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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 and allow it to idle.
2. With the scan tool, check the air flow reading of the MAF Sensor.
- For an automatic transmission the MAF Sensor should read 3.0-7.0 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. 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 see through 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.

Are there any signs of contamination or poor quality detected?

Yes

- Replace the Fuel Filter and flush the entire fuel system. Replace with clean fuel and operate the vehicle under the conditions that the performance issue was present to verify if condition was fixed.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

No

- Go To 7

7. CHECKING THE FUEL PRESSURE ON SCAN TOOL
1. With the scan tool, graph the fuel pressure set point and actual fuel rail pressure for comparison.
2. Operate the vehicle under the conditions when the performance issue is present.

NOTE: If the conditions exists and the graphs are compared at idle, the fuel deviation should be less than 500 psi ± from the set point. If the conditions exists and the graphs are compared while driving, the fuel deviation should be less than 1500 psi ± from the set point.

3. Compare the two readings during performance issue.

Does the fuel rail pressure deviate more than 500 psi ± from the set point at idle, or more than 1500 psi ± from the set point while driving?

Yes

- Go To 19

No

- Go To 8

8. CHECKING CYLINDER CONTRIBUTION
1. Using the scan tool, perform the Cylinder Cut-Out test procedure.
2. Using the scan tool, perform the Cylinder Balance test procedure.

Do the results indicate a low cylinder?

Yes

- Go To 9

No

- Go To 13

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.
- 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.
- 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 Cylinder Cut-Out test.

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

No

- Go To 16

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

Did the INJECTOR RETURN FLOW TEST pass?

Yes

- Go To 14

No

- Repair as necessary and verify repair. 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.

14. 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 15

No

- Repair the connections as necessary.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

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

Is the valve lash within specification?

Yes

- Go To 16

No

- Adjust the valve lash to specifications.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

16. 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
3. Inspect Turbocharger for wheel clearance and proper wastegate operation.

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 17

17. CHECKING THE EGR SYSTEM
1. Perform the following EGR system checks:
- Look for visible signs (soot streaks) of an external EGR system leak.
- Remove the EGR Outlet Temperature Sensor from the thermostat outlet. Check the outlet for blockage or debris.
- 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 18

18. CHECKING THE EXHAUST AFTERTREATMENT SYSTEM FOR A RESTRICTION
1. Disconnect the Exhaust Aftertreatment 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 diagnostic procedure. Intermittent Condition Test

No

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

19. CHECKING THE FUEL DELIVERY SYSTEM
1. Perform the CHECKING THE FUEL DELIVERY SYSTEM diagnostic procedure.Checking the Fuel Delivery System

Did the CHECKING THE FUEL DELIVERY SYSTEM pass?

Yes

- Check for an intermittent fuel system issue.

No

- Repair the Fuel Delivery System. 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.

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