My tach just stays at 2500rpm when the engine is running. Took it out and cleaned the 3 pins connecting it no help. Where is the signal comming from that feeds the info to the tach? Is there like a sending unit? Is there any way to bench test the tach?
Thanks

 

This is a good question. Mine has been stuck at 4 grand since the day I got it. Whether its on or off, the tach says 4 grand.

I am not sure about a sending unit or anything like that. My book contains no wiring diagram pertaining to the guages. I havent really had time to pull it apart and see what is going on with it. Aftermarket tachs have a lead that hooks up to the neg. side of the coil, a battery connection, a ground, and a wire to tie in the illumination with the interior lights.

I would imagine the factory tach would get its signal from the computer. This is just my guess, not hard data. I may be wrong on this, if so please correct me. But I would think that the computer would be able to tell the tach what to display since it knows via the crank sensor.

Hope this helps and I havent led you astray.

 

On my '96, the tachometer is controled, basically, by a "tachometer module" that is mounted right above all the gauges (if you pull out the instrument panel assemly, you can see it). I have no idea when they changed to this setup.

If you read the first paragraph, it says if your tach does not return to 0 after you turn the ignition to OFF, to check for battery voltage at the fused B+ cavity of the left instrument cluster connector (red connector, cavity H).

The frequency chart is as follows:
2000RPM (+/-140) 66.7Hz
5000RPM (+/-140) 166.7Hz

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