Symptom
| Cause
|
There are four steps
to diagnosing engine noise. You must determine the following:
| For example, is the noise a light rattle/tapping or a low rumble/knocking? |
• | The exact operating condition under which the noise exists |
| Note factors such as the ambient temperature, the amount of engine warm-up
time, the engine temperature, engine RPM's, and other specifics. |
• | At what rate the noise occurs, and at what location in the engine |
| Remember, engine noises are generally synchronized 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). Try to determine the rate at which the
noise is occurring. |
• | Compare the engine sounds to other engines and make sure you are
not trying to correct a normal condition. |
|
Noise on Start-Up but Only Lasts a Few Seconds
|
• | Improper oil viscosity. Install the recommended oil viscosity
for the expected temperatures. |
• | Incorrect oil filter without the anti-drainback feature |
• | Worn or dirty valve lifters |
• | Excessive piston to bore clearance |
• | Excessive piston pin to piston clearance |
• | Excessive crankshaft bearing clearance |
|
Knocks Cold and Continues for 1 to 2 Minutes
|
• | Loose or broken crankshaft balancer or accessory drive components |
• | Excessive piston to bore clearance |
| A cold piston knock which disappears in 1.5 minutes should be considered
acceptable. |
• | A cold engine knock usually disappears when the specific cylinders
secondary ignition circuit is grounded out. |
|
Intermittent Noise on Idle, Disappearing When Engine Speed is Increased
|
• | Improper oil viscosity. Install the recommended oil viscosity
for the expected temperatures. |
• | Lower than specified oil pressure |
| Install an oil pressure gauge and measure the engine oil pressure. |
• | Dirty or worn valve lifter |
|
Valve Train Noise (Rattle/Tapping)
| The following conditions may cause
a valve train type noise:
• | Lower than specified oil pressure |
• | Worn or faulty oil pump |
• | Loose oil pump-to-engine block bolts |
• | Loose valve rocker arm attachments |
• | Worn valve rocker arm bearings |
• | Worn valve rocker arm and/or pushrod |
• | Worn, dirty, or faulty valve lifters |
• | Worn camshaft lifter lobes |
• | Worn valve guides or valve stems |
• | Bent, broken, or damaged timing chain sprocket teeth |
• | Evaporative emission (EVAP) purge solenoid or damaged or missing
isolator |
|
Knocks at Idle Hot (Rumble/Knocking)
| The following conditions may cause
a knocking noise:
• | Malfunctioning accessory drive system components |
• | Loose or broken crankshaft balancer |
• | Detonation or spark knock |
| Check for proper operation of the cooling, knock, and ignition control
components. |
• | Excessive connecting rod bearing clearance |
• | Excessive piston pin to bore clearance |
• | Excessive crankshaft main or thrust bearing clearance |
• | Loose torque converter bolts |
• | Cracked or damaged flywheel |
• | Exhaust leak at the manifold |
|
Exhaust System Noise and/or Leakage
| Exhaust system noise and/or leakage
may be caused by the following conditions:
• | Improperly installed or misaligned exhaust system components |
• | A cracked or broken exhaust manifold |
• | Damaged or worn gaskets and/or seals |
• | Burned or rusted out exhaust system components |
• | A broken or loose exhaust clamp and/or bracket |
• | Loose, damaged, or deteriorate Air Injection Reaction (AIR) components
(if applicable) |
|