jeephack

No overheating or exhaust fumes. Was running fine. Started noticing coolant loss and gain in crankcase volume. I have a HO head that I've been wanting to try. Guess now would be a good time!

Think I may have a head gasket problem. Any opinions??

Renix era temp sensor was single wire, single terminal .

Thanks. I'll look into these possibilities. Funny thing is, it was running fine but it sat up for a month or so without being started. When it was started again, the miss/backfire was there.

Cove City. Know you've passed by the exit many times on 70.

Thanks onlyinajeep, I'll have to try this "IF" I can get it to idle long enough. Thing is running so ragged that it cuts off if I try to let it idle.

Recently, one of my Comanches has developed a severe backfiring problem. Almost to the point of being undriveable. 1987 4.0 Fuel pressure is correct. Spark is consistent. New plugs. Problem is so bad that I even went through the procedure to make sure the distributor was installed correctly. I started it today and held it at high rpm for a couple of minutes. Backfired the whole time. Afterwards, I noticed that the catalytic converter was extremely hot and smoking. Smelled terrible also. My question is, can a clogged catalytic converter cause this kind of backfiring and terrible idling?

Actually I don't have one. I have an air powered version. I have those too. Straight and right angle. I just use the Dremels for tight spots.

cruiser...you mean there are people that don't have Dremel's??? onlyinajeep.... Ever heard of Cove City? Halfway between New Bern and Kinston on US 70. About 45 minutes from the ocean.

I have a '87 MJ with the 4.0 . Recently, I have been losing coolant and gaining in crankcase volume. Guess I'm looking at replacing a head gasket. I also have a 4.0, HO head residing in my garage. Would there be any advantage to be gained by swapping the in the HO head?

I have an '87 MJ, 4.0 5 speed. I also have a '90 parts XJ, 4.0 auto sitting in the weeds. If I swap the XJ ECU into the MJ, I could possibly get a little better performance? Great!!!

I recently purchased a '97 ZJ for $250. The PO had been having problems wiith the "fuses & relays" in the fuse block behind the battery and could never get it figured out. I brought it home and replaced both battery cable ends and now I have a really good clean Jeep for $250!

I have had a dash wire harness become dislodged and fall across the throttle cable keeping it from retracting completely. Probably not your problem but it only takes a few seconds to check.

I went with Kobalt. At least if I bust it, I can get a replacement.

That's all solid. The leak is almost directly behind the head where it can't easily be accessed. Got a new socket, so I'll know before long!

At first I thought head gasket,but after further consideration, I'm leaning towards freeze plug. Either way, the head comes off. And Jim, I was 16 years old when I bought the socket. I thought I was buying a quality tool. (Western Auto) That was 45 years ago. I guess nothing lasts forever. :)

I have a 4.0 that when reaching operating temperature, starts blowing steam/coolant out the back side of the head. Can't see exactly where it is leaking from. The engine runs smooth and the oil is clear. I.E no coolant. Is this more likely to be a bad head gasket, bad freeze/expansion plug, or cracked head? I'm in the process of pulling the head but I busted my last proper size socket and haven't purchased another one yet. Just wondering what the consensus is from the learned minds of this forum?

I had a problem with a very high idle a couple of years back. Jeep would start and idle at around 3000/3500 rpm. After going through all the aforementioned procedures to no avail, upon closer inspection I found that one of the wiring harnesses had come dislodged in the dash and fallen across the throttle cable next to the firewall preventing the cable from retracting fully. A quick repositioning and securing of said harness remedied the high idle. Probably not your problem but I know firsthand that it can happen. Only takes a minute to check.

I had a problem similar to this some years back. Jeep idled at 2500-3000 rpm every time it was started and would go no lower. After much dead end testing, I discovered that a section of the wiring harness under the dash had come loose and fallen across the accelerator cable next to the firewall, not letting it fully retract. This is probably not your problem, but it can happen and only takes a couple of seconds to check

Recently, I have noticed that the amount of fluid in the crankcase has been increasing instead of decreasing and the oil seems to be a lot thinner. Oh! and also, coolant is mysteriously disappearing. Any thoughts? :shake:

Glad to hear that everything is working now. Gotta love it when problems turn out to be simple!

That's the one!

It's located on the back side of the lower part of the dash board on the passenger side. It's a little square box with a harness plugged into one side. (or not) :doh:

I had a problem similar to this some time back in one of my XJ's. Come to find out that I had inadvertently unplugged the transmission control module. Once that was plugged back up, everything was fine.

After some consideration, I decided to replace the fuel filter. The truck ran much better. Thought I may have found the problem. After a short hunting trip last Saturday, after I returned home and cut the truck off, it wouldn't start. I tried to start it every evening after work to no no avail. This afternoon, having a little more time to tinker on it, I found that it was not firing. On a whim, I unplugged and cleaned the cps connector. Truck started and ran fine. Might be on to something here.