speedometer help

[tucsonsean]

I was all ready to (finally) take my 85 2m4 through emissions--and the speedometer stopped working. I searched thru the archives, but didn't find an answer. Here's what I checked so far:

-radio fuse is good
-wiring is intact
-no code 24 from ecm (I guess it thinks it's working ok)
-new red gear is in place on bottom of VSS
-connector under dash pod is intact

Since I'm getting no error code from the ecm, I'm assuming it is getting pulses from the VSS. Could it be the guage itself that's gone bad? Symptoms prior to dying: shaking needle, intermittant working and not working on same drive, then nothing.

Help?

 

[tucsonsean]

re-read Oreif's response to Fireogirl7's thread. I'll pull the back of the gauge cluster tomorrow. Any other suggestions between now and then would be appreciated. Thanks.

 

[tucsonsean]

Additional info re: problem with speedometer:

In addition to what I listed above, I now get a code 24 when I check the ECM. Also, I measured resistance on the VSS unit with a multimeter and it registered 470 ohms. I read somewhere on the site that it should read between 190 and 250.

Bad VSS?

It's a bigger deal than it seems because the speedometer malfunction triggers an error code, and lights up the check engine light. They won't do emissions if the light is on, and, in Pima County, AZ, you can't get registration or tags without passing emissions.

 

[bird59]

You can check the VSS with an A/C voltmeter and a drill. Pull the VSS, chuck it into the drill, spin it and read the ac voltage. If it has an output, it's working. the frequency changes with speed and that's what the ecm uses to send a signal to the speedometer.

______________________________

 

[tucsonsean]

Still fighting my speedo. I've tried two different clusters, in addition to the other things I mentioned, with no luck. I'm going to try the drill test. I understand that if I get no response from the speedo, it's possible the VSS isn't sending a signal, or the buffer isn't working in the speedo. My grounds are good, I have continuity in the purple and yellow wires, VSS to connector, and I get 12v at the speedo dash connector from the radio fuse. I think it might be a bad weathertite connector atop the VSS (the secondary lock has been long gone).

If I use the drill, where do I probe with my multimeter to isolate which part of the system may be malfunctioning?

 

[bird59]

directly on the two pins inside the connector. A helper is really handy here, holding the VSS, the drill and probing the pins of a moving connector... or use small alligator clips to the pins. Mine was showing about 175-180 Hz in my cordless drill. As I recall, voltage was around 7.5

 

[tucsonsean]

Thanks, bird. Maybe tomorrow--it actually is raining tonight here in the desert.