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, PCM 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 THE AIR FILTER
1. Visually inspect the Air Filter for modifications, or excessive dirt or debris causing a restriction.

Were any issues found?

Yes

- Replace the Air Filter.
- Go To 4

No

- Go To 4

4. 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 5

5. CHECKING CYLINDER CONTRIBUTION
1. Using the scan tool, navigate to Miscellaneous Functions and perform the Injector Kill test procedure.

Do the results indicate that a cylinder is low?

Yes

- Go To 6

No

- Go To 11

6. 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 7

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.

7. 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 8

No

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

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

Is the valve lash within specification?

Yes

- Go To 9

No

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

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

Is the compression within specification?

Yes

- Go To 10

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.

10. 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 15

11. CHECK THE FUEL DELIVERY SYSTEM
1. Perform the CHECKING THE FUEL DELIVERY SYSTEM diagnostic procedure. Checking The Fuel Delivery System.

Were any fuel system issues found?

Yes

- 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.

No

- Go To 12

12. CHECK THE ENGINE PRESSURE SENSORS

NOTE: Perform steps 5, 6, and 7 of the 6.7L Cummins Diagnostic Worksheet. Star Center must be contacted before worksheet steps 5, 6, and 7 can be completed.

1. Turn the engine off, ignition on.
2. With the scan tool, compare the Barometric Sensor reading and the Exhaust Pressure Sensor reading.

Are the two readings equal?

Yes

- Go To 13

No

- Compare the two readings to the Inlet Air Pressure Sensor reading. Replace the sensor that does not match the Inlet Air Pressure Sensor.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

13. CHECKING MASS AIR FLOW SENSOR OPERATION
1. Turn the ignition on, engine not running.
2. With the scan tool, read the MAF Sensor value:
- The MAF Sensor should be reading close to 0.01lb/min.

3. 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.

4. With the scan tool in Data Display, verify that the EGR Valve is at 0%.
5. 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 14

No

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

14. CHECK CRANKCASE FILTER
1. Verify proper Crankcase Filter operation.

Were any problems found?

Yes

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

No

- Go To 15

15. 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. Intake Air System Pressure Test Perform the CHECKING THE INTAKE AIR SYSTEM PRESSURE diagnostic procedure.
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 16

16. 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

- If the soot inside the EGR Crossover Tube is oily, inspect the Turbocharger for leaking oil into the intake system. If Turbo is leaking, replace the Turbo. If Turbo is not leaking, clean the Crossover Tube, remove and clean the EGR Valve and EGR Cooler.
- Go To 17

No

- Go To 17

17. CHECK THE EXHAUST AFTER TREATMENT SYSTEM FOR A RESTRICTION
1. Perform the AFTERTREATMENT INSPECTION GUIDELINE procedure. Initial Inspection and Diagnostic Overview.

Were any problems found during the inspection?

Yes

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

No

- Perform the DIESEL FUEL VALIDATION procedure. Component Tests and General Diagnostics. If the vehicles passes the validation, the vehicle is operating properly. If the vehicle fails the validation, the issue was missed during diagnostics.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.