Help wire speedo after ECM removal
08-05-2013, 08:21 PM
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Car: 87 Pontiac Trans Am
Engine: Lapouttre Racing 350
Transmission: Rebuilt 700r4 Mild shift kit
Axle/Gears: 10 bolt 3.23 posi w/disc brakes
Help wire speedo after ECM removal
Anyone give me a thread or some basics on how to get my speedo working after ECM delete? Car was a 305 CCC computer controlled carb.Also deleted cruise if that matters.... Mechanical needle speedo has the yellow VSS box under the passenger side dash. 700R4 tranny... Been searching and am finding bits and pieces. Might need to buy a dakota digital sgi-5 ? ......thanks
Last edited by Sidethumper; 08-05-2013 at 09:21 PM.
08-06-2013, 02:55 AM
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Car: 82 Z28
Engine: 383 SP EFI/ 4150 TB
Transmission: T400
Axle/Gears: QP 9" 3.73
Re: Help wire speedo after ECM removal
https://www.thirdgen.org/forums/post...690-post2.html
https://www.thirdgen.org/forums/post...968-post3.html
08-06-2013, 03:40 PM
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Car: 87 Pontiac Trans Am
Engine: Lapouttre Racing 350
Transmission: Rebuilt 700r4 Mild shift kit
Axle/Gears: 10 bolt 3.23 posi w/disc brakes
Re: Help wire speedo after ECM removal
On your car the speedo signal goes from the buffer box to the computer so removing the computer should have no effect on the speedo.
https://www.thirdgen.org/forums/post...690-post2.html
https://www.thirdgen.org/forums/post...968-post3.html
https://www.thirdgen.org/forums/post...690-post2.html
https://www.thirdgen.org/forums/post...968-post3.html
08-06-2013, 08:17 PM
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Car: 82 Z28
Engine: 383 SP EFI/ 4150 TB
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Axle/Gears: QP 9" 3.73
Re: Help wire speedo after ECM removal
It only controls the convertor lockup (which you have to re-jig if you delete the computer control).
Have to wait until '94 before you got a computer controlled (shifts ) trans
The speedo however is by a mechanical cable from the trans to the dash ; unaffected by whatever you do to the computer
Have to wait until '94 before you got a computer controlled (shifts ) trans
The speedo however is by a mechanical cable from the trans to the dash ; unaffected by whatever you do to the computer
Last edited by vetteoz; 08-06-2013 at 08:21 PM.
08-06-2013, 08:34 PM
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Car: 86 Trans Am
Engine: 305
Transmission: 700r
Axle/Gears: 9 bolt 2.77
Re: Help wire speedo after ECM removal
I could be wrong but i thought the vss buffer box was grounded through the ecm. Someone please correct me if Im wrong
08-06-2013, 08:39 PM
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Car: 87 Pontiac Trans Am
Engine: Lapouttre Racing 350
Transmission: Rebuilt 700r4 Mild shift kit
Axle/Gears: 10 bolt 3.23 posi w/disc brakes
Re: Help wire speedo after ECM removal
It only controls the convertor lockup (which you have to re-jig if you delete the computer control).
Have to wait until '94 before you got a computer controlled (shifts ) trans
The speedo however is by a mechanical cable from the trans to the dash ; unaffected by whatever you do to the computer
Have to wait until '94 before you got a computer controlled (shifts ) trans
The speedo however is by a mechanical cable from the trans to the dash ; unaffected by whatever you do to the computer
Last edited by Sidethumper; 08-06-2013 at 09:01 PM.
08-07-2013, 11:58 AM
#7
Re: Help wire speedo after ECM removal
Only very 'BASE' 86 Firebirds still used the cable in 86,.... V6 with no gauges for example..... all other cars got the electric VSS.
Looks like the 86 Firbird Speedo buffer gets it's ground from the ground wires that normally get bolted to the back of the heads. If the ECM harness is removed than there's no connection to the C207 connector and no ground circuit leading back to the buffer.
The buffer ground wire ( for 86 with analog cluster ) is run thru the C207 connector pin "M" using a black/white wire. To get the buffer working again ground that pin.
Looks like the 86 Firbird Speedo buffer gets it's ground from the ground wires that normally get bolted to the back of the heads. If the ECM harness is removed than there's no connection to the C207 connector and no ground circuit leading back to the buffer.
The buffer ground wire ( for 86 with analog cluster ) is run thru the C207 connector pin "M" using a black/white wire. To get the buffer working again ground that pin.
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08-07-2013, 02:47 PM
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Car: 87 Pontiac Trans Am
Engine: Lapouttre Racing 350
Transmission: Rebuilt 700r4 Mild shift kit
Axle/Gears: 10 bolt 3.23 posi w/disc brakes
Re: Help wire speedo after ECM removal
Only very 'BASE' 86 Firebirds still used the cable in 86,.... V6 with no gauges for example..... all other cars got the electric VSS.
Looks like the 86 Firbird Speedo buffer gets it's ground from the ground wires that normally get bolted to the back of the heads. If the ECM harness is removed than there's no connection to the C207 connector and no ground circuit leading back to the buffer.
The buffer ground wire ( for 86 with analog cluster ) is run thru the C207 connector pin "M" using a black/white wire. To get the buffer working again ground that pin.
Looks like the 86 Firbird Speedo buffer gets it's ground from the ground wires that normally get bolted to the back of the heads. If the ECM harness is removed than there's no connection to the C207 connector and no ground circuit leading back to the buffer.
The buffer ground wire ( for 86 with analog cluster ) is run thru the C207 connector pin "M" using a black/white wire. To get the buffer working again ground that pin.
Last edited by Sidethumper; 08-07-2013 at 04:06 PM.
08-09-2013, 11:28 AM
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Car: 1986 Pontiac Trans Am
Engine: 350 cid bore too much to list.
Transmission: 700-R4
Re: Help wire speedo after ECM removal
My T/A is an 86' EG4 car and decomputerized the engine (as well as upgraded 
) years ago and never had a interruption with my speedo. Sounds like you have a bad connection somewhere.
) years ago and never had a interruption with my speedo. Sounds like you have a bad connection somewhere. 
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