Engine vibration is usually due to one or more of the following conditions:

Because these vibrations are engine-speed related, they are also usually torque sensitive. These vibrations may appear and disappear at different vehicle or road speeds, but will always appear at the same engine speed.

For example, if a customer states that a vibration is present at 40 km/h (25 mph), 64 km/h (40 mph), and again at 104 km/h (65 mph), and that the symptoms of the vibration are similar at each of these speeds, the vibration is probably engine-speed related. Any disturbance or vibration that is present during the following road tests would be considered engine-speed related:

Any vibration that is present during the neutral coast-down test is not engine-speed related. The engine-related vibrations covered in this diagnosis are engine-speed sensitive only.

Notice: Proper flywheel installation requires carefully WALKING the flywheel onto the crankshaft and stagger-tightening the bolts. Proper torque converter to flywheel installation then requires gradually WALKING the torque converter to be flush with the flywheel, prior to installing the bolts. Do not draw the torque converter to the flywheel with the bolts. If these precautions are not followed, warping or bending of the flywheel and/or damage to the transmission torque converter may result.

Engine imbalance is a condition that exists when a component that rotates at crankshaft speed is either unbalanced or has excessive runout. In rare cases, the crankshaft may be unbalanced. In any case, balancing the component or correcting the runout may reduce the disturbance to an acceptable level.

1. Perform the neutral run-up test, noting the RPM at which the vibration is the worst, and the severity. Refer to Road Test .
2. Inspect all powertrain mounts. Repair or replace as needed.
3. Inspect for any bindings or ground-outs in the exhaust system.
4. Matchmark the torque converter and the flywheel.
5. Disconnect the torque converter from the flywheel.
6. Tie up the converter, away from the flywheel.
7. Perform the neutral run-up test again.

•	If the flywheel shows any wobble or lateral runout, replace the flywheel. Refer to Engine Flywheel Replacement in Engine Mechanical-3.8 L or Engine Flywheel Replacement in Engine Mechanical-5.7 L.

•	Re-index the torque converter in three different positions. If the disturbance still exists, replace the torque converter.

8. If the vibration still exists, inspect the propeller shaft runout.
9. If the vibration still exists, inspect the harmonic balancer.
10. If the vibration still exists, the problem is related to residual engine imbalance. Refer to the procedure below.

Firing frequency is a term used to describe the pulses created as the engine fires in each cylinder. All engines have a firing frequency. The intention here is to keep these disturbances from entering the passenger compartment. Initially, inspect for the following conditions:

The frequency of these disturbances will depend on the number of cylinders. The engine order will always be equal to one-half the number of cylinders. This is because a four-stroke engine requires two complete revolutions of the crankshaft in order to fire all of the cylinders.

For example, a V6 engine will fire cylinders 1, 3, and 5 on the first revolution. Cylinders 2, 4, and 6 will fire on the second revolution. This results in three firing pulses per revolution of the crankshaft.

1. Place the EVA vibration sensor on the seat track rail with the UP label facing upward.
2. Plug the EVA into a 12 volt power supply.
3. Prepare the EVA for data recording:

3.1.	Press RECORD

3.2.	Select a snapshot tag number

3.3.	Press ENTER in order to begin recording

4. Slowly accelerate until the vibration occurs.
5. Note the vehicle speed and the engine RPM where the disturbance occurs.
6. Press ENTER on the EVA in order to record the vibration data.
7. Perform the road test diagnoses in order to determine engine-speed or vehicle-speed sensitivity. Refer to Road Test .

The key to correcting these types of complaints is to isolate the vibration from the passenger compartment or the body.

1. Raise and suitably support the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.

Caution: One or more of the following guidelines may apply when performing specific required tests in the work stall:

•	When a test requires spinning the drive wheels with the vehicle jacked up, adhere to the following precautions:

-	Do not exceed 56 km/h (35 mph) when spinning one drive wheel with the other drive wheel stopped. This limit is necessary because the speedometer indicates only one-half the actual vehicle speed under these conditions. Personal injury may result from excessive wheel spinning.

-	If all of the drive wheels are spinning at the same speed, do not exceed 112 km/h (70 mph). Personal injury may result from excessive wheel spinning.

-	All persons should stay clear of the rotating components and the balance weight areas in order to avoid possible personal injury.

-	When running an engine in the repair stall for an extended period of time, use care not to overheat the engine and the transmission.

•	When a test requires jacking up the vehicle and running with the wheels and brake rotors removed, adhere to the following precautions:

-	Support the suspension at normal ride height.

-	Do not apply the brake with the brake rotors removed.

-	Do not place the transmission in PARK with the drive axles spinning.

-	Turn Off the ignition in order to stop the powertrain components from spinning.

•	When running an engine in the work stall, use the exhaust removal system to prevent breathing dangerous gases.

2. Attempt to duplicate the vibration.
3. While the vibration is present, find the area of the vehicle affected by the vibration.
4. Inspect for witness marks caused by rubbing components.
5. Isolate the component and re-evaluate the vibration.
6. Inspect for proper torque on the affected component. Tighten as needed.
7. If the vibration still exists, follow the procedure below.

1. Inspect for collapsed engine mounts.

Replace as needed. Refer to Engine Mount Replacement in Engine Mechanical - 3.8 L or Engine Mount Replacement in Engine Mechanical - 5.7 L.

2. Inspect for a collapsed or broken transmission mount. Replace as needed. Refer to Transmission Support and Mount Assembly Replacement in Manual Transmission - M49, Transmission Support and Mount Assembly Replacement in Manual Transmission - MM6 or Transmission Support Replacement in Frame and Underbody.
3. Inspect the exhaust hangers.

•	Exhaust systems can expand one to two inches when hot.

•	Remove the hangers one at a time.

•	Adjust or replace the exhaust hangers as needed.

4. Inspect the A/C and P/S lines.

•	Isolate the hoses from the body.

•	Install the retainers.

5. Inspect the drive belt for the proper tension.
6. Inspect the accessory unit fasteners for damage or looseness.
7. Inspect the body panels for missing or loose welds.
8. Remove any aftermarket equipment that may complete a transfer path into the passenger compartment.
9. Inspect the exhaust system and powertrain mounts. Re-bed the engine and align the exhaust system as follows if needed:

•	Loosen the mounts and hangers.

•	Tighten all fasteners with the powertrain in the relaxed position.

Some residual vibrations may be normal. Compare the vibrations with a similar vehicle to get a feel for what is commercially acceptable, preferably with the customer present. Also, refer to bulletins for updates on the use of mass damper weights for specific applications.

Just as with firing frequency, some engine disturbances are the result of normal operation. Some engines can have additional inherent vibration due to the cylinder arrangement, the design, or the firing order.

Before attempting to repair a disturbance, compare the disturbance to another, known good, vehicle. Some vibrations could be normal though they may not be pleasing to the customer.

The key to resolving an inherent engine disturbance is to isolate the vibration from the passenger compartment. Follow the same procedures as outlined for the engine firing-frequency related vibrations.

Engine driven accessories that exhibit vibration pose some special challenges. For example, the drive belts can no longer be removed one at a time in order to isolate the condition. If removing the belt eliminates the vibration, reinstall the belt and operate each accessory individually in order to determine which has the most effect on the vibration. However, one component may affect another because the drive belt drives all of the accessories.

Verify that the accessory load is not affecting the engine firing frequency.

Diagnosis

1. Compare the vibrations to a known good vehicle in order to ensure they are abnormal.
2. Remove the drive belt.
3. If the vibration stops, perform the following steps:

3.1.	Install the drive belt.

Important: The drive belt drives all of the engine accessories. Therefore, one component may affect another.

3.2.	Operate each accessory individually in order to determine which has the most effect on the vibration.

4. Test for the accessory load affecting the engine firing frequency.
5. Inspect the pulleys for misalignment or lateral runout. Repair or replace as needed.
6. Inspect the A/C system for overcharging. Evacuate and recharge as needed. Refer to Refrigerant Recovery and Recharging in Heating, Ventilation and Air Conditioning.
7. Inspect the engine oil level. Add or drain oil as needed.