Speed sensor issues after diff swap

[Rugbyfan]

I recently went from a 3.25lsd to a 3.46lsd in my '87 obd-1 swap. Previously there were no codes thrown. Now every now and then I'll throw code 2a-vehicle speed sensor not present. This code only popped up like once every two weeks. I have now realised that it only appears after driving >65mph or so. When I swapped diffs I did not swap speed sensors, and since my speedo worked I assumed they were both good. So the question: is there a different speed sensor that I need? I though all e28/e30's were interchangeable.

[Rugbyfan]

Bump, can a sensor fail at higher speeds but be ok at lower speeds?

[Rugbyfan]

Ok if I don't go high speeds code 2a won't come up. If I go on the highway and get it to trip I then hit a fuel cut (every gear) of around 6300 rpm. To the wiring guru's how often Do diff sensors fail? I just replaced my speedo, could it be giving a bad signal to the DME? Within the last year Dave made some sense of my hack wiring harness so I doubt that the wiring is the culprit. The speedo works fine, as does the econometer. Thoughts?

[328ijunkie]

If you just replaced your speedo it may be giving the ECU a crap signal thus triggering the code. The VSS is output from the speedo and ive seen them crap out and output a bad signal before.

[Rugbyfan]

Since the new speedo never twitches and always reads accurate would you estimate that everything "upstream" of the speedo is probably ok? That's what leaded me to think it was an output issue too. Thanks, I was hoping you'd chime in.

[nando]

the output to the speedometer's needle, the output do the odometer motor, and the VSS output from the speedo are all seperate signals. Basically, just because the needle and odometer work doesn't mean the VSS out is working right.