to test certain components of the fuel system and may reduce the time needed to diagnose the system.

Did the vehicle pass the High Pressure Fuel System test procedure?

Yes

- Go To 14

No

- Perform the CHECKING THE FUEL DELIVERY SYSTEM diagnostic procedure and continue troubleshooting the fuel system starting at the results in test step 4. Checking the Fuel Delivery System.

14. CHECKING THE INTAKE SYSTEM
1. Check for inlet restriction, inspect air filter for excessive dirt/debris. Verify air intake lines are not kinked or restricted.
2. Perform the CHECKING THE INTAKE AIR SYSTEM PRESSURE diagnostic procedure. Intake Air System Pressure Test

Were any problems found?

Yes

- Repair as necessary. Inspect and clean any soot fouling in the Air Handling and Exhaust systems as needed.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

No

- Go To 15

15. CHECKING THE EGR SYSTEM
1. Perform the following EGR system checks:
- Look for visible signs (soot streaks) of an external EGR system leak.
- Remove EGR Crossover tube from EGR Cooler and EGR Valve. Inspect the tube for a restriction.
- Verify EGR Cooler is not leaking. Check for coolant in EGR plumbing, engine overheat fault codes, and low coolant level.
- Check the Air Intake Grid Heater for excessive soot build up or restriction.

Were any problems found?

Yes

- Repair as necessary. Inspect and clean any soot fouling in the Air Handling and Exhaust systems as needed.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

No

- Go To 16

16. CHECKING THE EXHAUST AFTER TREATMENT SYSTEM FOR A RESTRICTION
1. Disconnect the exhaust after treatment system at the outlet of the Turbocharger.

Is the performance issue still present?

Yes

- It is possible that the condition is being caused by an intermittent condition. Perform the INTERMITTENT CONDITION - 6.7L diagnostic procedure. Intermittent Condition Test

No

- Inspect the components in the exhaust after treatment system for a restriction. Replace the restricted component.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

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