Here's the scoop.... I bought a 92-RS with a 305 TBI engine. After having it for a while I picked up and 88 IROC-z with a 350 TPI engine so I swapped engines out. (I put the 88 TPI into my 92 RS) Everything works fine except my speedometer. when I switched the engine, I of couse switched the ECM and all other parts. I repinned the C-100 and added my speedometer wires to it. (rather than the cable) It runs great but my speedometer is completely messed up. When I'm sitting still it's fine at 0-mph, when I move it pegges out to 110 then falls back to 0 then just freely flips around while I'm driving. I have no idea what could have caused this or how to fix it. Along with this problem the torque converter locks early. I'm at a loss for any other ideas that may fix this. I've tried using other speed sensors and they either don't work at all, or do this. Is this a problem with the ECM? or is my speedo ruined? I have no idea I'd like some help if anyone has any ideas.

 

anyone?

 

I would check to see if the VSS is the same for both engines. I just found out that in my car.. which was 89 305tpi T5. I am putting in a 94LT1 .. the VSS is not compatible.. I have to purchase a device to remedy this. or buy a t56 You may have something similar..