For 1990-2009 cars

Complete the following steps in order to diagnose engine noise:

1. Determine the type of noise.
2. Determine the condition under which the noise exists.
3. Determine the rate and the location of the noise.
4. Compare sounds in other engines in order to ensure that the condition is not normal.

Engine noises are usually synchronized in one of the two following ways:

• | The same as the engine speed

| This indicates that the noise is caused by one of the following components:

- | The crankshaft

- | The connecting rods

- | The pistons

• | One-half of the engine speed

| This indicates that the valve train causes the noise.

### Main Bearing Noise

Listen for any of the following noises:

• | Dull thuds or knocks that occur on every engine revolution

| This noise indicates that the bearings are damaged or worn.

| Any noise that is caused by the bearings is loudest when the engine is under heavy load.

• | An intermittent rap or a knock that is sharper than the noise that is caused by a worn main bearing

| This noise indicates excessive crankshaft end play.

Any of the following conditions may cause main bearing noise:

• | Low oil pump pressure

• | Diluted or dirty oil

• | A dirty filter

• | Excessive main bearing clearance

• | Excessive crankshaft end play

• | Out-of-round crankshaft journals

• | Excessive belt tension

• | A loose crankshaft pulley

• | A loose flywheel

• | A loose torque converter

• | A loose main bearing cap

### Connecting Rod Bearing Noise

A damaged or worn connecting rod bearing causes a knock. The knock occurs at all vehicle speeds.

The noise caused by the connecting rod may sound similar to the noise caused by a piston slap or by loose wrist pins during the early stages of wear.

Connecting rod knock noise becomes louder as the engine speed increases. The connecting rod knock noise is loudest during deceleration.

Any of the following conditions may cause noise in the connecting rod bearings:

• | Excessive bearing clearance

• | A worn crankshaft connecting rod journal

• | Diluted or dirty oil

• | A dirty filter

• | Low oil pressure

• | Crankshaft connecting rod journals that are out-of-round

• | A misaligned connecting rod

• | Improperly torqued connecting rod bolts

• | Incorrect bearing inserts

• | A misaligned bearing half

### Timing Chain and Sprocket Noise

Different noises may be caused by engines that are designed with timing chains and engines that are designed with sprockets.

The most common noise is a high-frequency, light knocking sound.

This sound will generally be the same in intensity when the following conditions exist:

• | The engine is idling

• | The engine is operating at high speeds

• | The engine is operating under load

Any of the following conditions may cause noise in the timing chain and the sprocket:

• | A worn timing chain

• | A misaligned sprocket

• | A damaged sprocket

• | A sprocket that is loose on the shaft

• | Excessive end play in the camshaft or the crankshaft

### Piston Noise

The following noises are similar:

• | Piston noises

• | Piston pin noises

• | Connecting rod noises

A loose pin may cause a sharp double knock when the following conditions exist:

• | The engine is idling.

• | The engine suddenly accelerates then decelerates.

Excessive piston-to-cylinder bore clearance causes a piston slap noise. The noise is similar to a metallic knock. The piston slaps the cylinder wall during the piston stroke. A decrease in noise as the engine warms up indicates piston slap. When the engine is cold, the piston-to-cylinder bore clearance is greater and the piston slap is louder.

The following conditions may cause piston noise:

• | A worn or loose piston pin

• | A worn or loose bushing

• | A pin with an improper fit

• | Excessive clearance between the piston and the cylinder bore (piston slap)

• | Insufficient lubrication

• | Carbon deposits on top of the piston striking cylinder head

• | A worn or broken piston ring land

• | A broken or cracked piston

• | Misaligned connecting rods

• | Worn or damaged rings

• | Worn or out-of-round cylinder walls

• | Excessive ring land clearance

• | Insufficient ring-end gap clearance

• | A piston that is 180 degrees out of position

• | An incorrect piston cam grind

### Valve Mechanism or Valve Train Noise

Either of the following noises may indicate a valve train condition:

• | A light tapping at one-half of the engine speed

• | A light tapping at a varying frequency

These tapping noises increase with engine speed.

Complete the following actions before attempting to evaluate valve train noises:

• | Thoroughly warm up the engine.

| A warm engine will ensure that all of the engine components are at normal state of expansion.

• | Run the engine at various speeds.

• | Close the hood. Sit in the driver seat and listen for any engine noise.

Any of the following conditions may cause valve noise:

• | Broken or weak valve springs

• | Sticking or warped valves

• | Dirty, stuck, worn or faulty valve lifters

• | Damaged or improperly machined camshaft lobes

• | Insufficient or poor oil supply valve train (low oil pressure)

• | Excessive valve stem-to-guide clearance

• | Worn valve guides

### Flywheel Noise (Automatic Transmission)

Notice: Be sure the converter-to-flywheel bolts are not too long. Converter bolts that are too long may dimple the torque converter clutch apply surface causing a shudder condition.

A loose or cracked flywheel produces an irregular thud or click.

Complete the following steps in order to test for a loose or cracked flywheel:

1. Operate the vehicle at approximately 32 km/h (20 mph).
2. Turn off the engine.
3. Listen for a thud noise. A thud may indicate that the flywheel is loose or damaged. This thud is loudest during deceleration.

The sound produced by the following components sound similar to a bearing knock:

• | Loose torque converter-to-flywheel bolts

• | Loose flywheel-to-crankshaft bolts

These conditions produce several raps during quick acceleration on a free running engine. If the idle is smooth when the transaxle is in gear, the noise may not occur. Inspect the torque converter-to-flywheel and flywheel-to-crankshaft bolts before investigating any bearing related knock.