You know... that same exact damn issue drove me CRAZY for an entire summer! I checked every thing, replaced parts, and ran diagnostics with a FSM and test meters. One night when it was wet, for kicks I had one of my boys crank it for me to see if it had spark. I did and just as it went out I saw a tiny spark on the wire of the coil harness. A close exam showed that sometime (at least ten years, because I had the old Jeep that long) somebody had poked the wire with a damn test light! Over the years the wire corroded and was just cutting out on me, and getting worse and worse as time went on. A new plug did the trick though!
Problem was solved for about a day and now I'm back to no spark again.
This time I checked power at the connector to the ignition coil with the ignition key turned to the on position and got 12.5 volts which is good (I think). Next I checked the voltage at the connector while cranking the engine and the voltage was about 6.2 volts. I don't know if this is normal or enough to power the coil and produce spark.
Start it pulls through a resistive line so it should drop. 6.2 is low. It should be around 9. You can jumper battery power to the coil like I mentioned before and see if it starts. Did you ever replace the distributor pickup sensor? What about the CEL, what codes?
Back to where i started. Jeep ran great for a day with the new ignition coil connector plug. I thought this was the problem because if I held the connector tight against the ignition coil the jeep would start right up and run as long as the connector was held. As soon as I removed the pressure on the ignition coil connector plug it would stall out. It was repeatable and I did it at least 10 times. Put the new connector in and it ran like a top for the day and now it won't start again (no spark).
Here's what I've done:
-New crank position sensor
-New distributor and cam position sensor
-New ECM (jeep was running with old and new ECM's)
-Good 12.5 volt power to the ignition coil plug with the key in the on position
-About 6.2 volt power to the ignition coil plug while cranking
-Wired the ignition coil plug directly to the battery and got the same 12.5 volt power to the ignition coil plug and had about 11.2 volts while cranking the engine
-Not sure if it matters but the ECM is getting power thru pins 3 & 9. Pins 11 & 12 had good continuity to ground
-I checked ALL fuses with a multimeter for continuity and they are all good
-I bought a spark tester and I'm showing no spark. I did test it when it was running and the tester is good showing clear blue spark
I'm out of ideas for the moment. Love to hear your thoughts.
I don't believe in coincidences either, but this is my 3rd new ignition coil so 4 different coils if you count the original. I forgot to add the wiring from the ignition coil to the distributor is new and I do have a new cam position sensor (stator) with the new distributor. I some some specs on testing a coil so I'll be checking my old and new coil.
Didn't have time to do much this week except pick up a noid light to check the connector that plugs into the ignition coil. This afternoon checked power using the noid light and it showed good power to the connector. Plugged the connector back into the ignition coil and after a week of sitting, the jeep started right up and is currently running. If it stops running again I'll check the ignition coil plug with the noid light again.
Currently looking for a new engine compartment wire harness. As usual, any ideas are appreciated.
Oh man... you guys are really freakin' me out. My 91 has also been possessed. I'm going to follow you all and see what happens. BTW, I never got my rebuilt ECM from that place in Lauderdale. So, I ordered one from a rebuilder in Jacksonville. After 3 weeks, I asked for my funds back. Distributor 2 years ago, problem cleared up and is back. Not showing codes... threw a crank sensor, coil at it and I was hunting an ECM. 5602 7410 if anyone has a spare. I did look at the board through the insulator and I see something fried. Its coming out and Ill dig into it when I get back from SC... this week. Keep posting fellas, and thank you. I thought I was alone out here.
Hauled my work trailer down from SC, in Orlando again. Jeep quit and thankfully restarted after about 2 mins on side of a winding desolate country road at 2am. 2 days with no issues. looked and there are no additions to this post. Is it done? thx for any help.
Thanks for checking for updates. Here's the latest
My Jeep has been running for almost a month and that's the good news.
I did a lot of electrical trouble shooting with a multi meter. Had about a week where I didn't do anything.
On some advice from the forum I tested the the connector that plugs into the coil with a noid light. I'd never heard of a noid light (it's normally used for checking fuel injectors) but I tried it. It showed I was getting electrical power to the coil connector plug. Tested good twice and I just reconnected the plug to the coil.
The bad news. It started right up with nothing really being done. I suspect an electrical short/break somewhere in the engine compartment wire harness. I've been calling around trying to find a new harness but the 1991 wrangler is unique so no luck yet.
I'm hoping it lasts the summer/fall and maybe I can put the new wire harness in this winter.
Hope this helps a little. I'll update with any changes as they occur.
Well I put the whammy on myself. Jeep stopped running today. So here's the latest.
Same problem, cranks but no ignition. Tried the noid light again but it shows now power to the coil connector. Next checked checked for voltage at the coil connector with a multimeter with the key in the start position (not cranking) and it showed 12.47 volts and good continuity between the ground and the negative battery terminal. I'm stumped again.