I am reposting this because I had originally tacked my problem onto someone elses'.

I have a 91 XJ that has a number of problems. It is really clean though. I bought it for 400 bucks off craigslist and have driven it to work for 6 months. It ran rough when I bought it. it has 297,000 miles on it with original engine. I know I need a new engine soon but I'm building one that won't be done for a while. Did a compression test and 5 cylinders ~ 90-100 psi 1 dead cylinder. Could this be a Head Gasket or maybe a busted valve spring? Just need it to run good while I build another engine. I've done the HG's on a V8 Tbird before (real pain!) so this shouldn't be hard and I found a rebuilt head for $150 on craigslist if need be. It doesn't burn or leak oil.

 

If it is the head gasket you would see coolant in the oil(oil would look milky) and oil in the coolant. if it is a valve issue, you will have to replace the head gasket either way. I would suggest taking the valve cover off and then hand turning the engine to see if all the valves are moving or if one is sticking or something. could also be that one of the valves has alot of carbon build up and is causing a lack of cylinder pressure

 

Head is cracked over the dead cylinder. Probably around the valve seat area.

 

I went ahead and just picked up a head. Gonna replace it weekend after next. Anyone got an ETA on how long it will take? There are gonna be 2 of us doing it. I have a 2 year mechanics degree but its been 8 years since I've done any major engine work. Gonna grab a Haynes and label everything and take pics. I'm hoping to get it knocked out over a weekend. Also gonna replace my Cat. Any ideas on a good cheap cat? I failed emissions, High NO and 10x the O2 limit here in Colorado.

 

So we replaced the head this weekend. Took about a day and a half. Turns out the issue was a broken valve spring. It runs really well now with the new head, however, my temp gauge is dead. Thermostat seems to work, the engine gets warm, heater works, the electric fan kicks on like it should but my temp guage is pegged at nothing. The sensor is conected on the thermostat housing. We did lose a peice of a vacum hose and kind of rigged one, this hose goes into the fire wall. Could this be the issue?

 

Found the issue. The little wire that goes on top of the sending unit in the back was not on well. Checked it after I read some more forums. Temp gauge works now but engine is running a bit hot. Gonna flush the cooling system and get a new thermostat. Probably just running hot because we replaced some of the coolant with water. Not great in CO but it works temporarily.

 

glad to see you got your problems solved. now if only I could fix mine

 

Do a leak down test before you say it's the head gasket or anything. it could just be something simple like a bad injector or spark plug

 

Out of curiosity, which cylinder was gone? I had the same problem on my 96 and it was the #1 intake spring.

 

It was the #6 Exhaust valve spring.

 

Wasn't it good? You must have been getting good mileage with 5 cylinders?

 

The mileage sucked with the dead valve. However since I replaced the head and fixed the coolant system I am saving about $10-15 a week in gas. My compression also went back up to good levels in all cylinders. About to roll over 300,000 miles and with the new head I bet my engine makes it to ~500,000. When I pulled the head wall measurements were still good, no scoring, pistons looked great and rings seemed to look well seated and in good shape. As long as the bottom end holds up these straight 6's are beasts when well cared for. Now if I could only fix the death wobble....