PCM Swap... Is it possible? Should it be done or just get the current one reflashed? - JeepForum.com
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post #1 of 7 Old 02-20-2020, 06:05 AM Thread Starter
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2000 WJ 
Join Date: Dec 2019
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PCM Swap... Is it possible? Should it be done or just get the current one reflashed?

Sportin a '00 4.7 with Quadra Trac (for now) and 190,000 miles (the engine is a newer crate engine put in by previous owner, up to about 20,000 miles on it now).

So far I haven't had any issues that would indicate my PCM is going bad. But in researching what all i can do to improve my Frankenstein WJ and make it the best daily driver I can, it seems that updating the PCM or reflashing it is a thing I could do. I've been using a '99 WJ 4.7 as a parts jeep, mainly for it's axles and interior bits. But in looking thru the engine bay for anything else I can put to use, I noticed the PCM had a couple stickers from the dealership indicating it had been flash updated as part of a recall or something. I'm wondering if this might mean this PCM could be better than my current one which does not seem to have ny updates. So...

1) Am I correct to think the PCM's can be updated/reflashed and therefore improve milage or even change the 45RFE to the 54RFE?

2) If I'm not having any problems, should I just leave it be and save the donor PCM for another day?

3) I did try swapping the PCM, the ignition cylinder, the SKIM sensor, and the Master key. It started up and ran great. Or so I thought. As I drove for a couple errands it seemed like the shifting points were different and thiings were better. But then a clunk in the back and the transmission shifted down a gear, stayed there, and eventually stalled out. I barely got it started again, it kept stalling, so I put it into 2 low and crawled my way home at 15mph. Super fun morning lol.

Am I way off base in my understanding here? Do I also need to swap over the TCM as well? I'll try to update with a couple pics of the 2 PCM's.

Thanks in advance for any and all thoughts and advice.

ClownInAJeep is offline  
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post #2 of 7 Old 02-21-2020, 04:45 AM
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1. No, three different hardware / software configurations from the time the 99 was introduced through the end of 2000 with compatibility issues on the critical driver functions.

2. Don't screw around with electronics on a 20 year old ride that aren't already broken. Walking sucks.

3. See #2.
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post #3 of 7 Old 02-21-2020, 09:19 AM
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See above. If its not broke. You cant fix it or make it better. You can not "improve mileage" buy re-flashing a PCM.
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post #4 of 7 Old 02-21-2020, 10:48 AM
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2001 WJ 
Join Date: Mar 2015
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Another vote for leaving it alone. There's no advantage to be had by updating or swapping the PCM. The PCM on these cars give folks enough trouble as is.

Look into SuperChips engine tunes. There's a few different options for running higher octane fuel or maximizing mpg. The gains are minimal, but it should scratch your itch to tinker

Programmers don't die, they just lose their memory!

His: 2001 WJ I6
Hers: 2011 WK2 V6
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post #5 of 7 Old 02-22-2020, 11:40 AM Thread Starter
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Thanks for the replies! I've have definitely come across many threads talking about the troubles the PCMs can sometimes give, or sometimes become the scapegoat. It all started for me with a no start issue I had several months back. Of the many similar problems testamonies I read ranging in every possible cause for the problem, I thought I was seeing bits and pieces of suggestions to replace it out or something. For me, the no start was as simple as loose terminals on the battery. Once I realized what securely tight actually felt like, I haven't had the no start ever since (fingers always crossed lol).

Original setup shall remain. Much appreciated!
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post #6 of 7 Old 02-22-2020, 12:16 PM
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For what it's worth, about 1/3 of the pcm's I reflash for forum member's here are for a crank no start condition after we take the time to troubleshoot it's a common problem.
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post #7 of 7 Old 02-22-2020, 03:03 PM
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Keep the spare parts for WHEN you have trouble down the road. Waterluver can program the spare PCM to work in your jeep plug and play. Then just shelve it till you need it.

I do believe there is a reflash program that the dealer can do to make the 45RFE use the extra hidden gear to make it operate like a trans from a later model WJ. The 45RFE and the 54RFE are supposed to be the exact same trans, just with different programing. (i believe the change happened when the external TCM's disappeared in the 2002 model year, but dont take my word for it)This IS supposed to help with fuel mileage and performance. But i don't think that the 2004 models are just killing it on fuel mileage compared to the 99-2000 models. But every little bit helps. I plan to look into this myself when i get a little more time.

'00LMTD-4.7l,242hd,D30,D44A,3.73's,True-trac front,Spartan rear,3"BBfront,2"BBrear,JK'sW/32's
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