Mechanical Questions

New to Jeeps

New to Jeeps

New Member
Joined
Feb 10, 2024
Messages
18
Location
Florida
Hey guys, I had the wiring to my 92 yj replaced and and it finally runs and drives 😅.
I towed it home from the mechanic because I knew it needing some tlc after sitting for a few months and didn’t want to risk breaking something. It had barely any coolant in the system when I went to drain it so I bought some Prestone radiator flush + cleaner. The bottle recommends for a thorough cleaning to run the engine on idle for 3-6 hours, I got to 2 hours and 3 minutes when I noticed the battery smoking (it was just a little steam but still enough for me to slightly panic and turn off the engine). My dad said it probably ran out of water is all, so the next day I filled it up with water and ran the engine. It wasn’t long before it did the same thing, so I turned the engine off. I thought it was the battery so I put my other battery in (which was dead so I had to jump start it) I tested the voltage when I got it running and the battery read 17 volts while running but 12.1 while off, so I knew it wasn’t the battery.

So I bought a knew alternator which is 90amps (I don’t know the amperage of the old one yet but I’ll be taking it to autozone tomorrow to find out) I installed the new one today and started it up and the battery still reads 17 volts…. Is this normal for a 1992 4.0L yj? And if not, do any of you know a fix? If the old alternator turns out to be a 90 amp one I can only assume that I need to buy a higher amperage alternator like a 136 amp. If that is the fix, will I also need to replace the alternator wires for bigger ones? Thank you guys in advance for your advice
 
No, its not normal. Th ECM regulates the alternators charging output. It has nothing to do with the alternators charging abilities. Not having a clue what the "new wiring" entails, the wiring could be wrong, or your ecm has problems. You should see 13.8 to 14.3V with it running.
 
Gilaguy23 said:
No, its not normal. Th ECM regulates the alternators charging output. It has nothing to do with the alternators charging abilities. Not having a clue what the "new wiring" entails, the wiring could be wrong, or your ecm has problems. You should see 13.8 to 14.3V with it running.
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That’s what I thought. I had the wiring harness replaced because it had electrical issues. The mechanic who replaced the wiring replaced it with a 93 yj harness. I have a warranty on the ecm so I’ll probably send it back to them. Quick question though, does a 1992 yj have an ECM, ECU, PCM, or does it just have a SBEC?
 
Gilaguy23 said:
Im no electronics expert but I think much of that is semantics. Same part, different name. Most guys say www.wranglerfix.com is the way to go for ecm fixes. Perhaps macho will kick in with some knowledge. He puts these together in his sleep ;)
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Got my ecm back from wrangler fix and my battery now reads 13.8volts as opposed to the 17volts before. Now that the electrical issue has been solved there’s just a few more things till I can put this Jeep on the road. Thank you for your help
 
New to Jeeps said:
That’s what I thought. I had the wiring harness replaced because it had electrical issues. The mechanic who replaced the wiring replaced it with a 93 yj harness. I have a warranty on the ecm so I’ll probably send it back to them. Quick question though, does a 1992 yj have an ECM, ECU, PCM, or does it just have a SBEC?
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For the record, most all of those acronyms you listed are synonymous.

ECM - Engine Control Module
PCM - Powertrain Control Module
ECU - Electronic Control Unit (typically)
SBEC - single board engine controller

The YJ engine computer is referred to as a PCM by Mopar. Typically, a PCM is one that controls the "powertrain" as opposed to one that just controls the engine like an ECM. So technically, on a YJ, it should be an ECM. I refer to it as a PCM because that is what the factory service manual calls it. Figure it's easier that way than saying ECM and somebody goes looking for ECM and only ever sees PCM in the book.

SBEC is the type of ECM/PCM utilized by Chrysler. A YJ PCM/ECM is an SBEC type. JTEC (jeep truck engine controller) is another PCM type, and is what TJs used up until around 2005 or so if I remembver right. At that point they switched to NGCs, or Next gen controller. I believe to this day, or at least through the JK, they kept using new and improved variations of NGCs. Not sure if they still are in the JL, but wouldn't be surprised if they are.

ECU is kind of the same thing, it's a control unit like anything else, but in modern cars they use ECUs all over. My Toyota has a skid control ECU, body ECU, 4WD ECU, etc. Basically the modern vehicles have brains (ECUs) all over the vehicle for controlling various different tasks and those all talk on the CAN network. They are all referred to as ECUs by most manufacturers.

New to Jeeps said:
Got my ecm back from wrangler fix and my battery now reads 13.8volts as opposed to the 17volts before. Now that the electrical issue has been solved there’s just a few more things till I can put this Jeep on the road. Thank you for your help
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That's good, sounds like your voltage regulator inside the PCM was bad and is now fixed. There are also external regulator kits available. They are not as sleek, but they do work and it will become harder to find good PCMs as time goes on and parts get older. I definitely would prefer the internal regulator myself, but if it came down to not being able to find a good PCM, I'd go the external route. The better execution of the PCM controlled set up is that it will lower the voltage as temps go up. An external unit is set to one voltage and left there. Which works, but is not as ideal.
 
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