compression test results and spark plug condition questions

I was curious what the compression was on my 92 xj 4.0 5 speed with 174,000 miles,so I did a compression test today. the 1st 3 cylinders were 140-145 psi. cylinders 4 and 5 jumped all the way up to 160,and cylinder 6 was back down to 145. is this ok,or should I be worried about the 2 cylinders that were higher than the others? also,the plugs had a tan/white residue on them. Is this normal? I didn't replace the plugs,they were new about 6,000 miles ago. I just cleaned them off,checked the gap and re-installed them. thanks,Ben

Not real sure about the compression #'s, but they sound good. I would be concerned if you had 1 or 2 cylinders at 60 lbs, but you sound like you're OK there. As far as the plugs, that's what you want to see. Tan is good, white is lean. It sounds like you're in the middle, so :thumbup:

Compression's healthy in all six cylinders and plugs are good. That 174k mile old puppy's got a lot of life left in it yet.