Subject: | 6.6L LB7 Engine Vibration Miss or Runs Rough, No DTCs |
When servicing the vehicle with the VIN you entered, the following diagnosis
might be helpful if the vehicle exhibits the described symptoms.
Condition/Concern:
6.6L (LB7) engine vibration, misfire, rough idle, and no DTCs.
Recommendation/Instructions:
- Verify the engine has the correct oil level and check for presence of
diesel fuel in the engine oil. If diesel fuel is found in the crankcase, complete
SI diagnosis for fuel leaks inside of engine.
- If DTCs are present, complete the SI diagnostic chart for the DTC found.
- Use the Tech 2 to monitor the cylinder balance rates. If balance rates
are excessive, complete The SI diagnostics for "Fuel Injector Balance Test with Tech
2".
- Check for loose or missing torque convertor bolts.
NOTE:
DO NOT RUN ENGINE WITH THE TRANSMISSION TORQUE CONVERTER REMOVED. THIS MAY SHEAR
THE CRANKSHAFT BALANCER PIN.
- Inspect the engine mounts and accessories for any ground out conditions.
- Remove the accessory drive belt and evaluate the concern.
- Remove the crankshaft balancer assembly and inspect for a possible sheared
or damaged crankshaft balancer alignment pin. The crankshaft balancer assembly may
rotate on the crankshaft and cause an engine out of balance condition. Verify the
crankshaft balancer is torqued to the proper SI specification.
- If the vehicle has a manual shift transmission, SI diagnosis is inconclusive,
and the above suggestions do not lead to a repair suspect a Dual Mass Flywheel imbalance.
A Dual Mass Flywheel imbalance can cause abnormal injector balance rates, excessive
engine rattle noises, and excessive shift lever vibration. Replace the Dual Mass
Flywheel as needed.
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.
Models
(01 02 03 04 LB7 C2 C3 K2 K3 Chevrolet Silverado and GMC Sierra GMT800) and
(03 04 LB7 C4 C5 D4 D5 E4 E5 Chevrolet Kodiak GMC Topkick GMT560)