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First post to the club, but a frequent user of the great advice you guys offer. Having a crank issue with a 91 4.0 Have power, but as soon as I turn the key completely to ignition I hear one click coming from the starter, the starter is trying to engage but then I lose all power and Can not keep trying to crank until I disconnect the battery and the reconnect to have the same thing happen. Things I’ve checked and or replaced: Starter Starter wires Grounds Ignition switch nss (completely replaced) all relays and fuses battery (used multiple different batteries to be sure) battery terminals and negative and positive terminal clamps radio and speakers (checking for shorts) Fuel pump ballast resistor map sensor and probably a few others that I’m forgetting Probably have about 25 hours in to this problem and I’m at a complete loss. Maybe I messed something up along the way so feel free to give any knowledge of common mistakes made during install or my checks along the way. I hope what I’m trying to say is clear and if not I can clarify

So, I'm building an 87 Comanche. I'm using a 91 HO Cherokee for the engine, transmission, T-case, electrical, dash and so on. Started a awhile back. So, I bought a new CPS sensor. Started installing it. And I'll tell you what, I have quite a few choice words for the guy that decided that location was a good place. I hope he suffers an eternity of having to replace these. On a clean truck, not bad, but on a well driven one... I spent hours trying to get it installed. The dang bolts won't thread in the holes, with sensor. But, sure as hell, I can hand thread with out the sensor. put the sensor back, and put the bolts in, turn for F-N hours, and never grab a thread. Well finally get dat b!tch up, and start to connect it. I can't find the matching connector on the harness! W.T.F!!! I've read there may have been a service bulletin to relocate connector to inside the cab. Take dash apart, and I can't locate a matching connector. I have 3 other XJ / MJ's to compare. 2000 XJ, CPS looks like it connects to harness with the transmission on passenger side. My 91/87 MJ no have that... 1990 MJ, CPS is connected to a GM style connector off the injector harness. My 91/87 MJ no have that same style plug.. Now, there is an un used round 3 pin connector on the injector harness. I always figured it was for a different TB. So, I goto Autozone, and have them show me a CPS from a 91... Damn it!, looks like it uses a round connector. So, I just spent some time in CPS HELL, and installed the wrong damn sensor... Now, I got to remove that sensor, buy correct one, and pray I can install in less then 8hr... before all this started, I went to a u pull it salvage yard, and pulled a CPS. It only took me 10min to remove it. I wanted to bolts, cause I did not know the size needed, I figured if I was going through the pain of installing a CPS, I may as well start with correct bolts. The F N issue is I could not get the bolts to bite as I turned the wrench. I used paper to make sure the bolt was not sliding down into the socket... Anyway, for thats don't know, there are different plugs on the CPS used. now I know. I'm debating on just cutting both ends off and putting on GM style weather pack connectors.

Please Help, I have a 91 MJ 4L HO with engine electrical issues. I will break it down for ease of ruling stuff out. Engine ran okay when purchased 2 months ago went to restore/build up on it. Tuned up engine New plugs (not platinum, standard plugs) New Wires New Fuel filter New Cap New Rotor Cut Cat Conv out, new 2 and 3/4"exhaust and muffler (not from jeep), Disconnected battery when I welded on new pipes to existing. Engine now idles fine but when put under load (in gear) backfires through throttle body, pukes oil/gas mixture into air box, plugs black, no power, Checked plugs/wires crossed multiple times, checked throttle position sensor, checked resistance on new wires, checked coil, checked under cap for arcing issues, checked seems like everything. Have multiple errors and most are Voltage to muliple sensors are above/below range. I can give a breakdown if that will help you guys? Could some of you more experienced guys tell me if you have had these issues, and where to look next. Fuel Injectors? Seem okay but all plugs are black on all cylinders. Timing out? How do you get back into time? Coil? could the coil be intermitent? would it cause same issues as an engine out of time? I have read that MJ 4L use the cam sensor for timing and that they "can"t go out of time?" Please Help