Lately I've had a knocking in the 4.0 in my `97 TJ. I cant tell for sure if its coming from the bottom or the top, and it sounds like a diesel at idle when cold. The noise lessens when its warmed up, but is still present. Granted most of my driving is around town, stop and go type stuff, but I've kept the oil changed every 3k and dont abuse it (often).

There has been no performance loss at all, no overheating, no loss of oil pressure. I went back to stock ECU programming last night, even though its never had a tank of anything less than 93octane since I bought it, but the noise persists. I checked for trouble codes when I did the programming, but there were none. I also changed the oil last night (about 800mi late <img src="/forums/images/graemlins/scared.gif" alt="" /> ), going to 10w40 instead of 10w30, hoping the thicker viscosity in the high temp range might quiet it down, but that did not help.

Am I being paranoid? Maybe its the "normal" valve train clatter from the 4.2/4.0 and its only bothering me because I've been listening to it so intently for the past couple weeks? I'm pretty sure one or more of the injectors is not performing optimally (leaky seals, and one or two are "ticking" louder than normal), could that contribute?

Your thoughts?

I'm going to go start it again and see if I can narrow down where its coming from.