Pop noise, then Jeep died, now it won't restart

Moellertime

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Nov 20, 2021
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Fort Worth, TX
Hello!

This is my first post on this forum. I have a 1994 Jeep Wrangler YJ Sahara 4.0L with a manual transmission. Driving to work this morning the jeep was running great at about 70mph on the interstate and then I heard a pop noise, the engine lost power, and I coasted to a stop on the side of the interstate. When the pop occurred, my RPM and Speedometer both snapped to 0 and the check engine light came on. When I try to re-start the engine, it turns over just fine but does not start. Interestingly, I also tried to check the OBDI code (with the on-off-on-off-on key method) and the codes will not display, instead the check engine light remains on steadily. I am certain that I am doing this correctly as I have done it before.

I got a buddy to tow me to work and along the way I also tried to let the clutch out with the engine in gear. Once again the engine turns, but does not run. I noticed when I tried this while being towed (with the key in the run position), that the Tachometer and Speedometer both continue to read 0 even though I can hear the engine being turned over. My suspicion is that this could be some sort of PCM or electrical issue given the inability to retrieve trouble codes as well as the inoperability of the tach and speedometer, but I would very much appreciate any input from someone who knows these jeeps better than I as to what the issue might be.

Thanks in advance!
 

redcardinal

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Aug 31, 2021
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I’m not an expert on PCM issues, but when my 95 was giving me CEL problems, I disconnected the battery for an hour or so and reconnected. It cleared the codes, CEL went off, and it started right up. That was over a year ago and I haven’t had any further problems. I’m sure someone with more PCM experience will chime in here, but the disconnect/reconnect might get you home.
RC
 

machoheadgames

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that is unlike any PCM issue I have ever seen anyone experience, the number one failure is the capacitors die and then it won't start (cranks, but does not run), unless you wait for the check engine light to turn on and the PCM to fire up the ASD and fuel pump relays.

the other semi common failure is the alternator voltage regulator goes bad.

HOWEVER, it is an electronic device and can potentially fail in many different ways. I would remove the PCM, take the lid off of it (just a few screws IIRC) and look at the circus board. See if anything looks like it exploded in there. I would think if anything went bad, it should be fairly obvious since you heard a pop loud enough to be audible while on the highway. I bet you'll find the issue in the PCM based on the symptoms.
 

Flyer58

YJ Enthusiast
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Apr 12, 2020
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640
Location
Magnolia, Texas
That pop sounds throws me. I'm first thinking something electrical shorted out and maybe fried some diodes along the line. Or it was the sudden unloading of power on the drivetrain. Do you smell any burnt wires?
 

TimberTim

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Mar 19, 2022
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NorCal
pull a plug wire and check for spark while you turn it over, if you have spark dribble some gas down the carb and see if it fires off, start with the simple things !
 

machoheadgames

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pull a plug wire and check for spark while you turn it over, if you have spark dribble some gas down the carb and see if it fires off, start with the simple things !
He doesn’t have a carb and if his check engine light isn’t coming in when he flips the key then he doesn’t have spark either.
 
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Moellertime

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Nov 20, 2021
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Fort Worth, TX
Thanks for all your replies! I got the PCM back from wranglerfix with a clean bill of health and re-installed it. No change. I'm gonna have it dropped off at a shop today in Aledo and let them figure it out. I'll make sure to have them update me on what they find and report back!
 
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