After a speed denisty swap on my buddies car, we cant get the speedo to work. We used a brand new harness for a 90-92 Z-28. The VSS is new and also for a 90-92 Z-28.

My question is, is there a VSS buffer box (or whatever it is) on this 89 Formula?

Do we bypass and if so, how?

Or is there something else we may have missed?

Any direction would be appreciated!!

Thanks!

 

Yeah there's a buffer box that you need to bypass.
The VSS signal should go straight into the ECM, and then there are connections for the speedo and cruise off the ECM.

from the VSS - A) yellow wire goes to B10 on the ECM, B) purple wire goes to B9 on the ECM.

From the ECM - B11 brown wire goes to the speedometer ( green with black stripe on buffer box)
- C1 goes to the cruise control ( should be one of the brown wires on the buffer box.. you'll have to test it )

you'll need to locate the buffer box. this link has some info.
http://www.hioutput.com/tech/speedo.html

 

Thank you sir, I will give that a try!

If I run into any problems or if I get it to work, I will post the results.

 

Ok, so what wires do I splice and hook up to bypass this thing?

 

If I just unplug it, will the speedo and the ECM both get VSS signal or will they get none at all?

 

If green/black stripe wire coming out of VSS buffer box is the signal wire going to the speedo, can I clip this wire and splice it into the yellow or purple wire coming from the VSS itself? And if so, which one, yellow or purple?

 

You dont want any wire coming OUT of the buffer box. You want the purple and yellow wires off the VSS in the transmission going directly into the computer, as Jay said.

 

The grn/blk stripe wire that's plugged into the buffer box goes directly to the speedo, right?

Should I remove the box completely or just unplug the yellow/purple (run those to ECM) and then clip grn/blk on buffer box and splice into B11?

On what one the three ECM connectors has B11 - brown?

 

Your SD harness should already have the yellow and purple VSS wires going to pins B9 and B10 at the ECM. The yellow and purple wires that are connected to the buffer box don't have any connection to the VSS at this moment. They just go to the black firewall bulkhead near the brake booster, but there is nothing connected to them on the engine bay side of the firewall.

Pull the box out completely, you don't need it anymore. Splice the speedo wire to pin B11 at the ECM, and splice the red cruise control wire to pin C1 at the ECM like Jay previously mentioned.

Once you do that, you'll have everything working properly.

 

Ok, I removed the Buffer box and connected the grn/blk stripe wire on the VSS buffer box to B11 brown on the ECM.

The speedo still does not move at all !!

I'm using a brand new VSS for a 90-92 Speed Density Z-28/Firebird. Do I need to use the 1989 VSS???

Any help would be appreciated!

 

I finally got the car to through a SES code...

It was code 24 (VSS).

The VSS is brand new from O'reilley's and is for a 90-92 SD TPI 350/auto.

Also, the engine wiring harness is brand new and is installed correctly.

What should I look for or try next?

 

You're not listening to us. You need to do what Jay and 92blue said with the purple and yellow wires.

 

If you have a brand new harness the yellow and purple will already be in the computer plug.
The new harness should have a wire from B11 to the 15 pin connector on the harness,(pin K) from there the wire is going to go to the speedo wire(green/black).

 

Well, the SD harness IS a factory brand new complete harness and does have the purple and yellow plugged into the VSS and Pins B9 and B10 have those wires at the ECM plug in the correct location. I unplugged and removed the buffer box completely and clipped the grn/blk wire off of the buffer box harness connector. I then spliced into B11 brown at the ECM and tied it into the grn/blk wire from the buffer box connector.

So, I hope that was the correct way to wire it. PLEASE correct me if I am wrong, because I'm stuck!

But now the SES code 24 (VSS) just showed up so I think the whole problem is in the VSS somewhere. The VSS that's currently in the tranny is a new VSS for a 90-92 speed density TPI 350 Camaro/Firebird that I bought from O'rielley's back when I originally did the SD swap.

The only thing I can think to do at this point is to pull out the VSS and look at it. Maybe the plastic gear is chewed up or not spinning or something??

What else should I look for or try to do?

 

[quote]The only thing I can think to do at this point is to pull out the VSS and look at it. Maybe the plastic gear is chewed up or not spinning or something??[quote/]
I think you may be on to something there, because it looks like you have it wired right.

 

What driven gear did you use when you installed the new VSS? Make sure the driven gear and drive gear are in good shape with no missing teeth.

Do you still have the original 89 VSS? That one should also be a 4000 pulse unit. The buffer box originally converted the 4000 pulse sine wave signal down to a 2000 pulse square wave, which then went to the ECM (the TBI and MAF TPI ECMs used a 2000 pulse signal).

If you still have the 89 VSS, slide that one in the tranny and give it a try. The only thing different with it is probably the wiring connector. Make sure that the drive gear, and the driven gear are in good shape with no missing teeth.

 

I can't find the original '89 VSS. I pulled that one out because the new harness wouldn't plug into it and I didn't want to splice up a new harness, so I bought and installed a new 90-92 TPI/auto VSS.

I should have more time to spend on the bird early this coming week. I'll pull the VSS out and I will post what I find.

To all who have posted on this thread thusfar: Thanks for the continued help! I'm sure I'll need more before this issue is finally solved!

 

Deleted.....

 

I changed the pin # to D My mistake but you will probably have to move your wire to matchup.

 

I didn't use that connection terminal, I just spliced into the B11 brown wire at the ECM with a T type butt connector and then connected it to the grn/blk wire that I clipped off of the VSS buffer box.

I think the VSS is bad or has a miss matched set of VSS gears. I won't know for sure until I find time to take it out. Hopefully this weekend.....

 

Update:

Pulled the tailshaft housing off of the 700r4 to find that the vss gear was not meshing with the inner plastic gear on the tranny shaft. The clip to center the inner gear was missing and that caused the gear to be away from the vss gear by a few inches. This was the cause of the vss not spinning and not sending signal intern causing SES code 24. When the tranny was rebuilt, the shop probably lost the retainer. So... installed the inner gear retainer, reinstalled tailshaft housing and vss.... SES Code 24 went away and speedo is now working!!

Thanks again for all of your help!!