When I start my 96 XJ, I hear this bad knock coming from it, granted its cold out, but as the engine warms up, the knock seems to get fainter and fainter, and i don't even hear it while driving, is this normal? Oil was just changed two days ago, i've tuned it, all except D cap and rotor.

 

Could be "piston slap". As they warm up they fit the barrels better. A rod bearing might rap hard a second cold then quiet down, but will persist or worsen as it warms. Just on GP you might want to check the torque converter bolts. They are known to loosen on the 4.0 and cause knocking, but not as you describe. Very easy once you have it up and the little dust cover removed from the front of the bell-housing.
Sooo, be real nice to it while it's cold, nice & easy, keep the RPM's down.

Somebody is probably going to ask you what kind of oil filter you have in a few hrs btw.

 

Good advice ^^and I would assume it's piston slap. The factory fought that for years.

If it's an automatic, I would check the torque converter to flexplate bolts now just cuz they'll probably need it sooner or later.

Gotta ask: What brand of oil filter are you usning?

 

Crap! Cruiser beat me to it!

 

I'm in Arizona and I got up before you?

 

Nope, went to church with the family for christmas this morning.

 

We went last night.

 

Somehow we always end up posting on the same threads... haha

 

Haven't figured it out yet, all I know is, its not present on warm days,

 

Fram?

 

Probably piston slap then.

What brand of oil filter are you using?