The VSS drives a module in the dash cluster, which buffers (smooths) the signal and send it to the speedometer, the cruise, service reminder module, and the ECU. Might not see the speedometer fluctuate. Don't know how much buffering is on the line going to the ECU, but with a scanner it may show some speed variation. Getting it to repeat while you are driving in traffic on Ga 400 with one eyeball on the scanner might not be a good idea. This is a pix of the dash module.

 

When my VSS went out the variations were clearly visible on the scanner, while absent on the dash speedometer.

 

Yep, just as I feared. That would mean the ECU detects high speed operation in a few milliseconds, and pays no attention to the fact that 100 milliseconds ago you were going 65mph.

 

I'd try swapping the TPS first (cheapest and easiest DIY fix).

 

Hello everyone, i had the same problem on my 96 disco 7, no CEL, now what i found that helped my problem was a little plastic filter that is located in the rear of the fuel tank neck,underneath the truck.(crawl under the and look at the neck, you will see the white little filter). I removed it and it was completely clogged with dirt and other stuff, making my fuel tank air tight thus making the fuel pump work extra pushing the fuel out. i took it out and no more hesitation. hope this help.

youll be surprised the little things that can make a car fail

 

BTW, there is a great rebuild solution from gprtech yesterday that I may just try. It looks fairly simple

 

You may not see anything on the speedo. However, if the VSS is the problem, the ECU should have freeze frame data showing a vehicle speed at 117mph or above. Unless you've actually gotten up to that speed, that's the VSS flaking out. When the ECU sees that, it cuts out every other cylinder to reduce speed.

Why anyone thought that was a good idea is beyond me.

 

Nice catch on the freeze frame. How long is that stored? I agree there is not much point, the take off velocity for a brick is much higher.

 

Unfortunately, I have no idea how long the freeze frame is stored. I got the information from one of the TSBs.

Dsmeddy, if you try it, I'd appreciate feedback. What looks easy to me doesn't always work for someone else.

 

gprtech posted a very accurate rebuild for the VSS. I just did mine in under 2 hours. 1 hour just getting the dern thing back into the vehicle. What a bugger. As my issue was very intermittent, I just went up and down the highway up to 80 mph and no issues. Once I opened the thing the inside was full of smudge and stuff. Cost me all of under $30 to buy everything needed, including the gauge.