A light tapping noise at one-half engine speed, or any varying frequency, may indicate a valve train problem. These tapping noises will typically increase with engine speed.
Before attempting to diagnose valve train noise, check for correct oil level and thoroughly warm up the engine. By doing this you will bring all engine components to a normal state of expansion.
While sitting in the drivers seat, run the engine at various speeds and listen for any abnormal engine noise.
When diagnosing a valve lifter noise, always use a listening device such as a stethoscope. Tools such as this will help to isolate any lifter noise and identify noises that could be mis-diagnosed as lifter noise.
Checks
| Action
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Light tapping noise similar to valve train noise
| This light type of noise may be caused by the following:
| • | Evaporative emission (EVAP) purge solenoid |
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Causes of valve train noise
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| • | Any or a combination of the following can cause valve train noise. |
| - | Loose valve rocker arm attachments causing excessive valve lash |
| - | Worn or damaged valve rocker arm bearings |
| - | Worn valve rocker arm and/or pushrod |
| - | Worn, dirty, or faulty hydraulic valve lifters |
| - | Broken hydraulic valve lifters guide |
| - | Worn valve guides or valve stems |
| - | Worn, damaged, or missing collets |
| - | Excessive play in the camshaft timing chain |
| - | Bent, broken, or damaged timing sprocket teeth |
| • | Low engine oil pressure caused by the following: |
| - | Poor oil quality caused by water contamination, aeration, or fuel dilution or incorrect oil viscosity |
| - | Worn or faulty oil pump |
| - | A loose oil pump pick-up tube |
| - | Blocked oil pump pick-up screen |
| - | Loose or damaged oil transfer tube |
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