6.6L LB7 Diesel Engine Vibration, Miss

When servicing the vehicle with the VIN you entered, the following diagnosis might be helpful if the vehicle exhibits the described symptoms.

Engine vibration, misfire or run rough; no DTCs.

1. Verify correct oil level and check for the presence of diesel fuel in the engine oil. If diesel fuel is found in the crank case, reference SI document number 866109
2. If the DTCs are present, follow the diagnostic chart for the DTC(s).
3. Review cylinder balance rates in Engine Data 2. Verify they are within specifications 0 plus or minus 4.0 mm (0.16 in). Reference SI document number 796346.
4. Perform fuel injector balance test and note if the vibration or miss is affected. Reference SI document number 796346.
5. Check for loose (60 N·m(44 lb ft ) or missing torque converter bolts. Reference SI document number 703090.
6. Inspect engine mounts or accessories for ground out condition.
7. Remove accessory drive belt and evaluate the concern.
8. If no trouble is found in above, verify the crankshaft pulley is torqued to specification 353 N·m(260 lb  ft).
9. Remove the crankshaft pulley/dampner assembly and inspect for possible sheared pin that aligns pulley to crankshaft. If pin is sheared, the flywheel and torque converter may become separated. The balancer may rotate on the crankshaft causing an out of balance condition.

Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed. If these steps do not resolve the condition, please contact GM TAC for further diagnostic assistance. This diagnostic approach was developed for the vehicle with the VIN you entered and should not be automatically be used for other vehicles with similar symptoms.