For 1990-2009 cars

## Engine Noise Diagnosis Symptom - Cause/Correction

Table 1: | Exhaust
Table 2: | Valve Train
Table 3: | Base Engine

#### Exhaust

Symptom(s) | Cause/Correction
--- | ---
Vibrating or Rattling from the Exhaust System | Loose and/or misaligned exhaust components. Perform the following steps:

1. Align the connections.
2. Tighten the connections.
3. Inspect for damaged exhaust hangers or mounting brackets, and clamps.

Exhaust Leakage and/or Noise | The following conditions may cause exhaust leakage and/or noise:

• | Leakage at the exhaust component joints and couplings

| Tighten the clamps or couplings to the specified torque.

• | Improperly installed or misalignment of the exhaust system

| Align and tighten the exhaust clamps.

• | A cracked exhaust manifold

| Replace the exhaust manifold.

• | A leak between the exhaust manifold or the cylinder head

| Tighten the exhaust manifold to the cylinder head nuts to specifications or replace the exhaust manifold gaskets.

• | A damaged or worn exhaust flex coupling

| Replace the components as necessary.

• | A burned or rusted out exhaust pipe

| Replace the exhaust pipe as necessary.

• | A burned or blown out muffler

| Replace the muffler assembly.

• | A broken or loose exhaust clamp and/or bracket

| Replace the components as necessary.

#### Valve Train

Symptom(s) | Cause/Correction
--- | ---
Intermittent Noise on Idle, Disappearing When Engine Speed is Increased |

• | Dirt in the valve lifter

| Replace the valve lifter if necessary.

• | A pitted or damaged valve lifter check ball

| Replace the valve lifter if necessary.

Noise at Idle or With Hot Oil; Quiet at Higher Engine Speeds or With Cold Oil | High valve lifter leak down rate may cause noise at slow idle or with hot oil. Replace the valve lifter.
Noise at Idle, Louder at Higher Engine Speeds | This noise is not connected with lifter malfunction. The noise is noticeable at 10 to 15 mph in LOW range. The noise is described as a ticking sound. The following conditions may cause noise:

• | A worn valve tip or valve rocker arm pad

• | Excessive valve stem-to-guide clearance

• | Excessive valve seat runout

• | Excessive valve face runout

• | An off-square valve spring

1. | Crank the engine until the noise valve is off its seat.

2. | Rotate the valve spring and valve.

3. | If the noise is corrected, inspect for an off-square valve spring. Replace the valve spring if the valve spring is off-square more than 1.6 mm (0.06 in).

Noise at High Vehicle Speeds, Quiet at Low Speeds | Noise at high vehicle speeds may be caused by the following conditions:

• | High oil level

| An oil level above the FULL mark allows the crankshaft counterweights to churn the oil into foam. When the foam is pumped into the valve lifters, the valve lifters will become noisy. Drain the oil to the proper level.

• | A low oil level

| An oil level below the ADD mark allows the oil pump to pump air. This results in noisy valve lifters. Add oil as necessary.

• | A bent or loose oil pump pickup screen

Noise Regardless of Engine Speed | Inspect for the following conditions:

• | The lubrication system feed to the push rod

• | A worn push rod end ball

• | A bent or damaged push rod

• | A loose or damaged valve rocker arm

If the push rod and the valve rocker arm are OK, trouble in the valve lifter is indicated. Replace the valve lifter.

#### Base Engine

Symptom(s) | Cause/Correction
--- | ---
Knocks on Start-Up but Only Lasts a Few Seconds | Improper oil viscosity Install proper oil viscosity for expected temperatures. Refer to Maintenance and Lubrication.
Knocks Cold and Continues for 2 to 3 Minutes | Cold engine knock usually disappears when the specific cylinder secondary ignition circuit is grounded out. Inspect the engine for the following conditions:

• | Engine flywheel contacting the splash shield

| Reposition the splash shield.

• | Loose or broken crankshaft balancer or drive pulleys

| Tighten or replace the components as necessary.

• | Excessive piston-to-bore clearance

| Inspect and replace the piston components as necessary.

• | Bent connecting rod

Knocks at Idle Hot | Inspect the engine for the following conditions:

• | Drive belt wear

| Inspect the tension and replace the drive belt as necessary.

• | The A/C compressor or generator bearing

| Replace or repair the components as necessary.

• | The valve train

| Replace the components as necessary.

• | Improper oil viscosity

| Install the proper viscosity oil for the expected temperature. Refer to Maintenance and Lubrication for engine oil specifications.

• | Excessive piston pin clearance

| Replace the piston and pin as necessary.

• | Correct connecting rod alignment

| Inspect and replace the connecting rods as necessary.

• | Insufficient piston-to-bore clearance

| Hone the cylinder bore and fit a new piston.

• | The crankshaft balancer for looseness or proper torque

| Replace the worn components.

• | Ensure that the piston pin is not offset to the wrong side.

| Install the piston correctly.

Light Knock Hot | Inspect the engine for the following conditions:

• | Detonation or spark knock

| Refer to Engine Controls.

• | Loose torque converter bolts

• | Exhaust leak at the manifold

| Tighten the bolts and/or replace the gasket.

• | Excessive connecting rod bearing clearance

| Replace the connecting rod bearings as necessary.

Heavy Knock with Torque Applied | Inspect the engine for the following conditions:

• | Broken crankshaft balancer or pulley hub

| Replace the components as necessary.

• | Loose torque converter bolts

| Tighten the torque converter bolts.

• | Accessory drive belts too tight or nicked

| Replace the drive belts as necessary.

• | A cracked flywheel

| Replace the flywheel.

• | Excessive crankshaft main bearing clearance

| Replace the component as necessary.

• | Excessive connecting rod bearing clearance

| Replace the component as necessary.

## Engine Noise Diagnosis General Description

Notice: Some engine noise is characteristic to the design. Compare the sounds in other engines in order to make sure that you are not trying to correct a normal condition.

• | Use the following four elements when diagnosing engine noise:

- | The type of noise

- | Under which operating conditions the noise exists

- | At what rate the noise exists in the engine

- | At what location the noise exists in the engine

• | Compare the sounds in other engines in order to ensure that the noise is not a normal condition.

• | Engine noise is generally synchronized to either engine speed (caused by the crankshaft, connecting rods or pistons) or one-half engine speed (valve train noise). Try to determine the rate at which the noise is occurring.

### Main Bearing Noise

• | Damaged or worn main bearing noise is revealed by dull thuds or knocks which happen on every engine revolution. This noise is loudest when the engine is under heavy load.

• | An intermittent rap or knock sharper than a worn main bearing indicates excessive crankshaft end play.

• | The following conditions cause main bearing noise:

- | Low oil pump pressure

- | Thin, diluted, or dirty oil and/or filter

- | Excessive main bearing clearance

- | Excessive crankshaft end play

- | Out-of-round crankshaft journals

- | Excessive belt tension

- | A loose crankshaft pulley

- | A loose flywheel or torque converter

- | A loose main bearing cap

- | Belt pilling

### Connecting Rod Bearing Noise

A damaged or worn connecting rod bearing will produce a knock under all speeds. During the early stages of wear, connecting rod noise may be confused with piston slap or loose piston pins. Connecting rod knock noise increases in volume with engine speed. This noise is loudest on deceleration.

The following conditions cause connecting rod bearing noise:

• | Excessive bearing clearance

• | A worn crankshaft connecting rod journal

• | Thin, diluted, or dirty oil and/or filter

• | Low oil pressure

• | Crankshaft connecting rod journals out-of-round

• | A misaligned connecting rod

• | Connecting rod nuts not properly torqued

• | The wrong bearing inserts or misaligned bearing half

### Timing Chain and Sprocket Noise

Engines equipped with a timing chain and sprockets may produce noise. The most common noise is a high frequency, light-knocking sound. This sound will generally be the same in intensity whether the engine is idling, operating at high speeds, or under load.

The following conditions may cause timing chain and sprocket noise:

• | A worn timing chain

• | A damaged sprocket

• | A loose sprocket on the camshaft or crankshaft

• | Too much end play in the camshaft or crankshaft

### Piston Noise

Piston pin, piston, and connecting rod noise are hard to separate. A loose piston pin causes a sharp double knock usually heard when the engine is idling, or during sudden acceleration then deceleration of the engine. A piston pin that has been improperly fitted will emit a light ticking noise that is more noticeable with no load on the engine. Excessive piston-to-cylinder bore clearance will cause a piston slap noise. The noise is similar to a metallic knock, as if the piston were slapping the cylinder wall during the stroke.

As with most engine noise, understanding the cause of the noise will help you imagine what the noise sounds like. An indication of piston slap is a decrease in noise as the engine warms up. When the engine is cold, the piston-to-bore clearance is greater and piston slap will be louder. The following conditions may cause piston noise:

• | A worn or loose piston pin

• | Improper pin fit

• | Excessive piston-to-cylinder bore clearance

• | Lack of lubrication

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

• | Worn or broken piston ring land

• | Broken or cracked piston

• | Misaligned connecting rods

• | Worn or damaged rings

• | Excessive ring land clearance

• | Insufficient ring-end gap clearance

• | Piston 180 degrees out of position

• | Incorrect skirt profiles

### Flywheel Noise

Notice: Converter bolts that are too long may dimple the torque converter clutch apply surface and cause a shudder condition.

A loose or cracked flywheel will produce 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. Shut off the engine.

If a thud is heard, the flywheel may be loose or damaged. This type of thud is loudest on deceleration.

Loose torque converter-to-flywheel or flywheel-to-crankshaft bolts will resemble a bearing knock. This condition produces several raps during quick acceleration on a free-running engine. Depending on the idle smoothness, when the transaxle is in gear, the noise may or may not appear.

Inspect the torque converter-to-flywheel and the flywheel-to-crankshaft bolts before attempting to investigate any bearing-related knock.

### Valve Train Noise

A light tapping at one-half engine speed, or any varying frequency, may indicate a valve train problem. These tapping noises increase with the engine speed. Warm up the engine before attempting to judge the valve train noise. This will bring all of the engine components to a normal state of expansion. Run the engine at various speeds and listen for engine noise with the hood closed.

Caution: The following procedure is not recommended on engines with stainless steel exhaust manifolds because manifold temperature will exceed the flash point of the oil causing a fire with possible personal injury.

If the valve mechanism is abnormally noisy, remove the valve rocker arm covers. Use a stethoscope in order to determine which valve train components are causing the noise. The causes of the valve noise include the following conditions:

• | Broken or weak valve springs

• | Sticking or warped valves

• | Bent push rods

• | Dirty, stuck, or worn valve lifters

• | Damaged or improperly machined camshaft lobes

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

• | Excessive valve stem-to-guide clearance

• | Worn valve guides

• | Worn push rods

• | Worn valve rocker arms

• | A broken valve rocker arm bolt

• | Loose or worn valve rocker arm attachments

• | Missing or improperly positioned lifter guides (roller lifter engines)