VSS (Vehicle Speed Sensor) Buffer ????

[Black Car]

Here is some back ground information.
I have a Cyberdyne digital dash with an external VSS connected to the speedometer cable under the hood. The two wires from the VSS goes to the dash and then one wire from the dash goes to the factory Buick harness.

Now the problem that I believe to be the VSS buffer.

My digital speedometer work (appears) fine, the numbers appears to be stable & NOT jumping all over the place, when cruising. Comparing to my scanmaster2 the speed reads just about the same.
According to Direct Scan, my computer (after 5-7 minutes of driving time) is seeing speed jumping from actual speed based on speedometer to speeds up to 190 mph. ie. I am doing say 60 mph and the computer is seeing anywhere from 60 to 190 mph.
The speed is changes almost every frame (18.2 frames per second) according to DS. The sometimes it goes back to reading the same as the dash speed.

Has anyone had a similar problem?
I am planing on replacing the buffer, but just checking to see if anyone else has seen this situation.
Heck with my 300,000 plus miles driving a turbo Buick I have seen many unusual things.

This was causing me to have (or so I thought) a miss or engine cutting out. Actually it was the computer was shutting off the fuel because I was hitting the 160 speed limit in the chip. Upped the speed limit to 200 on my chips is working so far.

Gary

 

[Roger]

I had a similar problem with my Cyberdyne dash setup. I never had a scanmaster until after I found a fix for the problem.

I put the Cyberdyne VSS under the hood where the two sections of the speedometer come together (near the PM). I then disassembled the VSS from the original speedometer head & mounted it back on the speedometer cable & in a protective box (to prevent rhe spinning VSS from picking up a wire under the dash). The Cyberdyne VSS allows insertion in the speedometer cable & it drives the section to the original speedometer cluster.

I was then using the original VSS to feed the speed sensor buffer so the computer & the cruise control both work properly. The Cyberdyne vehicle speed indicator sometimes jumps around about 2 mph, but usually reads fine.

 

[Black Car]

Thanks Roger,
I installed my original dash back in 92-93 and this was Cyberdyne replacement that I installed in 98-99. It appearently has been working well up to about a year ago. Car has been down for the last 6 months so I didn't think about it.
I understand how you are using both VSS units and it is clever.

What I an looking for is anyone that has had any trouble with the VSS buffer which is after the VSS signal. If my presumption is correct, even doing the VSS your way I would still have the trouble if it is the buffer problem.

Gary