Tuning a separate ECU and keeping the stock one "stock"
Thread Starter
Heel & Toe
Joined: Dec 2025
Posts: 15
Likes: 0
Tuning a separate ECU and keeping the stock one "stock"
Has anyone ever bought a spare ECU in order to tune it for mods. Thus keeping the factory ECU "pure". Reason being is I want to add some mods(long tube headers, full exhaust and intake, Thus needing a tune). However california is pretty strict on that stuff.
Normally id say just tune it back to stock if you get caught. However Ive seen it first hand where people have tried that and the computers dont actually take the stock files to the exact parameters and still end up failing smog. Only way to fix that was to get a new ECU from a dealer and have GM program it from upstairs.
So I want to have a fall back just in case something does happen. That way my stock ECU would still retain smog passing software. Wondering if anyone has done this ECU swap thing, what it takes and where to even get one. 04 Z06 Thanks!
Normally id say just tune it back to stock if you get caught. However Ive seen it first hand where people have tried that and the computers dont actually take the stock files to the exact parameters and still end up failing smog. Only way to fix that was to get a new ECU from a dealer and have GM program it from upstairs.
So I want to have a fall back just in case something does happen. That way my stock ECU would still retain smog passing software. Wondering if anyone has done this ECU swap thing, what it takes and where to even get one. 04 Z06 Thanks!
Safety Car
Joined: Mar 2017
Posts: 3,759
Likes: 935
From: Orlando Florida
I have not changed mine, but find the idea very appealing and will be following to see where this ends up.
What year is your car? I see 99 and up are pretty available, but 97 and 98 many dollars.
i also see “Flagship One” says they have pre-programmed units for $209
What year is your car? I see 99 and up are pretty available, but 97 and 98 many dollars.
i also see “Flagship One” says they have pre-programmed units for $209
Melting Slicks
Joined: Feb 2001
Posts: 2,799
Likes: 356
From: Northville, MI
more information
Waste of money. If you have someone program your PCM then ask for a download of the original on a memory stick. If you every want to go back to stock in the future have the programmer use you memory stick and no problem to do it.
the PCM has 512 bits of information of which about 100 are programmable and the remaining 400+ are firmware. The 2004 has 1mp of information but only 100+ are programmable. The C5 has a 16mb computer and the C6 went to a 32mb and the following generations used 64,128.etc. computing systems. Yes the C5 used a IBM PS2 chip
the PCM has 512 bits of information of which about 100 are programmable and the remaining 400+ are firmware. The 2004 has 1mp of information but only 100+ are programmable. The C5 has a 16mb computer and the C6 went to a 32mb and the following generations used 64,128.etc. computing systems. Yes the C5 used a IBM PS2 chip
Last edited by Gordy M; Yesterday at 09:29 AM.
Drifting
Joined: Feb 2025
Posts: 1,907
Likes: 1,878
From: THE BEACH..
I think moving out of California would be less work than it would be to swap out a PCM every time you go in for an inspection.
That's ridiculous.
You do a bunch of mods to the car that require a Tune to make it right, hence the Tune in the first place, put the stock PCM back in there it's going to throw a light because things are off such as airflow parameters and a few other things.
Wouldn't really help.
That's ridiculous.
You do a bunch of mods to the car that require a Tune to make it right, hence the Tune in the first place, put the stock PCM back in there it's going to throw a light because things are off such as airflow parameters and a few other things.
Wouldn't really help.
Last edited by the_merv; Yesterday at 09:39 AM.
Drifting
Joined: Sep 2022
Posts: 1,314
Likes: 981
Has anyone ever bought a spare ECU in order to tune it for mods. Thus keeping the factory ECU "pure". Reason being is I want to add some mods(long tube headers, full exhaust and intake, Thus needing a tune). However california is pretty strict on that stuff.
Normally id say just tune it back to stock if you get caught. However Ive seen it first hand where people have tried that and the computers dont actually take the stock files to the exact parameters and still end up failing smog. Only way to fix that was to get a new ECU from a dealer and have GM program it from upstairs.
So I want to have a fall back just in case something does happen. That way my stock ECU would still retain smog passing software. Wondering if anyone has done this ECU swap thing, what it takes and where to even get one. 04 Z06 Thanks!
Normally id say just tune it back to stock if you get caught. However Ive seen it first hand where people have tried that and the computers dont actually take the stock files to the exact parameters and still end up failing smog. Only way to fix that was to get a new ECU from a dealer and have GM program it from upstairs.
So I want to have a fall back just in case something does happen. That way my stock ECU would still retain smog passing software. Wondering if anyone has done this ECU swap thing, what it takes and where to even get one. 04 Z06 Thanks!
I think moving out of California would be less work than it would be to swap out a PCM every time you go in for an inspection.
That's ridiculous.
You do a bunch of mods to the car that require a Tune to make it right, hence the Tune in the first place, put the stock PCM back in there it's going to throw a light because things are off such as airflow parameters and a few other things.
Wouldn't really help.
That's ridiculous.
You do a bunch of mods to the car that require a Tune to make it right, hence the Tune in the first place, put the stock PCM back in there it's going to throw a light because things are off such as airflow parameters and a few other things.
Wouldn't really help.
All that stuff you are adding that needs a tune to operate properly, won't pass california smog either, are you going to put everything back to stock each time you have to get the car smogged???
Terrible plan.
Safety Car
Joined: Nov 2013
Posts: 3,554
Likes: 1,096
From: Ex DPRK, now just N of Medford, OR
I'll take the counterpoint on that...
Catted headers and an intake shouldn't effect the low speed operation enough to throw the CEL.
A cam... yes. Even a fairly mild one would probably need some adjustments to idle speed and mix to stop it throwing misfire faults.
If you can find a smog shop oblivious enough to overlook a set of headers...Go for it!
I found a pre-programmed one for my C6 on ebay.
Catted headers and an intake shouldn't effect the low speed operation enough to throw the CEL.
A cam... yes. Even a fairly mild one would probably need some adjustments to idle speed and mix to stop it throwing misfire faults.
If you can find a smog shop oblivious enough to overlook a set of headers...Go for it!
I found a pre-programmed one for my C6 on ebay.
No Hostility Be Happy
Joined: Aug 2018
Posts: 10,006
Likes: 7,308
From: South Hill Wa
2022 C5 of the Year Finalist - Modified
2021 C5 of the Year Finalist - Modified
Waste of money. If you have someone program your PCM then ask for a download of the original on a memory stick. If you every want to go back to stock in the future have the programmer use you memory stick and no problem to do it.
the PCM has 512 bits of information of which about 100 are programmable and the remaining 400+ are firmware. The 2004 has 1mp of information but only 100+ are programmable. The C5 has a 16mb computer and the C6 went to a 32mb and the following generations used 64,128.etc. computing systems. Yes the C5 used a IBM PS2 chip
the PCM has 512 bits of information of which about 100 are programmable and the remaining 400+ are firmware. The 2004 has 1mp of information but only 100+ are programmable. The C5 has a 16mb computer and the C6 went to a 32mb and the following generations used 64,128.etc. computing systems. Yes the C5 used a IBM PS2 chip
He has an 04 Z which should have the P59 PCM? How does that fit in your architecture map?
OP, I see some flaws in your plan that are going to make this unrealistic for what you are trying to do.
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