Join Date: Jul 2002
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Name that engine noise...Please help!
Didnít really find an answer doing a search, so here it goesÖ
I have a 1990 YJ with the carter carbed 258 motor and 5 speed trans. Motor has 115k miles on it. Lately, itís been making an awful racket. The noise is NOT present at normal idle speeds hot or cold. Noise presents itself when the motor is revved above 1500 rpms whether in neutral or in gear; whether coasting or accelerating. Iíve run the engine removing one spark plug wire at a time and it made no difference. Noise remained. Iíve removed the fan, and the fan belts from the alternator and power steering pump and again, the noise remains. I recently replaced the distributor, timing chain, and water pump. I previously had the timing chain slap noise (chain hitting the front cover) which is now gone only to be replaced by this new noise (which for all I know could have already been present and I just couldnít hear it over the timing chain slap noise). The best I can describe the noise is a rapid chit-chit-chit, almost like a diesel sound. Like I mentioned earlier, itís not present at engine speeds below 1500 rpms. I canít really pinpoint the area of the motor where itís coming from either. Itís pretty loud though as even some people have commented on hearing it as I passed them by. My oil pressure is good and driveability/performance doesnít seem affected. I doubt itís an exhaust leak as Iíve checked the manifold to front pipe and thereís no apparent leak. I even ran some Marvel Mystery Oil the last oil change interval with no benefit in eliminating the noise.
Anyone have any ideas on what it could be or common ailments with the 258 motor that would produce such a noise? Without pulling the motor apart, how do you know if itís rod knock or piston slap or wrist pin slap, etc. Itís really beginning to drive me crazy not to mention how embarrassing it soundsÖlike Iím driving some hunk-of-junk.