Trying to use a 1991 ecm in a 1993 - JeepForum.com
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post #1 of 17 Old 07-31-2021, 10:50 AM Thread Starter
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Trying to use a 1991 ecm in a 1993

So, here is what is going on. I have a 1993 YJ and the voltage regulator does not work (this is in the computer and not external) I picked up a computer that had been refurbished from a guy on CL. From what I have read 1991 to 1995 should be interchangeable. I hooked it up. It started and the battery showed to be maintaining at 14 volts. I let it idle for about 5 minute or so and then it shut off and would not start again. Has anyone ever come across this happening? Just joined but have been the owner of this Jeep since I bought it new in 1993. Thanks for any help.

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post #2 of 17 Old 07-31-2021, 01:20 PM
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So, here is what is going on. I have a 1993 YJ and the voltage regulator does not work (this is in the computer and not external) I picked up a computer that had been refurbished from a guy on CL. From what I have read 1991 to 1995 should be interchangeable. I hooked it up. It started and the battery showed to be maintaining at 14 volts. I let it idle for about 5 minute or so and then it shut off and would not start again. Has anyone ever come across this happening? Just joined but have been the owner of this Jeep since I bought it new in 1993. Thanks for any help.
The 1991 Jeep YJ has a mechanical speedo, 1993 does not.
The 1991 Jeep YJ ECM is pinned out differently than a 1993 YJ at the bulkhead.

I am sure there are other differences; however, to me, electrical is the devil.

I can get you a 1991 YJ FSM download here: https://www.dropbox.com/s/xa98fp8pjb...%20SM.pdf?dl=0

here is a link to the 1995 (which should be the same as a 1993): https://www.dropbox.com/s/ret5kdafmr...anual.pdf?dl=0

You will need to compare the Pin-Outs for the Bulkhead from the engine bay to the body harness and repin your connectors to mimic the 1993 set up

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post #3 of 17 Old 07-31-2021, 02:04 PM Thread Starter
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Thank you Luuca for the reply. So basically there is probably nothing wrong with the 91’ computer I have, it’s more of a communication. I will probably just sell the 91’ computer and I bought a 95’ one. It just came in and is working. The only thing I have noticed is that the temperature gauge is running at 210. With my old computer it ran lower. I checked the temp in the radiator hoses and they are running cool. The only other question would be, if I send my ECM out for repair would replacing the capacitors fix my voltage regulator problem? This way I have a spare computer just in case. I would rather be dealing with mechanical issues, I hate electrical on cars!!
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post #4 of 17 Old 07-31-2021, 04:11 PM
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The only thing I have noticed is that the temperature gauge is running at 210. With my old computer it ran lower. I checked the temp in the radiator hoses and they are running cool. The only other question would be, if I send my ECM out for repair would replacing the capacitors fix my voltage regulator problem? This way I have a spare computer just in case. I would rather be dealing with mechanical issues, I hate electrical on cars!!
Yes. the temperature may present as lower, but it has nothing to do with the ECM. The temperature guage on the YJs is fed by a separate sensor on the rear of the block near the #6 injector. It is a direct run to the gauge from the sensor. As such, the ECM does not adjust it etc. Chances are, with removing/replacing the ECM, you giggled the wire or the ground to the engine was lessened somehow. Either way, check your engine ground on the passenger side rear of the block and the single wire that is plugged into your Temp Sensor. Make sure the ground is clean and tight and the temp sensor wire is also clean and tight. It really doesn't matter because these engines want to run at 210. You may have actually improved the ground and now its reading correctly.

On the TJ model, there is one fluid temp sender that feeds the ECM and in turn feeds the dash gauge and uses that info to adjust fuel and air trim.

If you send your ECM out for repairs, it should come back working 100%. I would do it if I were you and had the funding to do so.

I'm with you on hating electrical gremlins. Hat it hate it hate it.

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post #5 of 17 Old 07-31-2021, 04:34 PM Thread Starter
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Thank you for the info. Did not know the temp gauge has nothing to do with the ECM. I know the plug your talking about. I’ve replaced almost all the sensors. I resealed everting I could get sealed up. I will look at it again. Thanks again. This is not my daily driver but when the sun is out I want to be able to drive it around with the top off. The way it should be. Lol
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post #6 of 17 Old 07-31-2021, 04:58 PM Thread Starter
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Does you know a good place to send an ECM to have it repaired?
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post #7 of 17 Old 08-01-2021, 08:14 AM
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Good luck with the 1992-1995 ECM. Cardone no longer remanufactures them so gave all the other vendors/individuals a license to steal. I have 1992 that I tried to get repaired-unrepairable have one we can sell for 600 dollars, then tried deadjeep.com used one 325 dollars been in a wreck case destroyed we can send you another one but your third inline. Iím done with SBEC junk. In process installing weber 32/36.
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post #8 of 17 Old 08-01-2021, 03:42 PM
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Here is a link for your '93YJ electrical information

https://drive.google.com/file/d/1jdK...ew?usp=sharing

If I have the information for the '91 ECM pinouts I'll post a link for that also or just the file

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post #9 of 17 Old 08-01-2021, 03:46 PM
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Question for all of the responders. What difference is between the '90YJ and the '91YJ? I know from my old fogged up memory that the '91YJ was an oddball YJ.

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post #10 of 17 Old 08-01-2021, 03:54 PM
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Originally Posted by Jjgator View Post
So, here is what is going on. I have a 1993 YJ and the voltage regulator does not work (this is in the computer and not external) I picked up a computer that had been refurbished from a guy on CL. From what I have read 1991 to 1995 should be interchangeable. I hooked it up. It started and the battery showed to be maintaining at 14 volts. I let it idle for about 5 minute or so and then it shut off and would not start again. Has anyone ever come across this happening? Just joined but have been the owner of this Jeep since I bought it new in 1993. Thanks for any help.
I just had a brain fart. Do you still have your '93YJ ECM? Maybe it has bad capacitors. They can be repaired fairly easy.

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post #11 of 17 Old 08-01-2021, 07:10 PM Thread Starter
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Here is where we am so far on all this. I have 2 ECM’s from a 91 YJ that when I plugged them up they worked for a total of 5 minutes and the Jeep shut off and would not start again. According to most places selling the these 91’ to 95’ should be interchangeable. I am finding that that may not be the case as the pin outs are different on the 91’. I bought another ECU that is from a 95’. It worked fine plug and play. I have been driving around in the Jeep with the 95’ ECU. Right now I want to find a good repair place to get mine repaired if it is repairable. That way I would have a back up. I am not good with a soldering iron or I would just replace the capacitors myself. I don’t want to ruin my original by experimenting on it. If I can find someone local that has a 91’ and I can test the other 2 from the 91’ I will just sell them. My thoughts after all this is go up in year models and you will probably be ok. Thanks everyone for all your help. I know some have said just get rid of the computer, but I have had this Jeep since it was new. First new car I ever bought. I’m just trying to keep as original as I can with a few mods like a lift and wider tires etc..
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post #12 of 17 Old 08-01-2021, 07:35 PM
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I only have a second right now to post. I did not work exclusively on Jeeps in the early to mid 90's but the brands that I did all had one thing in common. If you have a relay or solenoid that is powered by the ECM that has low resistance it can take out an ECM driver. Drivers are what provide most commonly a ground path to activate a device. Some drivers are shared with other things and called quad drivers. So If for instance an EGR solenoid is shorted to ground it can mess up an ECM on other circuits. A loose example.

The terminology from brand to brand changes and I have dealt with this in the dealership level on different occasions. I carries from brand to brand.

What I am saying is..... IF...... and I say IF your info is correct and IF, and I reiterate IF I read this post correctly up to this time. You connect a new ECM all is well for 5 minutes. If that is so, It is not ECMs to blame, you very likely have something that is controlled by the ECM that is shorted or has very low resistance.

You need to differentiate between what the ECM controls and what the ECM sensed to diag this. For example. A TPS will not fix it. It is something that the ECM senses not controls.

I am not 100 sure but if you plug in a new puter and ran good then puked...... Very likely.....

All legal disclamers are now in effect.... going to bed now.... very very long week, weekend, and life. bye bye.

If you cannot fix it with a hammer then it has to be an electrical problem.
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post #13 of 17 Old 08-01-2021, 10:57 PM Thread Starter
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The possibility of something like a solenoid or a relay causing the computer to go bad does concern me. The only thing is that I put a ECM from a 95 Jeep Wrangler in it and it runs fine and I have been driving it around. But, with that being said, is this something that will happen in like 5 minutes or something that could burn out the 95’ ECM over a period of a couple of days. What I’m getting at is, should I be worried about this ECM burning out after driving it around for a couple of weeks. The 2 ECM’s for the 91’ wrangler were the only ones that crapped out in 5minutes. My original computer still works and I can drive the Jeep with it. The only thing wrong with the original computer was that the voltage regulator which is part of the ECU. Thank you for your input. Every little bit can help, especially when chasing electrical gremlins.
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post #14 of 17 Old 08-08-2021, 07:41 AM
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1990 was 4.2, 1991 is the first YJ year for 4.0 and has like four wiring color possibilities.
It’s slightly nutty but it’s doable.

Did the ‘91 ‘puters have a CEL? If so they’re not dead.

Anyway, I might be interested in a spare ‘91 ecm disputer.

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post #15 of 17 Old 08-08-2021, 11:10 AM Thread Starter
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Yes, the CEL came on when I turned the key. It idled for about 5 minutes and just stalled out and wouldn’t start again.
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