The clearance problem area is located by inserting a feeler gauge between each lifter and valve, or between each rocker arm and valve tip, until the noise subsides. Tappet noise can be caused by improper valve adjustment, worn or damaged parts, dirty hydraulic lifters, or lack of lubrication. To correct the noise, adjust the valves, replace any worn or damaged parts, or clean or replace the lifters. Preignition and detonation noises are caused by abnormal engine combustion. For instance, detonation knock or ping is a noise most noticeable during acceleration with the. engine under load and running at normal temperature.
Excessive detonation can be very harmful to the engine.
It is often caused by advanced ignition timing or substantial carbon buildup in the combustion chambers that increases combustion pressure. Another possible cause is fuel whose octane is too low. Detonation knock can usually be cured by removing carbon deposits from the combustion chambers with a rotary wire brush as well as recommending the use of a higher octane gasoline. A malfunctioning EGR valve can also cause detonation and even rod knock. Sometimes abnormal combustion combines with other engine parts to cause noise.