well? car is a 79. ive seen a couple 83-84-85 tachs that dont work well when cold, this one reads about double what its supposed to. is it something else maybe?

Perhaps it's not effectively switching from volts to tach?

it could be, now the question is why would it do that?

You have an aftermarket to test it with?

nope only an oem

bleh, Id say pick up a cheap one from (insert random autoparts store here) and try it out. Then take it back and get a refund once you know the results.

did you pop the hood and make sure it doesn't have a v-8? It happens.

nope factory engine

Most autoparts stores here have a return policy on electronic parts. If it's 'installed', you can't return it for a refund.



Do you have a dwell/tach meter handy? Does the car still have points? Or has someone butchered in an FB electronic dizzy?

its still got points, i put the dwell meter on it, and the dwell meter says 800rpms, engine sounds like 800 rpms, tach in the car is at 1600ish, we're thinking a diode or something went bad in the tach.

sometimes my 83 tach reads ~300 high. Kind of strange.

ok now it reads right at idle, and its mostly ok up to about 2000rpms, then it starts jumping around, i'm thinking it needs new points, or an electric distributor. engine seems to actually run fine, its just tach oddness

I had to redo the wiring on my tach for my 79, I remember the wires being awful brittle but then this car had been sun blasted really bad. Those wires were so bad it was amazing that it would work at all with the nasty voltage drop which is probably the issue.



Do the electric distributor, you'll be much much happier with the results unless you just love setting points. Engine ran a heck of a lot smoother, if that fixes it great!



The 79 tach runs off the leading coils if I remember rightly, something about the trailing not always firing because of that lovely thermal reactor, this is of course different from every other 7. Double check it even though it sounds like there's no problems there, yellow/green wire f I remember right agan it's been awhile. Clean the tach up as well, the grease mazda used wasn't the best.



So clean it up and check the leading coils. https://www.nopistons.com/forums/pub...IR#>/bigok.gif

lol, well you're right..... even the wire color

Geesh normally I do good to remember my name, why I'd remember all that correctly is beyond me https://www.nopistons.com/forums/pub...#>/biggrin.png

lol i know, cant tie your shoes, but you need to know about mazda's point ignition?

well it works now! the distributor is/was a parts house reman, and they had the points ground going to the wrong place. i put a new breaker plate and factory points, fired right up, tach works perfectly, who would have guessed?

ok good. now see if it revs to 9500 https://www.nopistons.com/forums/pub...#>/biggrin.png