Where is it hooked up on engine? I heard something come loose while driving and hitting a bump. It stopped working and fluctuates severely. I cant fing anything on the hanes manual, only speedometer cable!

 

I believe the tach routes to the ECU then to the trailing coil. check your connections.

 

well at least it wasn't your speedo cable haha. mine came off, hopefully my buddie when doing my tranny service is gona put it back in for me. i'd rather go with out a tach then a speedo anyday.

 

Man, when my mechanic did my clutch, he broke my speedometer cable. I havent had it in two years. I was using my tach, but lost that too! He broke the gear inside the tranny that hooks up to the speedo cable. So the tach is electrical?

 

yeah usally there connected to a coil pack on a normal car, i couldn't tell you witch it is on a rx7 its either the leading or trailing but **** if i would know which one. um lucky for me my speedo cable just came undone and i dragged the outside of the bolt for like a block when i heard the noise and i zip tied it to my frame. haha i'm a lil to big to get under my car and don't have jacks to lift it. :P

 

The tach is connected to the trailing coil. Unless I am mistaken, the ecu gets all the signal it needs from the CAS, it actually tells the trailing coils when to fire (eliminating the necessity for a tachometer input to the ECU.) I would guess that a resistor or capacitor came off inside the instrument cluster, and that is why the tach is jumping.

The FSM has schematics for the tach wiring.

http://www.teamfc3s.org/main/factory...NG_DIAGRAM.pdf

look at page 37 (50-40)

Seriously, take the cluster out and look for bad solder joints on the resistors and capacitors on the little circuit board on the back of the tach.

If you have a friend with a functional tach who is willing to let you borrow his instrument cluster, swap it real quick and see if that fixes it.

 

not tryin to flame you or anything but if you arent too worried about getting it fixed then you should be able to drive without it.....you know feel and sound, thats what i do, most of the time i dont even look at my tach unless there's a cop near by

 

The tach def does not send a timing signal back to the trailing coils. the CAS signal goes to the ECU, which then sends out leading spark timing, trailing spark timing, and trailing spark switch signals. The tach signal seems to come directly from the trailing coil

 

I think my post was unclear, that is what I was trying to say.