Tach nervous breakdown

[njspider]

1982 Spider. My tach goes wonky. It will seem okay and then zooms all over the place. Is there a way to test if it's the tach itself or some other cause?

[spider2081]

I think the 1982 Spider fuel injection and tachometer share a connection on the ignition coil. Have you checked the brown/white wires connection on the coil? If the engine's performance seems proper when the tachometer is acting up it kind of points to the tachometer or the connections for the tachometer.
The ignition control modules have been known to cause erratic tachometer operation but I would think some engine performance would be noted if that is the case.

[njspider]

Thanks for your reply. The car is running great and I did check the connections on the coil so I'll start looking for a replacement tach. If anyone reading this post has a known working tach, let me know. Thanks

[18Fiatsandcounting]

Was the tach ever changed? The reason I ask is that I vaguely recall a discussion somewhere about how the tachometers were different between the points ignition and the electronic ignition, and swapping them could lead to erratic tach behavior. I also vaguely recall that the fix involved inserting a resistor in the tach pickup wire, but don't hold me to that.

-Bryan

[18Fiatsandcounting]

I also came across this: https://www.youtube.com/watch?v=-6j3glUtecY

So check all grounds, make sure the tach signal wire isn't too close to high voltage wires, and try the 10K resistor fix.

-Bryan

[rridge]

An irregular tach signal on a car with Marelli electronic ignition is often an early sign that the two fine wires that connect the pickup on the advance plate to the distributor harness are failing due to damaged or worn insulation. The wires must flex constantly as the advance plate moves. With age and heat, the insulation begins to crack. The insulation can also be damaged by careless installation of the distributor cap when the wire is caught and pinched under the edge of the cap.