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

Because these vibrations are engine-speed related, they are also normally 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 all 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.

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. Balancing the component or correcting the runout may bring the disturbance to an acceptable level.

Symptoms

Notice: Do not accelerate against the brakes for longer than 10 seconds. Do not overheat the engine or the transmission. Depending on the vehicle design, the engine will only accelerate to a certain point under these conditions. Also, care should be taken during diagnosis as some disturbances may be created during brake torque that normally do not exist.

1. Perform the Neutral run-up test, noting the RPM at which the vibration is the worst, and the most severe. Refer to Types of 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. For automatic transmissions do the following:

4.1.	Mark the location of the torque converter to the flywheel.

4.2.	Disconnect the torque converter from the flywheel and push the converter back from the flywheel.

4.3.	Tie up the converter, away from the flywheel.

4.4.	Perform the Neutral run-up test again. Refer to Types of Road Test . Observe the flywheel.

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.

4.4.1.

Visually inspect from the side for any wobble or lateral runout.

4.4.2.

If any wobble or lateral runout exists, replace the flywheel.

4.5.	If the vibration is eliminated by disconnecting the torque converter, the converter should be re-indexed in three different positions. If the disturbance still exists after this procedure, replace the torque converter. Refer to Transmission Replacement .

4.6.	If the vibration still exists, inspect the harmonic balancer.

4.7.	If the vibration still exists, the problem is related to residual engine imbalance. Refer to Correcting Residual Engine Imbalance below.

1. Install the washers on the harmonic balancer pulley bolts.
2. Replace the bolts with longer bolts of equal hardness as needed.
3. Install the J-nuts on the outer edge of the circular holes in the flywheel.

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

Important: 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 V8 engine will fire cylinders 1, 3, 5, and 7 on the first revolution. Cylinders 2, 4, 6, and 8 will fire on the second revolution. This results in 4 firing pulses per revolution of the crankshaft, or fourth order.

The following are symptoms of engine firing frequency:

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

The key to correcting these types of complaints is to isolate the vibration from the passenger compartment or body. While duplicating the vibration, look closely for witness marks due to a rubbing component. Sometimes adjusting or tightening a component will be all that is necessary. Other times you may have to replace the component. Check for the following?

1. Inspect for collapsed engine mounts.

Replace the mounts as needed. Refer to Engine Mount Inspection for a 3.1L engine or refer to Engine Mount Inspection for a 3.8: engine.

2. Inspect for a collapsed or broken transmission mount.

Replace as needed. Refer to Transmission Mount Replacement .

3. Inspect the exhaust hangers both hot and cold.

Exhaust systems can expand 50-100mm (1-2 inches) when hot.

3.1.	Remove the hangers one at a time.

3.2.	Adjust or replace as needed.

4. Lubricate the manifold flexible coupling (if applicable).
5. Inspect the A/C and P/S lines. Make sure the couplings aren't tightened with the lines or hoses twisted and binding.

5.1.	Isolate the hoses from the body.

5.2.	Install the retainers.

6. Inspect the accessory drive belt for whipping.
7. Inspect the accessory units for loose bolts or bolts bottomed out in dead-end holes.
8. Inspect the body panels for missing or loose welds.
9. Inspect the body mounts for being bound or collapsed.
10. Remove any aftermarket equipment that may complete a transfer path into the passenger compartment.
11. Inspect the exhaust system and powertrain mounts. If necessary, re-bed the engine and align the exhaust system as follows:

11.1.

Loosen the mounts and hangersand ensure the exhaust flexible coupling is free to move.

11.2.

Settle the powertrain by shifting from DRIVE to REVERSE.

11.3.

Tighten all fasteners with the powertrain in the relaxed position.

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

Just like firing frequency, some engine disturbances are the result of normal operation. Some engines can have additional inherent vibration due to the following elements:

Before attempting to repair a disturbance, compare the disturbance to another known good vehicle. Although some vibrations could be normal, the vibrations may not be pleasant to the customer.

The key to resolve 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. Refer to the preceding Engine Firing Frequency-Related Diagnosis in this section.

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 one at a time in order to see which has the most effect on the vibration. However, one component may affect another because the drive belt drives all of the accessories.

Inspect the accessory load to ensure that the load is not exciting the engine firing frequency by completing the following diagnosis:.

Diagnosis

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

3.1.	Install the drive belt.

3.2.	Operate each accessory one at a time in order to see which has the most effect on the vibration.

3.3.	Use the Smart Strobe feature on the EVA to determine which accessory is causing the vibration.

3.3.1.

Clip the inductive pickup of the timing light to the "loop" on the EVA, connect to a 12-volt power source.

3.3.2.

From the Main menu, select Smart Strobe.

3.3.3.

Mark the object you suspect is causing the vibration.

3.3.4.

Enter an initial test point strobe frequency between 10-200 Hz (600-12000 rpm). Press the 0 key to toggle the rpm.

3.3.5.

Press the strobe light trigger as you point the strobe light at the spinning object, then press the EVA Up or Down arrow keys to manually adjust the rpm until only one mark is seen and the object appears stationary. As the test is run, the strobe speed must be manually adjusted to match the actual object rpm.

4. Inspect for accessory load affecting the engine firing frequency.
5. Inspect the pulleys for misalignment or bends. 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 HVAC.
7. Inspect the engine oil level. Add or drain the oil as needed.

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

3.1.	From the Main menu, select Auto Mode.

3.2.	Select the suspected source of the vibration: Engine RPM.

3.3.	Move the cursor to the number of engine cylinders, press Enter.

4. Using the EVA keypad, enter the engine RPM (500-6000 rpm) where the vibration is felt at a maximum level, press Enter.
5. As the test is run, the RPM must be manually adjusted to match the actual engine RPM. To do this, perform the following:

•	Select the incremental step you want to increase/decrease RPM by, press Enter.

•	View the frequency ranges applicable for the RPM selected, press Enter to go to the active data screen or Exit to go back to select the RPM if you are not within a valid range.

•	Press the arrow UP or DOWN key to adjust the on-screen RPM on the active data screen to match the actual engine RPM.

6. Read the test results on the active data display.