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

Vibrations which are related to first-order engine disturbance will usually be evidenced in the following ways:

The most effective way to determine the source of a first-order engine disturbance is to systematically isolate the components (as much as possible) which rotate at engine crankshaft speed.

Isolating the Components

1. Perform the Neutral Run-up Test. Note the RPM at which the vibration is the worst, and the severity of the vibration. Refer to Road Test .
2. Inspect and replace all worn, cracked, or collapsed powertrain mounts.
3. Inspect for and correct any binding or ground-outs in the exhaust system.
4. Inspect for and correct any ground-out conditions in the power steering, air condition, heating, enhanced evaporative emissions and/or any other vehicle systems.
5. If the vehicle is equipped with an automatic transmission, perform the following steps:

5.1.	Mark the location of the transmission torque converter to the flexplate.

5.2.	Disconnect the torque converter from the flexplate and push the torque converter back away from the flexplate. Refer to Flexplate to Torque Converter Bolts in Automatic Transmission.

5.3.	Tie the torque converter with suitable wire to keep it from accidentally engaging with the flexplate.

5.4.	Perform the Neutral Run-up Test again and note if the vibration has been eliminated. Refer to Road Test .

5.5.	With the engine running at idle, observe the flexplate from the side view.

5.6.	If the flexplate shows any wobble of lateral runout, it may be contributing to the vibration, and should be replaced. Refer to Flexplate Replacement in Propeller Shaft.

5.7.	If the vibration IS eliminated by disconnecting the torque converter, reindex the torque converter to the flexplate in the two other possible positions; in an attempt to eliminate the disturbance.

5.8.	If the vibration is still present after reindexing the torque converter, the torque converter should be replaced.

5.9.

If the vibration IS NOT eliminated by disconnecting the torque converter and the flexplate is not bent, inspect the frequency of the vibration at the front and rear of the driveline support assembly (likely caused by excessive propeller shaft runout or imbalance), using the Electronic Vibration Analyzer (EVA).

6. If the frequency of the vibration is strongest along the driveline support assembly; the propeller shaft may have excessive runout or be imbalanced.

6.1.	Remove the driveline support assembly from the vehicle. Refer to Driveline Support Assembly Replacement in Propeller Shaft.

6.2.	Inspect the propeller shaft runout, refer to Driveline Support Overhaul in Propeller Shaft.

7. If the frequency of the vibration is strongest along the engine; the vibration is related to residual engine disturbance. It may be helpful to balance the engine. Whether the balance seems worse at the front or rear of the engine will determine which end requires balancing.

(Replacing the crankshaft (harmonic) balancer, the engine flywheel, or reindexing the torque converter may help

8. Check the engine flywheel (manual transmission) for warping and balance.

(Flywheel should be checked for correct factory indexing. The white paint spot on the flywheel and pressure plate should line up).

Firing frequency is a term used to describe the pulses that an engine creates as each cylinder fires. All engines have a firing frequency -- the object is to prevent these disturbance that the engine firing pulses create, from entering the passenger compartment.

The frequency of these disturbances (engine firing frequencies) will depend on the number of cylinders the engine has. The engine order will always be equal to one-half the number of cylinders. The reason for this is due to the fact that 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 four firing pulses per revolution of the crankshaft, or fourth order.

The following table lists common engine speeds (RPM), along with common vibration classification terms, the first-order frequency (engine disturbance) in Hertz (revolutions per second) associated with each RPM, and the firing frequency order (inherent engine firing frequency) for 4, 6, and 8 cylinder engines also in Hertz associated with each RPM.

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

Isolating the Components

1. Raise and suitably support the vehicle on an inspection-type hoist (either a front-end rack or similar hoist which supports the vehicle at curb height). 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(s) of the vehicle that are excited or responding to the vibration.
4. Closely inspect for witness marks due to a rubbing component.
5. Once an area of the vehicle has been pinpointed, isolate the component, then re-evaluate the vibration.
6. Inspect any vibration excited components and brackets for proper positioning/installation and proper torque; adjust or tighten the component(s) as necessary. If the component positioning/installation and torque are all correct, the component may require replacement.
7. Inspect the for the following conditions and adjust the positioning, repair the condition, or replace components as necessary:

•	Collapsed engine mounts

•	Correct application engine mounts

•	Collapsed transaxle mount

•	Correct application transaxle mount

•	Binding exhaust hangers

•	Check the exhaust hangers both hot and cold (exhaust systems can grow 1 to 2 inches when hot). Try removing the hangers one at a time to isolate.

•	Grounding-out of A/C and/or power steering lines or hoses

•	Ensure the couplings are not tightened with the lines or the hoses are not twisted and binding.

•	Bound or collapsed body mounts; bottomed-out bolts

•	Whipping accessory drive belts

•	Loose accessory unit retaining bolts; accessory unit retaining bolts bottomed-out in dead-end holes

•	Missing bond or fasteners from body panels

•	Add-on aftermarket equipment responding to the vibration

•	Remove the add-on aftermarket equipment, then recheck the condition.

8. The exhaust system and the powertrain mounts are the most likely cause of the vibration being transferred into the passenger compartment. Rebedding the powertrain and aligning the exhaust system properly are very important. Perform the following to rebed a powertrain which may have bound mounts:

8.1.	Loosen the mounts and hangers.

8.2.	Settle the powertrain:

8.2.1.

Start the engine and allow the engine to idle.

8.2.2.

While the engine is idling, shift the transmission from DRIVE to REVERSE.

8.2.3.

Turn OFF the engine.

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

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

A vehicle equipped with a V8 engine demonstrates a vibration that occurs at 40 km/h (25 mph), 64 km/h (40 mph), and at 88 km/h (55 mph). After inspecting the tires and wheels, and not finding any unusual wear or damage, conduct a road test:

Diagnosis of Engine Vibration with the EVA

1. Place the Electronic Vibration Analyzer (EVA) J38792-A 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 to record data:

3.1.	Press RECORD

3.2.	Select a snapshot tag number

(The EVA will begin recording when ENTER is pressed.)

Caution: Road test a vehicle under safe conditions and while obeying all traffic laws. Do not attempt any maneuvers that could jeopardize vehicle control. Failure to adhere to these precautions could lead to serious personal injury and vehicle damage.

4. On a smooth, level road, slowly accelerate until the vibration occurs.
5. Note the vehicle speed (km/h, mph) and engine speed (RPM) at which the disturbance occurs.
6. Press ENTER on the EVA in order to record the vibration data.
7. Perform road test procedures to determine vehicle speed or engine speed sensitivity. Refer to Road Test .

The road test indicates that the vibration is related to the engine speed. The vibration occurs at 1200 RPM and the EVA shows the predominate frequency to be 80 Hz.

Engine Speed Related Calculation

Compare the frequency of the vibration with the engine speed by performing the following:

1. Convert the engine speed in RPM to Hertz, by dividing by 60:

1200 RPM divided by 60 = 20 Hz

2. Playback the information recorded on the EVA during the road test and compare it to the engine speed calculation:

•	Press PLAYBACK, followed by the snapshot tag number.

•	Freeze the display and move through the snapshot frames as needed.

•	The vibration has a frequency of 80 Hz.

•	This frequency does not match the engine speed.

3. The conclusion from this information is that there is NOT a first-order engine disturbance condition.
4. Determine the firing frequency of the engine at 1200 RPM:

•	The engine order is equal to one-half the number of cylinders.

•	The vehicle has a V8, so the ENGINE ORDER is 4.

•	Calculate the firing frequency and convert to Hertz:

-	Engine speed X engine order = firing frequency

-	1200 RPM X 4 = 4800 RPM

-	4800 RPM divided by 60 = 80 Hz

•	The complaint vibration has a frequency of 80 Hz, which matches the engine firing frequency at 1200 RPM.

5. The conclusion from this information is that the vibration IS a result of engine firing pulses.

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

The following table points out various vibration orders which are possible/common in different engine configurations; as well as whether the vibration is considered normal for that engine configuration, or not.

BEFORE attempting to repair any of the disturbances listed in the table, compare the disturbance to another known good vehicle. Some vibration, although it may not be pleasing to the customer, could be normal. It is best to EXPLAIN this UP FRONT, rather than attempt a repair which will likely convince the customer that something is really wrong.

The key to resolving an inherent engine disturbance that is not normal, is to isolate the vibration from the passenger compartment. Follow the same procedures as outlined for the engine firing frequency-related vibrations. (Pay special attention to the powertrain mounts and exhaust system hangers.)

Engine driven accessories that exhibit vibration pose some special challenges. For example, on most vehicles, the accessory drive belts can no longer be removed one at a time in order to isolate the condition to a single component.

Inspect that the vibration is not actually engine firing frequency, excited by the load from an accessory unit:

Isolating the Components

1. Compare the vibrations to a known good vehicle in order to ensure they are abnormal.
2. Remove the accessory drive belts one at a time and check for the presence of the vibration.
3. If the vibration is eliminated, reinstall the belt and operate each accessory one at a time in order to see which component has the most effect on the vibration.

However, because the accessory drive belt drives all of the accessories, one component may affect another (resonance). Be sure of the results.

4. Inspect for bent or misaligned pulleys; this may be a contributing factor to the vibration. Properly align the pulleys or replace any damaged pulleys, as necessary.
5. Inspect the A/C system for overcharging or excessive amounts of oil, which may result in abnormal operating characteristics. Compare these vibrations to a known good vehicle to determine if they are normal or not.