But I am standing still....get it, it could have been a joke that I was going that fast? hahaha, ok I will sit down. I have a 1986 AM6 2.8 4 speed muncie. 120 mph speedo. Car sat for decade, but in gorgeous condition, no evidence of molestation or modification or even a single crispy connector anywhere on the engine. Runs and drives great, not a rattle.

I researched this here, and not sure what all the old research really says after I am done with what I saw. I have a working odometer and trip odometer, but the speedo needle does not even twitch. I removed the lower connector, gently cleaned all connections and reinstalled with no avail.

Lots of the historic advice is to "replace speedo". Ok, that would be fine, but who sells them? I do not need nor want a whole cluster when I know how to fix 1990's GM cars and trucks; you can replace the little motors, but what about Fieros? I could not find anything specific! Y'alls advice has and is great! Thanks for the patience.

FYI I may post another quirky question separately soon if I cannot find the answer. Only going to do that to keep threads separate for completely unrelated issues.

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[This message has been edited by tshark (edited 09-08-2018).]

I will try that tomorrow and report back.

There are two coils that control the speedo needle movement. One is sine and one is cosine. Sounds like one is not making connection anymore. Take it apart and clean the connections between the gauge movement and the board with contact cleaner, reassemble and test. If still no go, one of the windings or the driver chip may have failed.

Concur with above, and you can use an ohmmeter to verify that each coil is actually connected.

quote Originally posted by phonedawgz: There are two coils that control the speedo needle movement. One is sine and one is cosine. Sounds like one is not making connection anymore. Take it apart and clean the connections between the gauge movement and the board with contact cleaner, reassemble and test. If still no go, one of the windings or the driver chip may have failed.

Could be...
Speedo has capacitors the can die causing a died speedo or read off to way off depending what is bad.
Bad Solder joints can crank open w/ same result. Look at board w/ magnifying help to find cranks. Look for any joint that not like the others.

Speedo "meter motor" is bolted to board. Loosen the tighten a few time to scrub the nuts etc. If needed remove nuts, rub them w/ fine sand paper a bit then retighten. Finger tight only. Can break the board etc torquing then down too tight.

does trip/odo work? If not could be VSS or wires to it. VSS can be check w/ ACV meter and car on jack so you can rotate a tire. Any AC V then VSS is likely good.
ECM data stream reads MPH or not? If does then then VSS and buffer on speedo is OK. No VSS then ECM sets DTC 24 but sets this at random times and may not set for a short trips.
Check Those Q will narrow down the problem.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

OK, long day of working on the Fiero. The speedo...pulled out and cleaned connector connections and reset the needle to zero. When I drive, the speedo works, but it is about half the speed I am going. It does go back to zero when I stop.

Ogre, did not see your message while I had the thing out.

Half the speed may just be a capacitor thing.
The circuit is a two part circuit.. frequency to voltage, and voltage to sin/cos meter signal.
Also, the VSS frequency is divided by 2 and sent to the Cruise/ECM.
If the capacitors are leaky, they can mess with the voltages and thus you get the wrong values.
Just curious, can you put some miles on the highway, and see if your odometer is even in the ballpark?
And check the VSS?
By all means, though, try to uncover bad connections like Ogre says. Solder joints can have tiny cracks in them, and the green copper traces can also have breaks in them. Use magnification, the cracks are tiny.
The copper pads where the hex nuts torque down can also begin to chew through to the board too, making open circuits. In that case, try a washer to conduct in more than just the one ring area.

You are in a different space-time world, and you are actually traveling 120 mph, while we are all sitting still.

I had the same issue after replacing my cluster, either with the tach or the speedo (can't remember). In my case, removing the cluster, rotating it to use gravity to get the needle to rest at 0 instead was the fix. I guess gravity kept it stuck over there and I just needed to get it back to it's proper resting location.

Edit: should have read the whole thread to see you've done this already! Carry on

[This message has been edited by Leukay (edited 11-06-2017).]