TerraWombat
NAXJA Forum User
- Location
- Eastern Shore MD
If ya just want to skip down to the problems part and not read my awesome story, skip to the third portion of this thread.
Background Story
My uncle's neighbor bought a 1988 Jeep Commanche Pioneer back in '89. Came with the 4.0L Inline six and the four speed automatic transmission. The guy loved the truck and primarily used it as a worktruck. Last year, the thing started giving him a lot of problems and would randomly die out, but would fire right back up if he put it in neutral. He said he couldn't exactly pinpoint when it would stall, sometimes it would be on a very mild acceleration, sometimes around a turn, and sometimes when he came to a stop. He said he took it to his mechanic and they replaced some sensors, but he wasn't sure which, but after that, the truck ran fine, apparentely. Last year, he said he was driving and the thing just quit and would not fire back up at all so he had it towed home under a tree and let it sit there until yesterday.
Where I come In
He called up my uncle and said he was going to take the truck to the scrapyard and junk it...wanted to know if my uncle was interested in the truck. Uncle told him no thanks, but he called me up right after and wanted to know if I wanted it. Hell yea I want it, especially for the price of FREE! So I went and picked the truck up yesterday, got the bill of sale, yadda yadda (guy wrote down like $100.00 for the price....said it was a parts vehicle). I lugged it home, pushed it into my shop, and began the troubleshoot. First place I looked was under the distributor cap, and much to my surprise, the rotor was completely melted! I own another '88 MJ, and I just sold an '86 MJ and a '90 MJ so I've got a few spare parts lying around
I threw in a spare rotor, charged up the battery, cranked the truck over, and it fired right up! Sweet, a free truck that still runs!
The Problems
Now, the truck may run, but it doesn't run well. With the truck in gear, and with light-mild accleration, it wants to stall and die out. I need to go at least 1/2 throttle for the truck to run fine. Once I get past the acceleration and just want to cruise, the truck is fine. Doesn't want to stall or hesitate or buck...it's just the initial acceleration which kills it.
The thing idles great though, responds to changes in engine load at idle too (I.E. turning the steering wheel, turning on the AC, which works!) so I suspect that the IAC stepper is fine.
I checked the TPS sensor for proper operation. It gets 5V from the power source, and at closed throttle, gets 0.76-0.78V. Using a smooth transition from closed throttle to wide open, the volts steadily increase with no flat spots or jumps. I suspect that the TPS is just fine.
With my past experience with these trucks, and these engines, I've already gone ahead and purchased a new crank position sensor. The old one is giving me a reading of about 215 ohms, but the new one is around 200 ohms. I'm not quite sure if the thing is bad or not, but it is covered in a combo of ATF, motor oil, and dirt, so I think a new one wouldn't hurt.
The oxygen sensor gives me a reading of 3450 ohms, which is entirely too high, but I'm to understand this is just checking the heating element inside, so I'm not too sure if this is bad. I also bought a new oxygen sensor just in case, just haven't gotten around to installing it.
Conclusions
If you've gotten this far, thanks for reading. I wanted to make sure I got everything that I've done thus far out on paper, whether I'm headed in the right direction or not. My plan is to replace the CPS and oxygen sensors today to see how the truck responds. I also bought a new muffler and tailpipe for it, although I know that won't change anything other than the noise it emits. the catalytic converter will be coming off too since it needs a new gasket, so i'll check to make sure that it isn't clogged. I will also be replacing the fuel filter since I have a new one lying around. If there's anything I'm missing, let me know. I think I'm on the right track to fixing this thing. Instead of trying to pinpoint what might be wrong, I'm just going to replace everything I know to go bad on these engines. I got the thing for free, might as well put a little money into it
Background Story
My uncle's neighbor bought a 1988 Jeep Commanche Pioneer back in '89. Came with the 4.0L Inline six and the four speed automatic transmission. The guy loved the truck and primarily used it as a worktruck. Last year, the thing started giving him a lot of problems and would randomly die out, but would fire right back up if he put it in neutral. He said he couldn't exactly pinpoint when it would stall, sometimes it would be on a very mild acceleration, sometimes around a turn, and sometimes when he came to a stop. He said he took it to his mechanic and they replaced some sensors, but he wasn't sure which, but after that, the truck ran fine, apparentely. Last year, he said he was driving and the thing just quit and would not fire back up at all so he had it towed home under a tree and let it sit there until yesterday.
Where I come In
He called up my uncle and said he was going to take the truck to the scrapyard and junk it...wanted to know if my uncle was interested in the truck. Uncle told him no thanks, but he called me up right after and wanted to know if I wanted it. Hell yea I want it, especially for the price of FREE! So I went and picked the truck up yesterday, got the bill of sale, yadda yadda (guy wrote down like $100.00 for the price....said it was a parts vehicle). I lugged it home, pushed it into my shop, and began the troubleshoot. First place I looked was under the distributor cap, and much to my surprise, the rotor was completely melted! I own another '88 MJ, and I just sold an '86 MJ and a '90 MJ so I've got a few spare parts lying around
I threw in a spare rotor, charged up the battery, cranked the truck over, and it fired right up! Sweet, a free truck that still runs!The Problems
Now, the truck may run, but it doesn't run well. With the truck in gear, and with light-mild accleration, it wants to stall and die out. I need to go at least 1/2 throttle for the truck to run fine. Once I get past the acceleration and just want to cruise, the truck is fine. Doesn't want to stall or hesitate or buck...it's just the initial acceleration which kills it.
The thing idles great though, responds to changes in engine load at idle too (I.E. turning the steering wheel, turning on the AC, which works!) so I suspect that the IAC stepper is fine.
I checked the TPS sensor for proper operation. It gets 5V from the power source, and at closed throttle, gets 0.76-0.78V. Using a smooth transition from closed throttle to wide open, the volts steadily increase with no flat spots or jumps. I suspect that the TPS is just fine.
With my past experience with these trucks, and these engines, I've already gone ahead and purchased a new crank position sensor. The old one is giving me a reading of about 215 ohms, but the new one is around 200 ohms. I'm not quite sure if the thing is bad or not, but it is covered in a combo of ATF, motor oil, and dirt, so I think a new one wouldn't hurt.
The oxygen sensor gives me a reading of 3450 ohms, which is entirely too high, but I'm to understand this is just checking the heating element inside, so I'm not too sure if this is bad. I also bought a new oxygen sensor just in case, just haven't gotten around to installing it.
Conclusions
If you've gotten this far, thanks for reading. I wanted to make sure I got everything that I've done thus far out on paper, whether I'm headed in the right direction or not. My plan is to replace the CPS and oxygen sensors today to see how the truck responds. I also bought a new muffler and tailpipe for it, although I know that won't change anything other than the noise it emits. the catalytic converter will be coming off too since it needs a new gasket, so i'll check to make sure that it isn't clogged. I will also be replacing the fuel filter since I have a new one lying around. If there's anything I'm missing, let me know. I think I'm on the right track to fixing this thing. Instead of trying to pinpoint what might be wrong, I'm just going to replace everything I know to go bad on these engines. I got the thing for free, might as well put a little money into it
