94 2.5 in a 91 YJ....need help - Jeep Wrangler Forum

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Old 03-30-2012, 06:58 PM   #1
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94 2.5 in a 91 YJ....need help

I posted a question about this before but really never got an answer. I have a 91 YJ that was originally a 2.5 5spd. the engine was replaced with a 94 2.5. It was running fine but just stopped (after 10k+ miles) after troubleshooting it, it turns out that it needs a computer. my problem is should I order the computer for a 1991 or a 1994 YJ? Or are they the same for certain years (like 1990 to 2012 *just using those years as an example I know it wouldnt be that big of a coverage period). I really need to know if somebody knows for certain what computer to use.
Thanks for the help. This is a great forum, lots of useful info on here!
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Old 03-30-2012, 07:01 PM   #2
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Order the ECM you need for your year Jeep. The 1991-1995 Jeeps share the same basic components and layout.


2.5L Genius of some sort.
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Old 03-30-2012, 07:10 PM   #3
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It depends on how it was swapped and it sounds like you didn't do it. They could have just swapped the block and re-used all the '91 components or it could be all '94.

I'd check to see if you still have a cable-drive speedo, if you do then buy a '91 PCM and only the '91. If the speedo is electric a '92 to '95 PCM should work fine. Make sure you get one for a 5-spd if that's what you're running.
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Old 03-30-2012, 07:58 PM   #4
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use what you had

You should be able to pull the numbers off the failed one and replace with the same part number?
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Old 03-31-2012, 11:32 AM   #5
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Call the dealer and tell them your situation, sometimes newer ecm's have updates from previous years to solve known fuel management issues. Was your swap "complete"? intake and exhaust sensors and actuators? The ecm only manages intake and exhaust, not the engine itself. Oops, silly me I forgot about cam and crank signals. Are the tone rings different for those years?
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Old 03-31-2012, 03:01 PM   #6
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I didnt do the engine swap i bought the jeep with the 94 engine already in it. when they did the swap for whatever reason they didnt use just the block/head. They used all the components from the 94. I know this because when I needed a distributor pick-up the 91 and 94 are different distributors. I am having the problem (that seems to be discussed much on wrangler forums) with the intermittent no start/no CEL. It will at times crank until the battery dies other times it starts right up then I will drive it for awhile and it starts to die. It then gets to the point where it wont start/run at all. If I leave it sit for a few days it usually starts up again and the circle continues. I cant just use the computer thatsin it now 'cause when this originally happened(while I was out of state visiting my parents) the mechanic there put a used ECM in and it was ok for awhile but its back now. Its frustrating! Im almost to the point where I m goin to give up. I tried reading over the FAQ either on this site or jeepforums.com where it explains the steps to try and narrow down a short or the need for a new computer but I could only scratch my head and wonder at all the steps it was talking about. Im just going to replace the computer and hope that fixes it. Anybody have any other suggestions? Ive replaced the fuel pump, fuel pressure reg, starter, ignition switch, map sensor, dist pick-up, crank sensor, ASD sensor and camshaft sensor and still have the same trouble. ( all codes that were thrown by the computer at one time or another)

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