I recently did a compression test on my 98 xjr due to my misfire code on cylinder 4. Come to find out it’s has low compression in on cylinder out of all of the others.

The compression was 75psi what do I do to fix this problem on a budget avoiding buying a new engine?

 

Wet or dry compression test?

A little bit of oil down the plug hole & then compression testing is a wet test. If that restores the compression to near normal I'd suggest it's rings/bore at fault. If it makes no difference it's head gasket or valves.

 

Low compression in one cylinder is not necessarily a huge problem.
That is, of course, assuming there are no nagging issues as a result.
I have seen X308s drive for years with that condition.

 

Lead us up to when it started to misfire. Where you just driving gently along and it started to miss? How many miles are on the car?

 

Any warning lights? Codes?
It sounds like a faulty coilpack, like sparkplugs they wear out. My course of action would be:
remove the fuel pump relays and put a drop of oil in the low cylinder, then turn over to get oil around and pressure up.
re-test. Get hold of a replacement coilpack.

 

On other cars, I have seen faulty individual coils cause all kinds of problems.
Fortunately in most cars, you get some warning by a trouble code which defines
the cylinder that is misbehaving. Now, if it's a burnt valve causing the low compression,
that is something else.

 

I did actually poor some oil in that number four cylinder which had low compression and it did bring up the compression to the recommended rating. The car has just over 100,000 miles on it.

should I try rislone ring repair additive to see if that fixes the issue.

i’m also thinking maybe the car has a broken or stuck piston ring how would I determine which one it is