Lazy Tach

[ThunderChicken]

replaced the SI board batteries (which was a little harder than advertised)
and my speedo is good now.

Tach still reads 1 out 3 rpms............

the guy at the junkyard says if it were the reference sensor, the car wouldn't run at all, because the computer uses that info to know when to send the spark.

so............the fault must be between the computer and the instrument cluster.
But what would cause the tach to continue to work, but in a highly inaccurate manner?

I'm gonna dig it out again and look over it, but I'd like to avoid testing every capacitor and resistor in the entire board if I can.

Any ideas?!?

 

[echothreezero]

Check all of the connectors in case one is loose.

Otherwise...

Fault in the cluster. not helpful I know, but if changing the batteries doen't work then its probably time for a new cluster.

BTW, the guy at the junkyard is correct. Sensor should be fine if car runs.

 

[E30m42cab]

new cluster, or just try swapping a different tach in... very easy to do.