Alright I've had a bouncing tach problem since I got the car, but this is not ordinary so bear with me.

1980 rx-7, bone stock for now.

The tach will bounce between 1000 and 1500 rpm, but only under certain circumstances.

The tach will always work when the gear shifter is in the 4th or 5th gear position. I can have the clutch engaged or not, free reving or on the highway, the tach will work like a dream in 4th and 5th.

The tach will always work when the throttle is completely closed. As soon as I touch the throttle below 3000 rpm in 1st - 3rd, it will go right back to bouncing. Let off the throttle again, and shoots right back up to normal.

Here is the funny part, If I let off the throttle and then get back on the throttle above 3000 rpm, the tach will work fine. This is only above 3000 rpm, as soon as the rpm drops below 3000, it will start bouncing again.

So when I am racing somebody ro doing some spiritid driving , the tach will usually work the whole time considering I shift/launch above 3000 rpm. Only a problem when cruising at low speeds, the damn thing is noisy. Tic tic tic tic tic tic....

Here are my questions:

1. Is there a switch in 4th or 5th that has anything to do with ignition or the tachometer?
2. What happens at 3000 rpm with the ignition or tachometer?
3. What the hell is wrong with the damn thing.

I have asked before but only recently discovered all symptoms of my crazy tach. Any help appreciated.

-Marques

 

Someone here will know. The 79-80 cars had a thing where the trailing ignition was cut under certain circumstances as part of the emissions controls.
I don't know what circumstances these were, but it would seem to me that a solenoid on the rats nest may be responsible for your dancing tach.

My guess is that if your car were a later year, the tach would be bouncing always. (Or not at all.)


Peejay is quite knowledgeable about these things. But a search on this may yeild alot for you to read.

 

Isn't there a way to disable the intermitant ignition on the SA's? Jumper some wire or another, I'll look around for that.

-Marques

 

Hmm I just remembered the tach runs off the leading ignition on the SA's, so I don't thing it is the trailing ignition cut.

I would still like to know about disabling the trailing ignition cut though if anybody could enlighten me.

-Marques

 

I still think it has something to do with the trailing. I'm kinda guessing arcing or interference from the trailing to the leading.

My 85 coils used to arc before I got better boots for them. The arcing is high voltage, and the voltage needed to register the tach is super low.

start it at night with the hood open. See if there's arcing going on. Meanwhile, make sure all the wiring is seperated and not laying on each other, ect.

Clean the contact tabs and nuts on the coils, **** like that.

 

Well no arcing, i've checked that before. I just bought a new dizzy from an 83 so maybe when i put that on it will solve my problem.

-Marques