compression loss

So, I picked up a 98 XJ, 231k miles on the clock. The thing is clean, but has a compression issue on the #1 cylinder. Has a dead miss, and a compression test showed the following: Cylinder 1-50 psi. Cylinders 2 through 6 all around 150 psi. Dumped a little oil in the #1 cylinder and rechecked, came up to around 100 psi. There can't be a hole in the piston, so I assume it's either rings or a scored wall. Is there anything (Marvel Mystery Oil or the like) that I can dump in there to see if anything changes? I do have a motor out of a 91 that I can throw in if needed, just have to swap over the intake/exhaust. I'd just like to avoid it if at all possible.

With that large of a variance, and the improvement from the oil in the cylinder, I doubt any "new engine in a can" product will help you.

Doesn't mean you can't try them, but with a 2/3 loss of compression??

That's kinda what I've been thinking, just want to see if anyone has tried this with success. I'm not afraid of an engine swap, I've done enough of em, I just want to get the motor issues fixed quick so I can move on to the fun stuff.

With just one low cylinder, have you considered pulling the pan, pulling the rod cap and slipping that piston and rod out of there? Might just hone that one cylinder and re-ring that piston and get another 150K out of that 4.0, might consider a valve job at the same time.

MMO wouldn't be my choice, I'd try that Restore product. Use an 8cyl can's worth.....can't hurt it anymore....but I dunno how long it takes for that stuff to "do its job".

Probably better doing what joe said....