I love JB weld, but JB weld is not a good application for a cylinder head crack repair.

Even the guys that have tried actual welding of those cracks have been unsuccessful. You may still have enough of a crack to cause your misfires.

I would get that head off of there.

 

^x2

and 500 rpm is NOT normal. FSM says 750rpm hot idle in D.

 

problem started after plugs and throttle body work was done

 

May want to try some NGK plugs on there as that is a great plug for the 00-01 4.0 and eventually what Jeep used for their OEM plug.

But my advice on getting that head off there still stands. J&B won't work on a cracked cylinder head. It just has nowhere the strength needed to work on that type of hardware fail in such an extreme environment.

And the misfire could still be related to the cylinder head, just became more pronounced after some recent maintenance work.

And when coolant starts mixing with the oil (again?), you're putting your engine bearings at risk, and that misfire may then be the least of the owners concern.

Just not worth it.

 

Take the plugs back and tell them they are bad. They will exchange them. Sounds like it's something you changed not an epoxy on the head. The jb weld is not something you should worry about YET. Jb weld is amazing stuff and don't worry untill you have problems with that. Jb weld has been fixing expensive repairs for years for us cheap folks.

 

I just dont have the money for the head right now, I will be replacing it in a few weeks. That was my intent from the beginning, Im waiting on a tax return. I also have to arrange for a loaner/rental vehicle while I put the new head on.

The oil is good, I keep an eye on it, and like I said I have no coolant loss so it seems to be holding for now.

I just took it out for a drive. It seems to be perfect now, it's idling nice and smooth, I wonder if the computer needed to adjust to the plugs actually firing correctly. It was still slightly rough but after a mile or so it seemed like it righted itself, sitting at stoplights it's nice and smooth. Idle is still below 700 but Im not terribly concerned about that till next weekend.

Any continued thoughts are much appreciated! Thanks guys!

 

500 RPM IS NORMAL on a 2001 Cherokee 4.0 Manual transmission or Auto Transmission with Heater/A-C off, and said Auto in Park or Neutral.