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Unread 03-05-2013, 01:25 PM   #1
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1990 YJ Wrangler 
Join Date: Jan 2006
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Flashing an ECM

I read through a couple of EFI threads and never saw anything about reflashing the computer. But right now I'm contemplating switching out the ECM on my daughters 97 sunfire GT. Every source says that it will need to be flashed in order to work. How can you pull a GM ECM off of a chevy and assume it will work on a 4.2 Jeep.

Has anyone ever dealt with reflashing and is the only option going to a GM dealer?

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Unread 03-05-2013, 01:49 PM   #2
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The GM swap has worked because they're coming from 4.3L engines which are similar enough to not require reprogramming.
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Unread 03-05-2013, 02:46 PM   #3
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More than you want to know about chip programming is over on Binder Planet. You can buy most everything from Moates, or make your own....depends on what you want to do. Go here

A tune from a 4.3 will work pretty well on the 4.2, but you may need to make some adjustments. In my case all the numbers from the run file looked good but I made a slight adjustment to the fuel pressure and things were pretty balanced after that. If it is really off, there are also any number of companies out there that will take a run file from you and then burn you a tune to correct what they see on the run file for about $100. If you want a custom tune, that is they give you one tune, then you run it, they tweak it and so on until you are satisfied with the results, there are several companies out there that will do that work for about $300 or so.
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Unread 03-05-2013, 08:49 PM   #4
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Don't forget that many of the 90's GM computers had a pesky little security thing called VATS....you take the computer out of the GM and drop it in the Jeep without having the rest of the system and it wont even start. I had that issue with my 4.3 swap and had to get it reflashed to remove it and a few other things.
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Unread 03-06-2013, 05:32 AM   #5
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1989 YJ Wrangler 
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On the 4.2L or did you mean a 4.0L? The ECU from the Chevy on a Jeep? More info please. I thought I had seen and done all that could be done electrical and now something new! The Chrysler ECU is not flashable for all practicle purposes.
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