Lars_XJ99

Hey Guys!
I am new here and looking for some advice. Just moved to Salt Lake City from Germany for research studies and bought myself a 1999 XJ 4.0L with automatic transmission.
Dont know too much about cars but I am learning pretty fast, also thanks to this forum and youtube
My main problem with the car right now is that its lacking a lot of power. I will try to remember everything that happend since I bought the car so this post might be a little longer but I wanna give all the information there is.

When I bought the car it had a rough low idle and the guy who sold it told me that it is probably due to a bad O2 sensor or vacuum leak. First test drive felt good but didnt test the engine under full load (which was a big mistake I guess). I changed the oil and also started changing the transmission fluid aswell. When I took it for a little roadtrip my troubles started. Driving through the city feels pretty normal with the car but going on the highway it has a lot of trouble getting up to 65 mph, barely accelerating and feeling powerless. Going up a long steep hill was even more difficult just reaching about 30 mph with full throttle. RPMs stayed around 2k (throttle open ca 80%). When I pushed the throttle down all the way, it kicked down and RPM went up to 4k and it accelerated a little bit but then shifting down again back to 2k RPM and no acceleration. There wasnt a place to pull over on that road so I creeped up the hill and the car started to overheat aswell. Was able to stop the car shortley after the temperatures went up (ca 3min). I heard noise from under the hood...the coolant in the overflow tank was boiling. After the car cooled down I carefully drove the car home without overheating it again. All that time the CEL was NOT on. Only the check gauges light came on shortly because of the overheating. And I also noticed that the car used a lot of fuel (I would say the MPG was probably below 10).

I read through alot of threads and found multiple possible reasons..TPS, clogged cat, bad fuel pressure seemed to be likely...
First thing I checked was the fuel pressure and that turned out to be normal.
I checked the throttle body and the IAC. Both looked super clean but I found that the gasket of the IAC mount was broken (not the O-ring but the gasket where the whole thing is mounted to the throttle body). A couple of days later (I didnt drive the car much only really short trips like groceries..) the CEL came on. Also noticed the coolant lvl is lower than before so probably the head gasket broke aswell or was broken already broken before everything. I took the car to a shop...

They checked the cat --> looked good
They told me the car has a "rich code" and also "random misfires on all cylinders". Also the upstream o2 sensor was bad and oil pressure sending unit aswell (the oil pressure gauge was stuck at max from the beginning). They checked the grounds which were good and he told me that the spark plugs looked good aswell (which is weird because I later find out they were all black). I let them replace the O2 sensor and that cleared the rich code but not the misfires. They told me the lack of power comes from the misfires and they would do a compression test to see if the head gasket is broken. I got a call with bad news...that the first cylinder has no compression at all (around 15psi) and that it is probably best to replace the engine. The spark plug was pitch black aswell (from running rich I guess?). I asked them about the other cylinders and they told me that they didnt bother doing those because the engine would need replacement anyway. They put in the old O2 sensor and didnt charge me anything because they couldnt fix the car (just had to pay for the diagnostics part). Got my car back (CEL still on) and the shop is calling some yards to look for a used replacement engine to give me a quote on that.
I had the feeling they didnt put too much time in diagnosting the car and just to be sure I did a compression test myself today. Couldnt complete it because my battery got pretty low.
Cold engine and dry test:
#1 90 psi
#2 100 psi
#3 105 psi
#4 105 psi
#5 ? couldnt finish the test
#6 ?
Well I know the compression should be 120-150 psi, so my results are pretty low. Also when the enigne cranked over for the first time I only got around 15-30 psi on all the cylinders I tested. After turning it over around 8-10 times it got to a steady reading. That indicates bad valves on all the cylinders and maybe broken headgasket at #1? Also I did a wet test on #1 which got up to 105 psi (so rings aswell?). Unfortunately my battery was nearly dying and I want to take it to a shop tomorrow and dont have a charger right now. So after reinstalling the plugs (all of them were black) I made a short testdrive around the block. Car was running a little bit better but still no power uphill and the CEL was off which got me confused (did I clear the codes by disconnecting the distributor and pulling fuel pump fuse for the test?).

So the lack of power most likely comes from the bad misfires, right? Why was the CEL not on before?
Running rich comes from the bad upstream o2 sensor + bad compression?
I am also pretty sure that the head gasket is broken because of the compression test and I it is consuming coolant.
Is the engine completely done with these low compression numbers? or could I get away with replacing the head + gasket? --> gonna have to pull the head anyway I guess
Cant do the leakdown test myself because I dont have access to compressed air. Really limited on tools aswell atm :/
I wont keep the car for a long time since I most likely will leave in 9 months again and try to sell it then.
Will go to a few shops tomorrow and ask around for opinions aswell as quotes. Also I will call the shop again to get all the code #s they were reading.

Would be nice to get a few more opinions on that car (really like the cherokee but dont know if this one is worth keeping)
I am thankful for any help and will keep you updated =)

Morat

Woah, that's quite a list.
It sounds like that Jeep has been badly beaten and neglected.
What is the rest of the Jeep like? Is there rust? How many miles are on it?

Ultimately you could throw an oil pressure sensor on it, with new plugs and maybe a headgasket and then retest it all, but that might just be wasted money if those compression numbers turn out to be right you're looking at rebuilding the bottom end at least