Allright guys, need some help here. A little background info first. The car is a 1992 RS 305. It has an aftermarket (TCI) trans, and has been converted to TPI. I replaced the trans first, had to change tailshaft housing to accomodate torque arm, no other issues. Speedo and Odo worked fine. For the TPI conversion, I used parts, wiring, and computer from running 92 z28 (car was badly wrecked). Everything works, even the cruise control, but the speedometer and odometer are inop. All connections look ok, the cluster was never removed. Can't figure out why it would not work. The speedometer in the donor car worked fine before I removed its TPI system.
Any suggestions? What do I need to check? Are the VSS's different from RS to Z28? I'm really lost, so any help is appreciated.
Thanks.
Dave

 

When it comes to the speed sensor, a TBI car is wired a little different from a TPI (V8 or V6) car. Don't ask me why.

On your TBI car, the VSS signal goes to a "Buffer Box" which divides and adapts the signal to send it to different places, like the cruise control module, the ECM and the speedometer.
(diagram)

On a TPI car, the VSS signal goes straight to the ECM where it is divided and adapted to go to the cruise control module and speedometer.
(diagram)

On both cars, the speed signal passes through different pins of the C207.
What did you do with the C207 connector when you swapped from TBI to TPI?

Judging from your cruise control working, I'd say your buffer box is still operational. You just need to route the VSS signal from it to the ECM (which in turn will send it to the speedometer).

Hope this helps.
Lou

 

What is the C207 connector and where is it located.

Here's a little more info about the TPI swap. Since I had a running donor, I used the TPI hardware itself, all the sensors (except the knock sensor, bought a new one), complete uncut wiring harness, which included the connectors for TC lockup (which I don't use because of my aftermarket tranny) and VSS.
I swapped the hardware onto the engine, replacing all the wiring harness with what came from the donor car, romoving my TBI harness completely. The computer is mounted under the passenger dash, with engine controls plugged in one side, and a interior harness plugged in the other. It was a smooth, easy swap, and it started on the first crank, but the speedo hasn't worked since. It worked in the donor car, so if my cluster or something is different, I just need to know where to look and what to do.
Thanks for the help!
Dave

 

That's the C207.

To be clear, it's the connector between the ECM and dash. It supplies the ECM with power and carries some extra signals.

Your problem lies in different pinouts used on this connector for TBI and TPI. The connector might look the same but the wires don't match up 100%. That explains perfectly why the speedometer doesn't work.

You need to go through the wiring diagrams for both engines and find out which pins carry the VSS signal on each model and what pins you need to more/swap in the connector. That should be enough to get your speedometer working.

If I have a minute, I'll look at it myself.
Lou

P.S.: Isn't there a whole article on TBI->TPI swap? I'd hope it would include the C207 repinning procedure.

 

OK. That definately points me in the right direction. Everything else is working fine, so if I can figure out what needs to be swapped in that connector, I'll be golden.
There is an article on the swap, I didn't even think to read it. I did this swap on my own, before I joined this site. I consider myself pretty handy in the garage, but this has had my baffled since day 1. I had some other problems with the car, and its been sitting for a looong time. Just decided to fix it up recently, and remembered this and I'd like to fix it.
I'll find that article and check for the repinning proc.
Thanks again for all your help!!!
-Dave

 

Lou, thanks for pointing me in the right direction. I found a gray wire coming from the ECM and connected it to the brown wire on the VSS buffer (terminal C). All is well, speedo and odo work good as new.
If you're ever in Cincinnati, look me up and I'll buy you a beer!
-Dave

 

No problem, glad I could help.

But let me ask you a quick question if you don't mind. When you swapped the engine harness, did you unplug the VSS sensor and replace those wires too?

Lou

 

Yep. The new harness had the VSS connector. I think I know where you're going with this, and come to think of it, maybe my cruise doens't work after all... can't remember, car has been sitting for a while.
Dave

 

haven't been around here in awhile,very glad you got everything figured out. BigBabyLou is the man!