GM Service Manual Online
For 1990-2009 cars only

Symptom

Cause

There are four steps to diagnosing engine noise. You must determine the following:

    • The type of noise
        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
    • Broken valve spring
    • Sticking valves
    • 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
    • Bent connecting rod
    • 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)