I already posted this in the V6 section, but I'm not sure if that was the right spot:

Alright... I need some help, I'm clueless at this point Here's the deal:

For a long time now, my speedometer has been bouncing around. 6 months ago, it would occasionally just lag at 0 for awhile before jumping up to the right speed. A couple months later, it still did that, and also started 'ticking' down a little every ocuple of seconds, so like bouncing... Now, things are far worse, it rarely ever even indicates a speed, and when it does, it just continuously bounces to the point that I have no idea what speed i'm going. Also, the Trip/Odometer don't count up when its stuck at 0 (so this makes me think its not the meter itself thats broken, but the signal going to it, since all 3 functions exhibit similar performance.)

I like trying to figure out how things work, and I don't like askin for help unless I need it, so this is what I've tried. My dad mentioned something about a loose speedometer cable... after attempting to remove mine to check, I realized that i don't have one (I don't think) My entire instrument cluster is electronic, the only connections into it is a little socket behind the cluster. So after more research, the cable is only on manual transmissions I think... So anyways, I'm ptretty sure I have a 'speed sensor' and its all just wires between... is that right? And if so, how does the speed sensor work? could it fail intermittently like this? Also, I looked at how much a new speed sensor would cost, and there's like 8 or 9 different options... I have no idea which one I need.

So, what I'm asking is... could the speed sensor be the problem? Is it likely the problem? And if so, where is it located, and how do I get it out? And one last thing, the socket/connections are pretty nastily gunked up, could that be causing it? Its only 3 of the pins, and it doesn't look bad enough to limit any current flow.

Thanks!

 

New question, can someone just give me a quick lesson on how my speedometer works exactly? What turns what to generate the signal that is sent to the speedometer? I think if I knew this I could diagnose this problem pretty easily... maybe Thanks.

 

https://www.thirdgen.org/forums/elec...king-help.html

Found this today, anyone having the same problem, the entire system is explained in that post.

 

The only real difference between that post and your setup is the VSS buffering. In the '90-'92 port injected modeals (TPI & MPFI) the ECM buffers the VSS signal. Only the TBI models still use the yellow buffer box (4-OUT BUFFER).

In the ECM buffered models, the VSS signal (2 wires, twisted) go to the ECM. The ECM converts the AC pulses to DC and sends them to the cruise control and speedometer.

RBob.