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1995 Impala SS
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Discussion Starter · #1 ·
So, hypothetically speaking, what if you had 2 different Tunes on 2 different PCMs? Then what if you were able to make a splitter cable that worked as a sort of relay. Instead of off/on, it would change which input would send to the car.

And once you were able to flip it back and forth, you take it for a drive. If you are driving along an empty road and put it in Neutral, shut the car off, coasting and flip the splitter cable so that the other PCM is "active."

Could you turn the key, slip it back into drive and roll on with your 2nd Tune?

Anybody know if that could even work? I mean it sounds functional.
 

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Some signals (MAP, TPS, voltage outputs) you can just parallel to both ECU's. Other signals like resistances (temperature) can't be "shared", and need their own dedicated circuit so would require some sort of switching mechanism (relays for example). Outputs like injector drivers or others that have current monitoring will also need their dedicated switching between ECU's.

Practically it's probably easier and better to move to a more modern ECU architecture that supports multiple maps.

So, while it's technically possible, it's a LOT of wiring and relays/switches that need to be of high quality for dependability/safety

If you look at the below and don't go "F That!" - grab the service manual and make a plan :)

 

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Anything is possible but I bet there are a number of circuits that couldnt be "tee'd" and would need to be actually switched.
Your switching controller might end up being quite elaborate.

Now the question ,,,,, to what end??
A carefully , properly tuned PCM covers most all situations pretty well

Edit : post above lays it out clearer
 

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For about a year, I used to switch between 3 different pcms.
Physically switching pcms is quicker than TunerCAT's WinFlash.
So far as I know, though, only I've ever used a Caprice wagon to teach people how to drive.
The novice student pcm had an annoyingly safe shift table, soft-limited to 4th gear over 56MpH.
The better student pcm had a more reasonable shift table, soft-limited to 4th gear over 70MpH.
Mine was more fun ...

For the past 28 years, every LT1 pcm has had an available secondary 'Performance' shift table.
Yet GM saw fit to only allow '94 & '95 Pontiac FireBirds to physically access it - not Corvettes, not Camaros (B4C or otherwise), not SS, not 9C1s, not even LT1-V4P Fleetwoods which could've gotten better MpGs with it.

Besides GM and myself, over 98% of B- & D- body owners, including nearly every enthusiast, and nearly every ISSF member past and present, never bothered to try to access / use the LT1's secondary shift table.

Despite the past 28 years, caddylack is considering making a longer Performance Mode harness for us.

The LAST thing I want to do with this post is discourage you!
I bet a Performance Mode harness would deliver the functionality you seek, though.
 

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1995 Impala SS
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Discussion Starter · #5 ·
If you look at the below and don't go "F That!" - grab the service manual and make a plan :)
I mean... as long as you can shut the hood, you're good. Right?

Now the question ,,,,, to what end??
To no end, aside from curiosity.

For about a year, I used to switch between 3 different pcms.
Physically switching pcms is quicker than TunerCAT's WinFlash.
Probably something like a situation like this. If you swapped them often enough that you wonder how many more times before you break a connector.

Very enlightening input. Thank you sirs.
 

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"making a longer Performance Mode harness for us"

When there are already wires that go from the PCM to under the dash you could move to that pin ?
 
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