Ever since I swapped from TBI to speed density TPI, my speedo hasn't worked at all. I tried many different VSS and speedo drive/driven gears, but the speedo & mileage never moved.

After looking through my GM service manual for the '92 Camaro, I found the easy solution to the problem...TBI cars have a "VSS buffer", where the V6 and V8 mpfi cars do not. Simply put, the speedo is looking for a signal from the VSS buffer which is not hooked up to the VSS anymore (if you swapped in a TPI harness). The TPI harness sends the VSS signal directly to the ECM and then out to the speedo.

To do this, all I did was pull down the passenger side lower dash panel, remove the VSS buffer screws and let it drop down, unplug it, and find the speedo output pin (pin C, brown wire) on the unplugged connector. Then find the speedo output pin at the connector that connects the ecm harness to the instrument panel harness (black/clear dual connectors, pin D, gray wire). This connector is in the same location under the dash. Simply push in pin D/gray wire from the front of the unplugged connector and remove the pin/wire from the connector. Plug back in the dual connector...your done with it.

Take the gray wire/pin and insert it into pin C of the unplugged VSS buffer connector (brown wire at back of buffer conector). Either apply electrical tape or zip tie to hold the buffer connector to the instrument panel harness to keep the newly inserted pin from coming out. Test drive it first before you reassemble everything.

I took it for a short drive and for the first time in months, I have a working speedo!! MPH, odometer & trip meter all work! :lala:

I just thought other people may need this info as it should be a problem for all '90-'92 TBI-TPI swappers....I know at least one guy that needs this info...

 

One of those guys is me... After doing this how accurate is your speedo. I have been trying to get mine to work since my swap with no luck either. Got any wiring diagrams. Don't have my helms manuall with me untill Saturday morning and I am anxious to see the speed I am actually going.

 

I didnt know you guys were having a problem with this. My dad did the exact same thing to his speedo when he swapped his 92 RS. So why didnt you notice the speedo buffer on your wiring diagrams?

 

I haven't clocked it yet, but it feels fairly accurate. I don't see whay it wouldn't be as I have the proper gears in the trans for the 3.42 rear I have. The speedo is the stock 110mph, so it just won't read past that... ...for now, until I find a 145mph cluster!

Kevin...I really never took the time to look at the diagram until 2 different speed shops couldn't figure it out by messing with the VSS & speedo gears. I had never read any info here about the VSS buffer being an issue with a TBI-TPI swap. I wish I had known sooner as this was a very simple fix that took less than 20 minutes from tool gathering to driving the car...
It really sucked not having any idea how fast you're going or how far you've gone! For those wondering how many miles I clicked over while the speedo wasn't working, it was well under 100 miles...the car still has only 48,700 miles

 

cause we are slackers and never thought it would be this simple of a fix. I get to work on the car tomorrow and I am hoping to get mine working also. Ive got the 145 cluster and shift light stays on, will this fix delete the shift light from being lit up?

 

Would be the same thing for a firebird as a camaro???

 

I don't know about the shift light (mines an auto).

The fix should be the same for a TA...

 

My 91 doesn't have a grey wire on the dual connector and nothing is hooked up in the pin d spot

 

https://www.thirdgen.org/forums/elec...-odometer.html

this the thread i had about it, someone posted how to fix it.