I have a 1991 firebird with a 3.1 v6. Recently my speedometer has been going crazy and bouncing all over the place and then it just stopped working. When it sits on 0 car runs fine but when the Speedo starts bouncing you can feel the car bog down everytime any ideas on what will fix it?

 

Thats really odd. Because the speedometer circuit has almost nothing to do with driveability. If I were to throw a shot in the dark though. Get your battery and alternator checked for free at advance auto parts. If either of those are failing it could impact driveability and the low voltage could cause your gauges to bounce around.

Check for belt slipping or a seized pulley. Imo.

Otherwise can I get some more info?

Only when hot? Cold? All the time?
Only at idle?
Under heavy load? (flooring it)
Light load? (cruising on the freeway)


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If it stopped working I would look at your vss on the transmission


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Well it does it at random. It bogs on a normal basis but seems worse when Speedo is bouncing. What all reasons would it bog so much in first place?

 

Ignoring your speedo completely. Your iat , cts, map, iac , icm , and the entire fuel system. Could be any of those. I would start by checking fuel pressure.


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Locate the diagnostic connector (ALDL) located by the fuse panel under the dash. You will want to put a wire in it in the terminals in the upper right hand corner. The SES light will flash in a sequence, or it should.

If nothing happens with the SES light and the wire is in the ALDL correctly, that is one issue. If the SES light isn't on, period, that's another.

One of the sequences you will want to be on the watch for is a 2-4 sequence, which is the trouble code for the VSS in the transmission.

And yes, the VSS does have effects on driveability. There are separate fuel and spark maps for "highway mode", and the ECM doesn't know to go into this mode without a VSS input (which is why the VSS is connected to the ECM).

 

As true as that is. I drove without a vss for 3 months with no problems when I bought my car.

I figured it wouldn't be that.


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Well I recently replaced fuel pump, sending unit, filter, and distributor, has new plugs and wires, I'll check the vss this weekend if I have time.