Ok, I did a search and couldn't find a definitive answer. Hopefully someone smarter than me can help out...shouldn't be hard as I know little about electronics. I need help with compatibility of these 3 items together.

I am swapping from a cable-driven OEM speedo to an Autometer elec speedo. I know the OEM speedo had the optical VSS which sent the ecm the needed signal. I also know my '165 ECM uses a 2000 pulse square wave signal. I will be using a chip for the 89 with the VATS removed.

The tranny I'm using is the Aftermarket T56 which uses the speedo hookup for a T5. I have 2 differant VSS units I can use. I have the cable type unit which I can use that uses the *pass thru* VSS which is a 2 wire unit. I won't be using a speedo cable anymore since I'm converting to an elec speedo. I also have the elec T5 unit which only has an elec connector on the end.

My understanding is the 2 wire VSS I have (from Howell-EFI.com #VSS263) is a 2000 pulse unit. Both wires coming out of it are white and there are no identifiers as to which wire is which. The elec one I have is like the #55X on here http://www.transmissioncenter.net/sp...__va.htm#Cable I know it is a 4000 pulse sine-wave signal. It has no speedo cable provision.

The engine is a freshly rebuilt modified engine and I'll be getting a starter chip from PCMforless anyway.

Now for the questions:

1) Can I use the elec VSS without the speedo cable provision with the 89 ECM/Chip? Can the chip be modified to use either/both 2000/4000 signals?

2) Can the pass-thru type VSS be used without damage with no speedo cable hooked on the other end?

3) How do I tell which wire on the pass-thru unit are high/lo or signal/ground? Does it really matter?

4) Should I run the VSS wire to the speedo and then to the ECM, from the ECM to the speedo, or a seperate with from the VSS to each (one wire to speedo and another to ECM)? I read somewhere (lost info ) about a buffered signal and unbuffered signal and what is needed for the speedo and ECM.

5) How can I get this all wired to run correctly?

6) If I can use the elec VSS (which is the one I can hopefully use - cleaner setup) what has to be done to the ECM/chip to recognize the 4000 pulse signal when the 89 TPI ecm uses a 2000 pulse?

Please help me get this wired up correctly the first time so I don't fry anything that I probably can't replace (finiancially) right now. This car came with no speedo in it and the previous owner was going to put in the new elec speedo but never got it installed. I need to get this wired up and running.

Many thanks to anyone who can help me out. Nobody locally has any idea how to wire this up. I know the knowledge is here.

 

I am not aware of being able to change the required pulse on the chip
I recall in one setup ,the VSS signal up goes to ECM , then speedo and the other goes the other way around
Best to ask over here
https://www.thirdgen.org/forums/dfi-ecm/

 

After doing some other snooping around on various websites, I think I've found a way to run the 4000 pulse elec VSS and still get the 2000 pulse signal the ecm needs. The speedo can use either as far as I can tell.

If I run a 4 output VSS buffer the 4000 pulse sine wave signal goes into it and then it splits the signal into 2 outputs which are 2000 pulse square wave.

Can someone confirm if this is correct? If it is what I need, which salvage yard vechicles would have this?

Thanks

 

You are correct. Most 86-92 firebirds have them as well as most LO5 trucks

It looks like this and can be yellow or white


http://www.austinthirdgen.org/mkport...SS_V8_vinE.jpg

Use the 4000PPM VSS, the buffer will split the signal to 2000PPM your ECM/cruise need and 4000PPM your speedo needs

 

If it is like the elec speedo we put in a buddies car , it will input anything up to 16,000 pulses.
You calbrate it by running a measured mile

 

Cool, thanks Pocket for that info! I was reading some other post after my search and after I posted this question. I believe it was one of your post that got my mind swirling and came to this solution. THANK YOU!

Vetteoz - Yes, that is how my Autometer is programed. It makes no mention as to which is better (2000 or 4000) but you drive I believe 1 or 2 miles.

If anyone has this buffer WITH the plugs, please PM me with cost. I also need the pigtail that plugs into the VSS but I can get that seperately if necessary.

Doug