We have a 6cyl 98 jeep, 4.0.
runs bad, compression low. Head replaced with used with all new gaskets.
jeep still runs like crap.
We did a compression test tonite.
1) 25 lbs
2) 27 lbs
3)98 lbs
4)96 lbs
5)50 lbs
6) 52 lbs

WHat gives? why did this motor blow up so perfect?? im new at this game so any insight would help.

 

Oh P.S.
We added oil on a second compression test and the numbers didnt change, well not that we could tell

 

sound like you have poor sealing valves,is there any play in the rockers when its not running?

 

6 months ago I did a sparkplug and oil change on my Jeep. I went with the recommendation of Champion Truck plugs,
I noticed right after installing the plugs that there was no big noticable change in the way the Jeep ran. Now over 6 months I noticed My regular gas milage has dropped from the normal 15 mpg to 12 and 11 on the highway. I regulary clean the air filter and still use the same gas from the same station, and have not changed my driving habits at all. It makes sense that the only thing that has changed is the plugs.
My Question: Has anyone used the E3 Spark Plugs and what are your thoughts on them?
Also What other gas Mileage mods have you all done?

 

Check for a vacumn leak , maybe you hit a hose when doing the plugs . Plastic crap is very brittle . It would explain your poor economy .

 

Piston rings possibly all seized to pistons, and not sealing. Unlikely, but jumped camshaft, one or two teeth out... and causing low compression (check timing according to shop manual). I have seen the latter once, on a 91 but it did not run at all. Being yours is a 98, the timing is set by cam/crankshafts. worst case, pull the front cover (harmonic balancer) and take a peek. If you engine is not coding bad timing, it is possible to have literally ran this engine out of oil a few times?? maybe not changing your oil?? This will cause the rings/pistons to turn into manhole covers... in other words useless.

It is possible, that the machine shop took too much off you head (planing if you had this done). And the valves are leaking by. Another unlikely cenario, because of the hydraulic lifters. But a possibility.