1991 Jeep Cherokee Problem

RELLIKNIKCUF

MEMBER
1991 JEEP CHEROKEE

I have a 1991 Jeep Cherokee 4.0 L automatic. Sometimes it runs and shifts fine, most of the time it doesn't. I get error codes for Oxygen Sensor Signal Lean and Alternator Field Switching Improperly. When I first start it up, it idles at 1500 RPM and gradually increase to 2300 RPM. I shut it off and it won't restart. The exhaust smells like straight gas fumes. When I finally get it to restart, it idles at 1300 RPM and drops down to 1000 RPM and back again. About every 4th or 5th cycle of this, it drops down to 500 RPM or less and almost dies with black smoke coming out of the tail pipe. On the road, it won't shift by itself unless I get the engine up to 4000 RPM - 4500 RPM. I can get it to shift at a lower RPM by getting it up to 2800 RPM - 3200 RPM and taking my foot off the gas. Sometimes that doesn't even work and I cruise around town at 30 MPH and 3500 RPM with everyone staring at me. The problem will go away for a few days and come right back, sometimes in the middle of driving it, it will downshift and I have to play footsie with the gas pedal again. I have a feeling it is sensor related, but I don't have much money and don't want to waste it changing parts that don't need to be changed. Any help or advise would be greatly appreciated.

edit: I changed the MAP sensor and nothing changed. Could it be the oxygen sensor? The fact that it has started working fine all by itself a few times makes me think that it is not a vacuum leak.

2 Replies

RELLIKNIKCUF

MEMBER
53 POSTS

Can this be a vacuum leak? The difference between normal and bad are extreme. I mean it has been running and shifting fine for the past month, then I started it up and the idle immediattely dropped down and then back up and stayed normal. But when I pulled out of the driveway, it shifted like I had it to the accelerator to the floor but I was driving normal. Crusing around town at 30 MPH in first gear is not fun. So what is my problem? I got a MAP sensor code the day before I started having problems, but I changed it out before and it didn't fix it. It has plenty of power and is idling mostly normal. PLEASE HELP! Thanks.

Oh, my heater also stopped working. I was able to beat on the black box under the glove box and it would start working. Then it would run real slow even on high. Now it won't come on at all. Any ideas?

Also, I drove my Jeep back to work from lunch today and instead of babying it like I usually do when it is running like this, I drove it hard and let it shift on it's own at 4000 - 4700 RPMs. By the time I got back to work, (about 5 miles), it was shifting fine on it's own at around 2200 RPMs. I would really like to know what is going on.