Tony Trans Am

Hi,
Just got my 1990 Back from the shop and noticed the speedo is not registering unless I'm going fast. It stays at 0 at town speeds. Could they have knocked something fitting the new injectors.

Cliff Harris

If you have a C68 HVAC system you can check your speed on the HVAC controller. There's a video on YouTube on how to do this:


The vehicle speed goes from the VSS in the trans to the PCM and then to the dash. You want to determine if it's getting lost before or after the PCM. That will narrow things down and make it easier to find the problem.

WVZR-1

I'd think it more coincidental than anything that they created. First of all if the speedometer LCD works the speed of the car should have NO effect. I'd first check the VSS electrical connector at the transmission. It isn't unusual for that connector/connection to get flaky. On a '90 it's a very straight forward weather-pack shell that you can buy service terminals at most every auto parts store or fleet vehicle dealer. I'd do nothing else first.

A bad VSS? Maybe. Do you have a FSM? At the ECM the VSS is pinned to G2 (yellow) and G8 (purple). You maybe want to be concerned with the "purple" at the VSS and ECM. I assumed your car is an L98 and NOT a ZR-1/LT5.

Does your cruise control work at both high and low speeds?

Churchkey

My 90 decided to stick @ 46mph. I have a short fuse sooooo a few smacks on the top of the dash with a closed fist brought it back to life. The next time the cluster was removed I cleaned the printed circuit & plug in connector = no more issues.

Tony Trans Am

Driving my 90 vette around today and the speedo started to work perfectly until I got back to London, It of felt as if the over drive couldn't make it's mind up whether it was in or out. What RPM should it turning at 70mph.

Tony Trans Am

Driving my L98 90 vette around today and the speedo started to work perfectly until I got back to London, It felt as if the over drive couldn't make it's mind up whether it was in or out. What RPM should it turning at 70mph. In regards to speedo how can it work perfectly then not, surely it's the speed sensor as the dash would either work or not work.


What's a FSM? What's an ECM? I am from the U.K.

WVZR-1

FSM - Factory Service Manual

ECM - Engine Control Module (black box up near the booster)

G2 and G8 are the pins at the ECM where the VSS wires connect. Check the wires yellow and purple at the VSS connector, confirm connection and move on. You hadn't mentioned UK before so sourcing your needs could be interesting. There are a couple very good resellers there though. Put your location in your profile and maybe another UK guy will respond.

Tony Trans Am

Thanks I'll look tomorrow, which plug are they attached to? If you were sitting in the car, Left, right, middle?

WVZR-1

Pin outs vary depending on the source. FSM G2 & G8 (ECM connector is GREEN) Some note the connector is C (A, B, C & D used to ID connector) so it's displayed C2 & C8.

Here's an ECM pin-out chart for L98, page down to '90 & '91:

http://chevythunder.com/fuel%20injec...ts.htm#1990-91 speed density (Corvette ecm #1227727)

In this one page down to L98 '90 & '91:

https://wiki.bentleypublishers.com/p...ageId=17989640

The VSS is drivers side rear of the transmission. On a '90 it's either black or white in color 2 1/2" in diameter with the yellow/purple connector in the center.

Tony Trans Am

Does anyone have a definitive picture of the VSS.
Whilst trying to remove mine today it all fell apart springs the lot! I'm not sure if there is a piece still in the transmission. How is it fitted in there, twists etc. I tried levering it out hence it went ping!
Where can I get a new one? super pissed off!

WVZR-1

Is yours white or black? Count the number of teeth on the gear to confirm it's correct. Was your speedo/odo correct before?

Tony Trans Am

Black. No teeth the wheel is still in there!
Do you have a pic of yours pulled?
How do you pull it out?

WVZR-1

Just "GOOGLE" 25007308 and you'll find many different images. If you've demolished the VSS retaining ring and the black center aspect then you need and the black is quite expensive. Not available as new any longer and used gets expensive also. I might have a black/correct NOS but it would be expensive.

There will of course be some "incorrect" images BUT I can assure you that the image I borrowed is correct and you should recognize it as what you demolished. You apparently tried prying on the sleeve that is used as a retainer around the circumference of the VSS. You need to pull straight out and you can wiggle/twist some to help.

Tony Trans Am

Just my luck! Ok how much is your one and please don't beat me up too bad!

Tony Trans Am

What's the difference between 25007224 VSS and 25007308 VSS? both say they fit a 90 Vette.
Mine is an L98 Auto.

WVZR-1

'7224 is White and the '7308 is Black, black is for 40+ tooth count and white is for 39 and less.

Your 2 tooth count and the black VSS indicates that your '90 should be a 3.07 rear axle ratio. G44 on the SPID label that should be attached to the back-side of the console door.

I've received your emails and I'll be back to you.