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

 

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

 

Have no clue then what the problem could be. I thought the computer controlled the transmission functions? Anyone else have some info?

 

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

 

I could be wrong but i thought the vss buffer box was grounded through the ecm. Someone please correct me if Im wrong

 

The lockout has been re jiged lol. But there is no cable from the trans to the dash . There is only a 2 pin wire at the tail of the tranny, the 4 pin for lockout and the kickdown or TV cable and that is all.

 

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.

 

PRESTO ! Just as simple as that ! Thank you kind Sir... works like a charm. Its probably off due to Rear end change but That's OK for now.

 

Glad to help !

 

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.