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96 XJ 4.0 LOW COMPRESSION QUESTION

krwalkman

NAXJA Forum User
Location
Thornton, CO
Hey all, I need to give a little bit of back story.

1996 Jeep Cherokee 4.0, 197k miles. Pretty well modified for wheeling, no motor modifications other than 4 hole injectors.

Early last year I bought a sport instrument cluster so I could have real gauges instead of dummy gauges. I then purchased the temp sensor needed to make the temp gauge work and decided to change it right before a trip (I always put off jeep work until the day or so before a trip...lol).

So I went to remove the OEM temp sensor on the rear of the motor and it snapped off at the threads. Since I was leaving the next day I didn't have time to get it out. I plugged in the new sensor and just stuck it in the area so it would have some sort of reading. After about an hour drive into our trip the jeep started to overheat. Seems like the thermostat was not opening with inconsistent readings from the sensor. Anyways, we were committed, let it cool off and it didn't happen again after we fixed the sensor in place with some creative zip ties.

Jump to a few weeks later, I got the broken threads out of the motor and started to install the new temp sensor. The non-dummy sensor has the bolt head lower down and it would only so far until the valve cover was in the way and it wouldn't tighten any further. I tried every tool I could think of to try and get it down further with no luck. It seemed to be into the thread sealant already so I figured it was alright. So then I just leave it, the gauge is working weel. About a week later I started to get a check engine light. Pulled the code and it says low compression. That's it.

So then I dove into compression testing. I read 100-108 dry on all cylinders. I did not block the throttle body open so I imagine that was a little low. Nothing out of the ordinary in my opinion.

This brings me to my question. If the Temp Sensor is not seated all the way could it cause a low compression light by leaking? I have not checked for a leak, but I am unsure that even could be the problem.

Looking for any guidance on the subject. Thanks in advance.
 
I should mention this all happened within 2 weeks. I do not daily drive it, so the timing of things is a little skewed. From over heating to where we are now was probably 1000 miles total.

Fiance just reminded me it overheated on her on that trip a second time when we were wheeling. We have two jeeps so we swap them around sometimes on trips.
 
There really isn't any relationship between the two and that is slow compression even with the TV closed.
 
There really isn't any relationship between the two and that is slow compression even with the TV closed.

I just wasn't sure since it goes into the head if it could leak pressure out and yield low compression.

Yeah, it is low for sure, I just really want it to not be a rebuild haha. It isn't losing coolant or anything at all. Maybe the chain stretched with the heat and timing is off or something, it runs a little rough, but still very driveable realistically.
 
I actually wasn't sure it was low, but I assumed I'd pick up another 10 or so PSI with the TB open, maybe not. After just reading about compression tests I may have performed mine in error anyways. I had all spark plugs in still except the one that was being tested.
 
What is the code number it gives you? I've never had a reader give a code for low compression, and I've had one with 10 psi in a cylinder.
 
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