Hammering / knocking noise on 4.0L6 '99 Cherokee

I would say, I have a severe case of piston slap, but from what I have found out about the infamouspiston slap problem, it should have ended long before 1999. So, what problem do I have on my '99 Cherokee? The symptoms are very similar to the legendary piston slap: Symptoms vary from no noise, to a light ticking, to a ticking/hammering to a strong and very audible hammering/knocking noise. The noise is generally more pronounced at start up, when the engine is cold. Sometimes, the noise disappears when the engine warms up. Sometimes, when the noise appears at start up, stopping and immediately restarting the engine stops the noise completely. The symptom is most noticeable during idle, but will get louder as engine speed increases, and sometimes appears / disappears randomly on a warm engine and at various driving conditions. While this noise was very infrequent before, now it is a almost daily occurrence.

The engine has about 60K and was serviced regularly at the local dealer, with oil and Mopar filter changes every 3,000 Miles. The engine runs, starts, and idles otherwise completely fine. No significant oil consumption either.

The dealer here in Thailand suggests to open up the engine, and perhaps change the hydraulic lifter, but he is basically not really sure, what causes the problem.

I have used a Fuel Injector Cleaner without success.

Most likely, it is not the piston slap problem, as the car is built in

1999. If it is the lifter, why stopping and restarting the engine clears the noise immediately sometimes, but not all the time. The noise appears at a cold engine and on a warm engine as well, and during idle but during normal driving conditions as well, but randomly, it seems. If drive at high rpm, there is generally no noise.

What could cause that noise?

Any help from you old timers and experts would be greatly appreciated.

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Reply to
Robert Goldpalm
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I suspect now more of a electronic problem. Could the cause of this problem be found within the electronic / contact / sensor input complex?

Today, no noise at all, so far. No noise at cold start, no noise during normal driving conditions with a warm engine. No noise whatsoever.

So, if it would be a purely mechanical problem such as piston slap, hydraulic lifters, or carbon build up, why is there no noise today, or why can stopping and restarting the engine sometimes stop the problem immediately?

I am living in the tropics (Thailand) with a very high humidity of around 80-90%. Could it be, that somewhere, an electronic contact or a wrong sensor input causes the engine to produce this ticking / knocking sounds sometimes?

Reply to
Robert Goldpalm

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