Engine Noise Diagnosis Symptom - Cause/Correction
Exhaust
Symptom(s)
| Cause/Correction
|
Vibrating or Rattling
from the Exhaust System
| Loose and/or misaligned exhaust components. Perform the following steps:
- Align the connections.
- Tighten the connections.
- 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:
| | 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. |
| | 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. |
|
Knocks at Idle Hot
| Inspect the engine for the following conditions:
| | Inspect the tension and replace the drive belt as necessary. |
| • | The A/C compressor or generator bearing |
| | Replace or repair the components as necessary. |
| | Replace the components as necessary. |
| | 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. |
| • | 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: |
| - | 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: |
| - | Thin, diluted, or dirty oil and/or filter |
| - | Excessive main bearing clearance |
| - | Excessive crankshaft end play |
| - | Out-of-round crankshaft journals |
| - | A loose crankshaft pulley |
| - | A loose flywheel or torque converter |
| - | A loose main bearing cap |
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 |
| • | 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 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 |
| • | Excessive piston-to-cylinder bore clearance |
| • | Carbon deposits on top of the piston striking the cylinder head |
| • | Worn or broken piston ring land |
| • | Broken or cracked piston |
| • | Misaligned connecting rods |
| • | 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:
- Operate the vehicle at approximately 32 km/h (20 mph).
- 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 |
| • | 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 |
| • | A broken valve rocker arm bolt |
| • | Loose or worn valve rocker arm attachments |
| • | Missing or improperly positioned lifter guides (roller lifter
engines) |
