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Old 05-07-2014, 10:37 AM   #1
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Engine Problem/Electrical?

Just got a 91 Jeep Wrangler, 4.0l 6cyl for my girls. After having it a day it would not start, no spark. Pulled distributor cap and cleaned it started right up. They drove it the next day, running rough, lost power in 4th and started backfiring and died. Other than suggesting a usual tune up does anyone have any input on what the problem could be?

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Old 05-07-2014, 10:55 AM   #2
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Sorry, I don't have the answers, hopefully someone will chime in soon.

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Old 05-07-2014, 01:20 PM   #3
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This is what I would do. And have done. 1st- check and replace any and all fuses.
2nd- battery clean terminals. Baking soda and water works.
3rd- check all your grounds. Ground to engine from batt, on fire wall to bolt on head (at back of valve cover)
4th-wires to coil. Check they're tight.
5th-tune up,& check the wire going from coil to distributor. Could have been pulled apart inside from wire to metal end you stick into hole. (I've done that before) swap it for another to see if that's it.
That's all there is that makes it run. Oh! You have a ignition module under the radiator over flow. And that's it. One of those thing should fix or point you in right direction. Hope that helps.
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Old 05-07-2014, 01:22 PM   #4
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Test the Cam Sensor (aka pickup coil) in the distributor. Could be going bad.
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Old 05-07-2014, 10:09 PM   #5
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Wierd. I pulled the #1 spark plug. plugged into wire held it to ground, turned it over until it sparked and ran on 5 remaining cylinders. I turned off engine, replaced plug and wire and it would run until warm (about 185 degrees) then it dies. You can pull #1 spark plug again turn it over till it sparks, replace plug and it will start and run again for a few minutes. Im thinking crankshaft position sensor??? any ideas?
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Old 05-08-2014, 09:29 AM   #6
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Also, I did the key on - key off -count the blinking light trick and got codes 12 and 17(lost power and engine stays cold too long -bad thermostat)
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Old 05-08-2014, 10:09 AM   #7
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Code 17 could also be caused by the Temp sensor for the computer. If that is bad (but thinks it's good) that could cause all sorts of issues happen.

But if having spark related issues I would think Coil, Cam Sensor, or just a bad cap and rotor. Or as you mentioned a failing crank sensor (it's been my experience though that crank sensors just go kaput and stay there....but not always lol).
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Old 05-08-2014, 05:43 PM   #8
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I have replaced cap & rotor.Coil is almost brand new.The engine is a 95 4.0 and has fairly new wiring harness (for a 91). Plugs look good and are properly gapped . Plug wires are fairly new. I cleaned and checked fuses,relays, battery terminals and grounds. I was thinking that the 17 code might be because i have after market gauges and the stock temp wire is abandoned. Crankshaft position sensor should be in by morning. Hope that's it. Is there a test for the cam position sensor ? visually it looks to be in good shape.
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Old 05-08-2014, 06:09 PM   #9
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Camshaft Sensor Test (I know it says Cherokee but its the same sensor):
Jeep Cherokee Engines - Camshaft Position Sensor / Sync Pulse (Stator) Diagnostics


There are 2 sensors for the temp. One is on the back of the head. That one is for your gauges. The other is on the Thermostat Housing and is strictly for the computer. The computer bases ALL it's info on that reading and if it's not working right it will be trying to run in a different mode than what it should be.

Heres the testing procedure for the Thermostat Housing one:
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Old 05-10-2014, 11:00 AM   #10
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OK. Crank position sensor wasn't it.It ran for about 5 seconds then died. It has intermittent spark.I swapped out the coil and camshaft sensor from a running 94' jeep and it still didn't run. Then swapped it back to the 94' , the 94' runs great.So I'm sure that my coil and camshaft position sensor are good.What about the ignition module ? Oh yeah, and now I'm only getting a 12 code.
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Old 05-10-2014, 09:17 PM   #11
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UGG now no spark at all. Any ideas?
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Old 05-10-2014, 09:29 PM   #12
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I read somewhere recently someone else having a spark issue. (S)he traced the coil wire backwards and found a ground wire almost corroded in half. It was hidden behind something. I'll see if I can find the post again....And after dinner I'll see what else I can find but you might be correct about the module. Only things left for no spark that you have checked is the wiring and module lol.
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Old 05-11-2014, 12:35 AM   #13
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Yeah I posted that I traced the wires across the engine bay determining that the ground wire goin to icm. The wire was shortin out on the lip just below icm. What a bitch to find. Pulled wire loom apart and spent the day (several hrs ). Sometimes would work and then without warning cut out. Embarrassing, great looking yj dead in middle of road. Got home and tore it apart till I found. P.I.T.A. but worth it. Prob solved. Good luck.

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Old 05-11-2014, 01:36 AM   #14
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Thanks BigDaddy for chiming in. After dinner my injury was bothering me and took a pill, went to lala land, and promptly forgot about this thread till now LOL.
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Old 05-11-2014, 08:15 AM   #15
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ok great thanks. Will look closer at wiring today. PITA is right! I hear ya, nice looking jeep along side the road..... I was at work, daughters were driving it, had to have them towed. Also, have a 94 jeep wrangler at home (that runs great)the ECM looks the same would it hurt to pull that one and put it in the other jeep (91 jeep but 95 engine)? Do you have any idea what causes the ECM to go bad?
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Old 05-12-2014, 09:10 PM   #16
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Found loose wire on solenoid the wire from solenoid to battery. After tightening it up it would start every time no problem. drove it and it would die like it was running out of gas. After it was heated we hit the throttle it would crap out. So we keep the TPS cool with ice and could not get the jeep to die. So we thought we would change the TPS and that would solve to problem. Guess what? Now, for no reason, we dont have spark again. Beginning to think we have a gremlin.
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Old 05-14-2014, 06:13 PM   #17
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After replacing the TPS and could not get it to start. Disconnected battery overnight. Next day connected battery. Jeep starts right up. Drove it about 10 miles no problems. Continues to start and run with no problems. Could it have been as easy as replacing the TPS and resetting computer by disconnecting the battery?

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