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| 2 pcms? (Page 1/2) |
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Murphyseiro
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JUN 09, 09:00 PM
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Has anyone ever used 2 pcms (one being stock fiero other being 3800) for their swaps? As someone who’s never done a swap let alone a 3800 swap, I of course jumped right in and have done everything EXCEPT wiring. I took the old motor out put the sc3800 in with the Muncie 4 speed but I am now at the point in the swap that my mechanical brain dies off. I was wondering if anyone else has ran 2 separate pcms the fiero pcm to basically just run whatever like the spedo and stuff and the 3800 one to run just the motor. I have my fuel pump wired to a switch the starter wired to a button and my radiator fan to a switch so that hopefully all the key would be useful for is too unlock the wheel and use lights . So theoretically it could be possible…? Just looking for some insight, I’m trying to finish it up hopefully in the next 2 weeks
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Patrick
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JUN 09, 09:22 PM
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| quote | Originally posted by Murphyseiro:
I have my fuel pump wired to a switch...
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So if you were ever in an accident and knocked unconscious, and the engine was on fire... the fuel pump would just keep going, and feeding the fire? I really really hope that's not what you've done!
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Murphyseiro
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JUN 09, 09:34 PM
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| quote | Originally posted by Patrick:
So if you were ever in an accident and knocked unconscious, and the engine was on fire... the fuel pump would just keep going, and feeding the fire? I really really hope that's not what you've done! |
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Indeed. But, that is worst case scenario. Hopefully that never happens lol.
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fieroguru
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JUN 09, 09:50 PM
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The Fiero doesn't need any ECM for all the gauges, AC, alternator, starter, etc. to work.
There is zero reason to keep the stock Fiero ecm when doing an engine swap that comes with another ecm. Just use the new ECM.
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Patrick
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JUN 09, 10:04 PM
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| quote | Originally posted by Murphyseiro:
Indeed. But, that is worst case scenario. Hopefully that never happens lol.
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No, the worst case scenario is a fiery crash, where the vehicle occupants are incapacitated, trapped... and fully conscious.
Look, nobody expects awful things to happen, but they do occur. I know this is a completely different situation, but two years ago, a new enthusiastic PFF member we welcomed to the forum was killed when his Fiero fell on him. It was really heartbreaking to hear about. 
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Murphyseiro
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JUN 09, 10:22 PM
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| quote | Originally posted by fieroguru:
The Fiero doesn't need any ECM for all the gauges, AC, alternator, starter, etc. to work.
There is zero reason to keep the stock Fiero ecm when doing an engine swap that comes with another ecm. Just use the new ECM.
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Sweet, that’s not so bad then. How would you go about having the pcm turn on then if I didn’t want to wire the ignition to it. Could I wire a switch to the battery 1 fuse on the fuse box for the 3.8? or would it be smarter or easier just to wire the ignition to that portion of it? I didn’t really want to dig into that side of things but if I have to or it’s easier then I will. Or should I honestly just wire a kill switch for the battery for shutting off and no connection
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jelly2m8
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JUN 10, 12:11 AM
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Sounds like a disaster in the making. I would stop where you are, undo what you did with your wiring, throw the switches in the garbage and go to this site and do it properly so it works like a car not a moon lander.
http://www.gmtuners.com/files/index.htm
find the diagrams for your drivetrain and do it this way, it's less complicated, less work.[This message has been edited by jelly2m8 (edited 06-10-2023).]
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reinhart
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JUN 10, 06:46 AM
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| quote | Originally posted by fieroguru:
The Fiero doesn't need any ECM for all the gauges, AC, alternator, starter, etc. to work.
There is zero reason to keep the stock Fiero ecm when doing an engine swap that comes with another ecm. Just use the new ECM.
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This is the correct answer. The only thing that you might have issues with is the Fiero speedometer. You might have to get a VSS converter, but none of the other sensors on the Fiero dash should have a problem with swapping out the ECM.
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olejoedad
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JUN 10, 07:34 AM
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| quote | Originally posted by reinhart:
This is the correct answer. The only thing that you might have issues with is the Fiero speedometer. You might have to get a VSS converter, but none of the other sensors on the Fiero dash should have a problem with swapping out the ECM. |
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Fiero VSS wires to the 3800 PCM, PCM has an output to drive Fiero speedo.
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sanderson231
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JUN 10, 10:35 AM
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| quote | Originally posted by olejoedad:
Fiero VSS wires to the 3800 PCM, PCM has an output to drive Fiero speedo. |
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True but I've always heard that the square wave output of the 3800 PCM needs to be converted to a sine wave for the Fiero speedometer module. So that's what I have done on both a 3800 and 4.9L swap. The circuitry is simple and consists of two resistors and a capacitor. You can build it yourself or one can be bought for $22:
https://reddevilriver.com/h...peedo-buffer-circuit
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formerly known as sanderson
1984 Quad 4
1886 SE 2.8L
1988 4.9L Cadillac
1988 3800 Supercharged[This message has been edited by sanderson231 (edited 06-10-2023).]
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