I have a 1982 RX7. The tachometer most of the time works fine. But it will intermittantly become erratic and bounce around 500 rpm when it reads around 1200 rpm. At no other place on the tach does it become erratic. It only becomes erratic at about 1200 RPM. I recently swapped out the instrument cluster and both instrument clusters had the same problem so I am assuming that the tach itself is ok.

Since I don't really know much on how the tach works on first gen RX7's I am asking if anyone has seen this problem before and what might be causing it.

Thanks
Joe

 

tach's signal is from the ignitor (trailing i think) perhaps signs of an impending ignitor doom?

 

I've never had an ignitor go somewhat bad. It's either working fine or pooched in my experience. More likely the tach wire on the negative coil is loose/corroded. Check and clean your connections.

 

I have had jumpy tachs caused by crappy plug wires. Usually noticeable only under load or when there's a lot of moisture in the air. May or may not be accompaned by misfiring.

 

What color is the wire that goes from the ignitor to the tach. Where is the negative coil on the ignitor located excatly? For that matter where is the ignitor located? Sorry for the newbie question but I don't know very much about the workings of the car yet.

 

i have 2gendfi....
and my tach bounces like crazy tryin to start

the ignitors are locatedon the distrib where steel meets plastic. one facing the radiator is leading. and one facing the alt which is trailing
ya can test then with an ohm meter opps spelling and by the manual there surposed to be 1200 if you get nothin there stuffed and if there way over there stuffed i think someone correct me

im gonna re test mine today cause i cant start either

 

have you checked teh coil? do a sparkplug test.