valve chatter

[Gettin-Higher]

89 YJ 4 banger 151k miles.. all of a sudden yesterday, I start getting a lot of valve chatter under acceleration. If I'm maintaining speed it goes away. If I accelerate slowly (and I mean reeeeaaaallly slow) it won't do it. I have 92 octane in it and have run half a tank with no problems. I do have a new fuel filter to put on it since I just got the jeep and have no idea when it was changed last. The previous owner did say they changed the oil about 50 miles before I bought it, but when I checked (and consequently drained) it, it was overfilled by almost a full quart. (They also had put slick50 in it for the first time). Any ideas what could be causing this?

[DanB98TJ]

Not quite sure I understand, but did running the 92 octane get rid of the problem? If so, you're likely experiencing "pinging" (also known as spark knock or pre-detonation). Higher octane fuel will normally lessen or eliminate it.

A few things to check are:

*Ignition timing (not sure if it is adjustable on yours - if you're carburated it should be).
*Replace the spark plugs. It is possible that ones with the wrong heat range were installed and could lead to pinging.

Pinging can also be caused by carbon build-up in the combustion chambers. Some carb/injector cleaners claim that they clean carbon deposits, but I'm not sure how effective they are.

If the pinging only happens during light accelleration and isn't excessive, I wouldn't worry about it. However, if it's like mine and does it during light accelleration, heavy accelleration, and cruise, it may eventually cause damage to the engine - like burning a hole in the piston.:eek:

As far as the Slick 50, I don't think it could cause the pinging, but I have never used it.

[Gettin-Higher]

well there goes my credibilty on engine noises. Turns out it's a minor exhaust leak, just can't pin point it yet..

[Gettin-Higher]

Woo-Hoo.. that was my 30th post to make me a member!!

[DanB98TJ]

Originally posted by Gettin-Higher
[B Turns out it's a minor exhaust leak, just can't pin point it yet..

Look closely on the exhaust manifold for a black, sooty build-up, espeically around the gasket areas or where the pipes join. Hopefully it's just a bad gasket and not a cracked manifold.:(

[Gettin-Higher]

Well, finding this thing is a pain in the arse. I'm hoping not to have to remove the intake manifold just to get the heat shield off. But if it is cracked, I guess there's no better time to put a header on it..