Low compression sanity check

[Schlum1]

I've been reading a lot on this forum as I picked up an 06 unlimited about a month ago and have had a sort out a few things (thanks to everyone who posts such helpful info). I've put 240 miles on it trouble free, until last week. Drove to work just fine, but when I left it started with a very rough idle. By the time I got home I had a CEL for cylinder 1 misfire. I have since changed the plugs, coils, IAC, and O2 sensors with OEM parts to no avail. Still idled rough cold or hot, and didn't get better with rpms. I pulled the plugs again and found #1 was brown like oil soaked, so I did a compression test and it was only 100#, the others were fine in the 150# range. Oil and coolant appear OK. I'd hate to spend the cash on a reman if it were something simple like a head gasket or even just a bad valve. PO said it got a 'new' engine at 120k, it now has 190k.

Long and short, runs rough due to low compression on cylinder 1. Anything else I can verify or check before it starts getting expensive? I can't believe it would be ring or valve related since it went from fine to not fine just sitting for a few hours. Thanks for the help.

 

[Gilaguy23]

That sucks. Stuck lifter possibly and at this point what left to try besides a does of MMO in the oil pan. Im not a believer in such remedies but I did see it first hand on a spent 350 with sticking valves.

 

[macleanflood]

Pull the valve/rocket cover and see if you have a stuck valve.

-Mac

 

[Moglocker]

Pull the valve/rocket cover and see if you have a stuck valve.

-Mac

My 2002 had the same problem,it would fix itself and then months later rotate around and get tight in the guide.had to finally install a rebuild tupy head(wasn’t about to spend a dime on the old non tupy)all is good now.mine was a po301 and when I took the springs off I could spin all the valves by hand except that one.

 

[Gilaguy23]

Err...Valve is what I meant.

 

[Schlum1]

Appreciate the helpful thoughts. Valves looked fine so had a friend used his bore scope and cylinder 1 is full of racing stripes... so needless to say ill be replacing the motor. Often times it's something simple like a sensor, other times, not so much.

 

[jeepguy03]

Ugh that sucks. Sounds to me like they threw in a used engine or rebuilt engine they may not have thoroughly checked. Not sure what your plans are going forward with this Jeep, but if it were mine I'd just find a low-mile good used engine and have it swapped by someone who can verify the condition of it prior to putting it in. Rebuilt engines seem all over the map these days quality-wise, so that might not be the easiest route, even with a warranty. I trust a good used factory built 4.0L over one that was thrown together with cheap parts and spray painted.