My 88 was doing the same thing when i bought it. i built it as only a trail truck so it doesnt have to do it everyday. Just take and drop the oil pan and check a few rod bearings , it only takes a few minutes(easier if lifted)
If they look bad and all brassy thats the problem. See what they are if they are standards just put a new set in it and plastigugae them as you go. If you havent worn the crank to bad that may buy you alot of time before a rebuild. .003 will be allowable but alot and shouldnt knock. i did mine and i am from .003 up to .006 I still have some knock at startup but owell its a $300 jeep. Maybe you caught it early enough to get by with that.

 

well, this jeep is long gone, but the knocking was found to be two rocker arms that had come off and the lifters were just in there having fun in their bores...

 

HOLY 2 year bump...but an update nonetheless. Did you get another one (jeep), or something else?

 

We just got another XJ, a white 91 Sport. I will snap a few pics tomorrow and start a (slow) build thread on it. I say slow because I am also building a 77 DJ5 postal jeep and most of the XJ mods will have to be slipped under my wife's radar since it is her DD

 

Sound radios funny. I'd go ahead and pull the little inspection plate off the bottom-front of the bell-housing and check the torque converter to torque plate bolts. Good to do anyway, since it seems to be pretty common they loosen. Mine were funky.

Well, check spark and see it it fires with starting fluid. You should hear the fuel pump for about two seconds when you first turn on the key. (Is does crank?) Power to the pump goes out the rear of that ceramic ballast resistor there by the air cleaner. That you can safely bypass. Anyway power needs to get through there for the pump to work. Also on the fuel rail there is a schrader valve, like a tire valve. You can depress that and see that it shoots fuel into the rag you are holding there.

You might also inspect your crank pulley, (it's two piece with a rubber deal), and see it's bolt it tight. (3/4-19mm I think). They can knock.

So there's that!

In my signature is Cruisers "mostly Renix". There is a deal there on cleaning the ICU to coil contacts. It's pretty common ANY problem is a wire or connection.

OH! (Haha). I just "got on the page! Well, info is info!