911 Help! I'm doing a TBI to TPI conversion on my 1991 RS 5L. The only thing left to do is the vehicle speed sensor. If anyone out there is driving a 90-92 5L TPI, 4 speed automatic, Z28, I would greatly appreciate the RPO codes from sticker in the glove box or door jam or spare tire well. As the 5L TPI was not offered as an RS, I need the Z28 info. Confused? With this info I can purchase the correct vss and gear for the transmission and keep the TPI ECM happy not to mention the speedo and cruise control. Thanks

 

Unless you're putting the rear end from that Z28 in your RS as well, and assuming your RS is an automatic, there's no change in the VSS gears needed.

The only time you need new speedo gears is if you change the overall tire diameter, or change the gear ratio.

 

Thanks, JZA. Do you know how to make the TBI VSS buuffer work with the TPI ECM?

 

It should already work fine. You only really run into problems when you're working with a cable driven speedo ECM into an electric speedo vehicle or vice versa, and even then it's just a simple fix in the chip. TBI = 2000ppm TPI = 4000ppm IIRC...

 

Ok, let me ask it another way. Along with the TPI parts, I purchased a 730 ECM. I know from resaerch that the 730 is looking for a permanent magnet generator (pmg) vss input of 4000ppm. In 1991 did GM use pmg vss on all Camaros and add the buffer for the older TBI ECM that is looking for an electro mechanical input? If this is the case I should be able to use the existing vss and wire it directly to the 730 ECM. Thanks in advance. This last piece of the TPI conversion puzzle is all that's left!

 

I believe that to be the case, although it's been a while since I did that research.

I sort of went through the same situation, only with some added twists. I'm swapping my 89 TBI out for a '730 setup, but I'm keeping the mechanical speedo and I use an 8000ppm sender. Yeah funnage.

 

Actually, to be a little more specific, I kept the mechanical VSS (which is 2000ppm) and use an aftermarket speedometer that can adjust the number of pulses received in a mile as output by a seperate 8000ppm sender.

In my case, there's a flag in the chip that can be toggled to switch between the two VSS types.