Symptom
| Cause
|
When diagnosing engine noise complaints use the following steps to isolate
the source of the engine noise:
- Determine the type of the noise.
This may include a light rattle, tapping or low rumble or knock.
- Verify the exact operating condition when the noise occurs.
This would include ambient engine temperature, engine warm-up time,
engine operating temperature, and engine RPM.
- Isolate the rate when the noise occurs.
Generally speaking, engine noises are timed to either engine speed (crankshaft,
flywheel, connecting rods, balancer, or pistons and related components) or
one-half engine speed (valve train noise such as rocker arms, valve lifters,
and timing chain).
- Compare the engine sounds to a known good engine to prevent trying
to fix a noise that is normal.
|
Noise on Start-Up but Lasts a Few Seconds
| The following condition(s) may produce engine
knocks on initial start-up, but only last a few seconds:
| • | Improper oil viscosity. |
| • | Install proper oil viscosity for expected temperatures. Refer
to Maintenance and Lubrication |
|
Knocks Cold and Continues for 1 to 2 Minutes
|
| • | Engine flywheel contacting the splash shield. Reposition the splash
shield. |
| • | Loose or broken crankshaft balancer or drive pulleys. Tighten
or replace as necessary. |
| • | Excessive piston to bore clearance. Replace the piston. |
| • | Cold engine knock usually disappears when the specific cylinder
secondary ignition circuit is grounded out. Cold engine piston knock which
disappears in 1.5 minutes should be considered acceptable. |
|
Intermittent Noise on Idle, Disappearing When Engine Speed is Increased
|
| • | Dirt in the lifter. Replace the valve lifter if necessary. |
| • | A pitted or damaged valve lifter check ball. Replace the valve
lifter if necessary. |
|
Valve Train Noise (Rattle/Tapping)
| The following conditions may cause valve train noise:
| • | Loose valve rocker arm attachments |
| • | Worn valve rocker arm and/or pushrod. |
| • | Worn or damaged valve rotators. |
| • | Sticking valves. Inspect the valves. |
| • | Worn, dirty or faulty valve lifters. |
| • | Worn or faulty camshaft. Replace the camshaft. |
| • | Worn or faulty oil pump |
| • | Bent, broken, or damaged timing chain sprocket teeth |
| • | Worn valve guides. Repair as necessary. |
| • | Oil overfull causing foaming of oil. |
|
Knocks at Idle Hot (Rumble/Knocking)
|
| • | Inspect the drive belt for wear. Check the tension and/or replace
as necessary. |
| • | Inspect the A/C compressor or generator bearing. Replace or repair
as necessary. |
| • | Inspect the valve train. Replace the parts as necessary. |
| • | Inspect for improper oil viscosity. Install proper viscosity oil
for expected temperature. Refer to Maintenance and Lubrication for engine
oil specifications. |
| • | Inspect for excessive piston pin clearance. Replace the piston
and pin as necessary. |
| • | Inspect the connecting rod alignment. Check and replace the rods
as necessary. |
| • | Inspect for insufficient piston-to bore clearance. |
| • | Bore, Hone, and fit the new piston. |
| • | Inspect the crankshaft balancer for looseness. Torque and/or replace
the worn parts. |
| • | Ensure that the piston pin is not offset to the wrong side. Install
the correct piston. |
|
Light Knock Hot
|
| • | Detonation or spark knock. Check operation of EST or ESC. Refer
to Engine Controls. |
| • | Loose torque converter bolts. |
| • | Exhaust leak at the manifold. Tighten the bolts and/or replace
the gasket. |
| • | Excessive rod bearing clearance. Replace bearings as necessary. |
|
Noise at Slow 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 High Vehicle Speeds, Quiet at Low
Speeds
| Noise
at high vehicle speeds may be caused by the following conditions:
| • | High oil level. Oil levels above the FULL mark allows the crankshaft
counterweights to churn the oil into foam. When foam is pumped into the valve
lifters, they will become noisy since a solid column of oil is required for
proper operation. Drain the oil to the proper level. |
| • | A low oil level. Oil below the ADD mark allows the oil pump to
pump air at high speeds, which results in noisy valve lifters. Add oil as
necessary. |
| • | Oil pan bent up against the oil pump pickup screen. |
| • | Oil pump pickup screen bent or loose. |
|
Noise Regardless of Engine Speed
|
| • | Incorrect valve adjustment leading to noise regardless of engine
speed. Check valve lash. |
| • | Excessive valve lash may cause engine noise. Check for valve lash
by turning the engine so that the piston in that cylinder is on TDC of the
firing stroke. If the valve lash is present, the pushrod can be freely moved
up and down a certain amount with the valve rocker arm held against the valve. |
| • | Excessive valve lash may be caused by the following conditions: |
| - | A worn pushrod upper end ball. Replace the pushrod and the valve
rocker arm. |
| - | Improper lubrication of he pushrod. Replace the pushrod and the
valve rocker arm. |
| • | Check the lubrication system feed to the pushrod |
| - | A loose or damaged valve rocker arm. |
| - | If the pushrod and valve rocker are OK, trouble in the valve lifter
is indicated. Replace the valve lifter. |
|
Vibrating or Rattling from Exhaust System
| Vibration or ratting from the exhaust system
may be caused by loose and/or misaligned exhaust components. Align, then tighten
the connections. Check for damaged hangers or mounting brackets and clamps.
|
Exhaust Leakage and/or Noise
| Exhaust leakage and/or noise may be caused by the following
conditions:
| • | 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,
then tighten the exhaust clamps. |
| • | A cracked or broken 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 and bolts to specifications. |
| • | Damaged or worn exhaust seals. Replace 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 as necessary. |
|
Heavy Knock with Torque Applied
|
| • | Broken balancer or pulley hub. Replace parts as necessary. |
| • | Loose torque converter bolts. |
| • | Accessory belts too tight or nicked. Replace and/or tension to
specifications as necessary. |
| • | Excessive main bearing clearance. Replace as necessary. |
| • | Excessive rod bearing clearance. Replace as necessary. |
|
