Please help, I am at my wits end. I did an 02 6spd LS1 swap in my 1991 Z28. I used the Speartech wiring harness, brand new custom for my car, not a mod on the original harness. Everything works, except my speedometer. I have checked everything. I called Speartech and everything looks good on their end. I even took the whole cluster apart and everything looks fine. I dont have access to any type of data logger but what are the odds the ecu is not sending out a signal? Anyhow, I disconnected the VSS to see if it set off the check engine light and it did. I know poor way to check out put, but with it disconnected it turn the light on the second I started driving.

I called the dealer to see if they could hook up to the OBD II port and check for a vss signal, they said they couldnt because I didnt change the BCM, or body control module. They also said that is probably why my speedo isnt working. I dont remember seeing any change that, so they sound like they are full of it.

What else can I check?!?

 

Did you take out the buffer box. If you have a tbi, find the brown wire and hook them together to eliminate that box. For TPI or v6 the wire is grey





the speedo wiring is like this:

http://www.austinthirdgen.org/mkport...F_and_vin8.jpg

or if you had a tbi

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

 

mine was a tbi car and the brown wire worked for me, as described above. no problems.

 

I cannot figure it out, what would happen if I looked at the pinnout for the dash and ran a jumper from right behind the dash and over to the computer and wired it into the wire for the speedo output? Would that be a safe test? I am running out of ideas. Everything checks out. What can I use to double check the output signal on the wire that puts out the signal? I know volts/ohm meter wont read it. So what will? I know the computer is outputing a signal because I have had the car data logged, but I cannot be certain the wire coming out of the computer is putting out that same signal.
Please help!!

 

Ok, I did this backwards and figured it out

Use a regular old test light. Hook it up to the speedo output wire from the pcm. Drive the car. If the PCM is sending a signal, the light will pulse......

I found this out as I had swapped the speedo and the cel wiring. As I drove, I was freaking out that the cel was flashing at me, but would stop when the car stopped..... lol

good times!

-jason

 

we are having a similer issue and were thinking its the buffer box our car in a 92 tpi z28, just haven't had a chance to see about the deal w the buffer boxbut we used an 05 gto motor tranny and ecm

 

tpi cars didn't come with a buffer box

good luck with it

-jason

 

I have an E motor car, getting an LS1 with 4L60E. So the brown wire to the cluster gets the NEW PCM's speedo output wire and it gets removed from the buffer box?

Sounds easy, I assume the ratio/speed would even be the same if the cars had the same gearing and approx tire size? OR does the New PCM flash at a different frequency?

Thanks inadvance

...Jim
W.E.D.

 

I went as far as to remove the cluster and disconnect the Speartech harness, then I checked continuity for the wire listed in the pinout for the speedo to the harness underthe dash on the passenger side. It checked out good. Could the removal of another system be making it not work? Like the cruise for instance, I removed it because my LS1 settup isnt going to control a vaccumn operated cruise. I am at a loss. For now I just leave my OBD II port scan gauge selected on mph, but I really want the speedometer to work!

 

I had the same problem and in my case the fix was to run the VSS direct from the trans output to the speedo and it started working fine. I guess the signal loses too much punch when routed through the PCM first. FWIW I have an autometer speedo but this should still do the trick for your stocker.

At first I left the VSS only hooked up to the speedo and never bothered hooking it back up to the PCM but I found out that it affects quite a few run tables so I spliced into the feed and ran a second lead to the PCM and the speedo still works fine. Mind you I didnt notice any difference at all in how the car ran either with or without the VSS connected to the PCM but its supposedly needs to be there so it is.

 

Thanks allot, I will give that a try. I guess I will need to pick up a convertor box, but that is no big deal. Thanks again, I will let you guys know if this works on my car.

 

Did you verify that the wire from the PCM is indeed sending a signal to the speedo? I don't mean verifying the wire via a chart either.

A simple test light will show you if you are receiving a signal from the PCM. Just hook up the test light up to a ground, other end on the wire and move the car around a tad bit. It'll flash if you are getting a signal.

The wire from the PCM could have broken off.... stranger things have happened.

-jason

 

Bradly I must say I am amazed at how many of your threads I have missed for some odd reason. I usually read all posts in this section within a week or two tops but this one is months old. Anyways good luck man hope it works out for ya

 

Okay I have been real busy. I am just getting back to trying to get my speedo working. I was going to try what cam suggested and go with maybe I have too much of a drop in signal by the time it reaches my speedometer. I want to run a jumper.

Would the place place to do this be in front of the firewall by steering column where I originally spliced in my Speartech harness? Or should I run a jumper straight from my vss off the tranny to the back of my cluster? Does anyone have a pin out for the factory cluster so I know which one runs to the speedometer?

Thanks in advance!

 

Use the PCM output direct to your speedo

R50 to C207 pin D (90-92 V6/TPI no buffer box) or Pin F (90-92 TBI, 86-89 Birds, buffer box must be bypassed)

Dont tap into the VSS wires. Find anyone with an OBDII scanner to see if the VSS works Autozone is fine for this. Go to live data on the scanner and move the car across the parking lot. It will show a VSS signal or lack of. If you see a speed value other than 0 then the VSS and related wiring works fine, check the output wire to speedo circuit

V6/TPI
http://www.austinthirdgen.org/mkport...F_and_vin8.jpg

TBI and older
http://www.austinthirdgen.org/mkport...SS_V8_vinE.jpg

Cluster stuff
http://www.austinthirdgen.org/mkport...uges_part5.gif
http://www.austinthirdgen.org/mkport...ter_pinout.jpg

 

I know this is an old thread, but I am having the same problem. So following what pocket posted, i just need to go from r50 to pin d on the c207? is there anything else that needs done between the c207 and where the vss plugs into on the t56? Just wanting to make sure.

Thanks,
Jay

 

For 90-92 TPI/V6's, use C207 pin D and you're done
For 90-92 TBI and all older cars with an electric speedo, use C207 pin K and bypass the buffer box

 

Double sorry for brining up an old post. I have a 1987 TA TPI. Was a 5.0. LS swapped and got a pocket modified harness. Whoot. A few years ago.

My speed not working but didnt sweat it until later. Well, later is now here. What do i gotta do?

 

Need more info on your current setup. Trans? Which LS? Which ECM ect.

 

Get a speedhut set of gauges. Didn't the cable speedo and go GPS. Mine works flawlessly and I never have to reprogram.

 

Wow. I like how I'm just now getting to this. lol.

Car is a 1987 TPI. Was. Got a 5.3 LS running off a PCM from a 2002 Silverado technically. I think its got the "red/blue" bung they call it?

Running an early model 4L60E.

i know the yellow buffer box is untouched and in the passenger side dash.