I have an 89 Jeep Comanche 4.0 L manual fuel injected, lot's of miles 350K +. Been a trooper for many years and want to get it back and reliably running for the winter. Here's the history of my problem and any help would be greatly appreciated, I'm tearing my hair out.

Summer months I was only driving the Comanche a few times. Back then I found that when I stopped it after it got hot it would have trouble restarting, but eventually would. This has progressively got worse to a point now when it starts when cold runs about 5 minutes then stalls. Won't restart until it cools down again. I already replaced the CPS, which I though was the problem. Had one from non-delaer and still the problem existed so I replaced with a dealer part. No change, still have the same problem and I don't think it can be this anymore after haveing two new ones in. Some history here, I did yank the wires out of the connector a while back when doing a clutch change and had to replace the connector for the CPS. I can't see this being a problem, but I thought I'd add that in since I'm having no luck finding what's wrong. I've looked on-line and checked some other simple items out. I replaced the Ignition switch mounted on the lower steering column but that produced no change. I also replaced the battery leads since I thought a bad ground might be the problem and I had found some worn insulation on them, still no change.

It runs fine when it first starts cold. I notice it hiccup a time or two, then it'll stall and not restart until it cools. When I was able to have it on the road, it would sometimes recover from the stall if I would just keep giving it gas (pumping the pedal). I though for a while it was fuel but have since ruled that out (40psi on the rail). I also put in new plugs, wires, cap and rotor with no change. What can I do next? It seems like some electrical problem to me, but I'm not sure where to turn next. I've read about IAC's, ICM's, and PMU's and don't know for sure which apply to me. Are these potential problems?

jb

I have seen other posts on here that said it could the IAC, which is located on the front of the throttle body.
The Haynes manual says that hard starting could also be caused by the camshaft position sensor (also known as pickup coil/stator). Although anytime I have had the pickup coil go out, my Jeep's would not start at all! It located in the distributor, and to replace it you have to pull the distributor.

I Some history here, I did yank the wires out of the connector a while back when doing a clutch change and had to replace the connector for the CPS. I can't see this being a problem, but I thought I'd add that in since I'm having no luck finding what's wrong.
jb

i think i'd shoot the wires on the cps. i'm pretty sure its in the forum somewhere(on what to do). your wires could be chaffed/shorted, i'd check that before i replaced any more sensors....

also check the actual sensor itself, make sure that you didn't gouge the sensor when trying to get it back in the transmission, made that mistake on my '88 Commanche after a clutch job. When I did that, it would start, but it would hiccup and eventually got to the point where it wouldn't start. If you say the connector is bad, go to a junkyard and cut one off from another MJ or XJ and resolder the wires back together.

Well, I feel kinda stupid now but very happy. The problem turned out to be some minor corrosion on the connections between the ignition coil and the ECM. I was finally resolved to take it to a dealer for some diagnostics. When I called, the mechanic suggested pulling the pickup out of the distributor. I called on the part and it was about the same cost as the dealer was going to charge for the scan. However, the guy at the store said he thought it'd be the ECM and that he could test it. When I pulled that I noticed the corroded connection. It wasn't really all that much corrosion, but the coil connections don't seat very far into the ECM. I cleaned them and put some conductive grease on them as well and started it up before taking the ECM to get tested. No stall!!!! Ran great this morning to work and I'm glad to say she's accumulating even more miles now, 356 K and going and going. In my defense for stupidity, I had tested the coil but did it while it was in the truck so I never saw the connections that well at first.

For some more reference, as I was troubleshooting, my CPS measured at ~200 ohms cold and ~ 210 ohms when it stalled. Wasn;t the problem, but maybe can help someone else out. I also was able to disconnect the O2 sensor, TPS sensor, coolant temperature sensor, and MAPS sensor and the truck would still run. That may be a good way to eliminate those as problems for future reference in case they are sending a bad signal to the computer (ie. no sensor input from these won't stop the truck).

BTW Thanks for the replies

John