I have never gotten my speedo to work on my TPI engine swap. I have a 1985 350 5.7 TPI out of a Corvette. I installed this in a 1964 GMC pickup. I upgraded to the MAP sensor with a new computer and harness for the speed density setup. ever since then, my new speedo will not work, nor can I get a reading off the computer from the vss. Since it is not seeing the VSS, the engine does not run right... I have tried a new VSS first... then checked the pin outs.... Then downloaded Datamaster and I get no signal from the VSS... Can anyone give me anything to check .... I am about to dump this whole thing, and put a carb on it..... It sucks!

Not exactly thirdgen related. The electronic speedo from a thirdgen has a VSS mounted on the tail shaft of the trans. A cable-driven speedo has the VSS mounted on the rear of the cluster.

JamesC

I've put 4 TPI engine/trans combos in a 67 bird, 37 Chevy, 40 Chevy, and 35 Plymouth, and I've used the speedo plug from 92 Camaro and Caprice police car.
It has speedo out gear and VSS output also. The cop cars used the cable output to sync their radar units.
My friend at an O'Reilly store says he can get them no problem in the 50.00 range in good aftermarket brand.
I bought a half dozen units about 8 years ago from AC Delco dealer. Delco part # 213-201, GM # 10456131.

Sorry, I didn't mention I also have the 700R4 that came with the vette also....


** Edited ** Sorry, just frustrated with the whole thing

I know that there is a difference in the TPI VSS unit and the TBI unit.
I believe the TPI takes a 4000 pulse and TBI is 2000.
The Cop car Camaros had the TPI, so you can use it.
There was a DRAC unit also that was mounted in car for speedo conversion, but the streetrod speedos mostly are electric now, and come with a gear drive convertor. I'm almost sure that it will not drive the VSS signal needed
Someone can correct me if I'm wrong.
There's always someone here that can answer most questions.
Guys on here have saved me several times.
Ron

OK, let me see if I can be more clear....

I bought a 1985 Corvette Engine and 700R4 Transmission....
I bought an upgraded engine harness and computer from Chevythunder
It is upgraded to the speed Density MAp version for the 90-92 firebird
I have a 4000 pulse VSS

I have swapped out the VSS twice in the tailpeice, but when I hook my laptop up, the computer is not getting a signal from the VSS.

I have the right driven/drive gear combination.

I have brand new electronic Dolphin gauges...
Everything else works...

Thanks for helping

Chad

So using the later (S-D) ECM and 4K VSS isn't working? The later ECM doesn't require the buffer. The two leads from the VSS (purple and yellow) should connect directly to the ECM on B9 and B10, respectively.

If you disconnect the VSS from the harness and read AC voltage at the VSS directly, is there any signal?

so are you saying unplug the VSS harness plug and read voltage between the 2 leads on the harness plug?

Do I need to crank the engine or will there be voltage there with just the switch in the on position?

OK, I unhooked the harness plug from the VSS.

I started the engine.

I read about 18 mV A/C.

So does this mean for some reason the ECM is not sending enough voltage?

Does it always send 12 V to the sensor?