Currently on my SA when you go and start the car the tachometer keeps functioning as a volt meter. what would cause this to happen? also when i roll over the car (to start it) the tach needle stops working as a volt meter and bounces as it always does. anyone have any ideas?

 

Check your trailing ignitor. This is usually caused by them failing.

 

where is the trailing ignitor located. ive searched but i cant find seen to locate it

 

Tach signal is taken from the LEADing coil/ignitor on an SA (FBs do it from trailing)... it connects via a single lead on a large spade connector.

Let me see if I have a pic handy.

See yellow arrow, top center:

 

so wait. Sa's dont have ignitors, as they have ignition coils? ive checked both coils and they are both good.

 

SA's have both ignitors and igntion coils. The ignitors on an SA are on the back of the control box you see just aft of the coils, there on the fender.

FB's have both, too, but they moved the ignitors on to the actual distributor on the FB's. Coils stayed in the same place on all first gens.

 

Welcome aboard. I see you are a fellow Michigander, so I wanted to tell you that there will be several of us in Lansing at MSU on August 14th & 15th for an autocross. If you can bring it down then, we'd be happy to look it over for you, give you some pointers, answer your questions, and get you addicted to autocrossing all in the same weekend.

Also, you might want to think about shopping around for a used FB distributer with ignitors. That will get you away from the old points system, which can be a major hassle under the best of circumstances.

Good luck... Oh, and stop by the Midwest section of this forum and say hi to the guys...




.

 

Now im even more confused..... my engine bay looks nothing like that.... i dont have that control box, or that wire for the tach..... and my tach used to work, and i never had that wire.....

 

If I can read this correctly, the Yellow wire with green stripe should be the pickup for the tach.
Move that to the negative terminal of the trailing coil and see if you get tach.

 

79 model has the white relay box in DrivingDriver's pic. 80 model has J105 ignitors mounted to the body. Connect the tach wire to the leading on a 79, trailing for 80 on.

 

any idea why my SA doesnt have that box, or the tach wire there. my tach used to work and there never was a wire attached there.

 

First, what year is your SA? Second, the wire colors may vary from year to year, I haven't checked. You can DL the wiring manual for your year from the following link.

http://foxed.ca/foxed/index.php?page=rx7manual

If you don't have the relay box, then you have ignitors. And the box should be silver.

 

its a 79. ive downloaded that but it doesnt seam to be much help... where that silver box is i have these white resistors (i think thats what they are). would the box be somewhere else?

 

Nope, that's it. Looks like you don't have a cover. Tach wire comes off the leading coil for the 79. I should make a correction. It's a resistor box, not a relay box. The coiled wires in the ceramic holders help the charge build up in the coil before it fires.

 

oh ok... so i just gotta find out where the tach wire is. thanks

 

Y/G wire on the - side of the leading tach

 

I'm sure you meant to type coil instead of tach.

 

ok so my tach does work.... kinda..... but it reads idle (750 rpm) at around 4-5 thousand rpm. it seams that its dropping down where its supposed to be... anyone know what would cause this?

 

when was the last time the points were adjusted/changed?

 

the points were changed and adjusted very recently. the car really hasnt been drivin as im doing some body work on it

 

On the SAs, the switchover from voltmeter to tach is controlled by the alternator/voltage regulator and the choke&check relay. The '79s had an external voltage regulator for the alternator. They switched to an internal regulator in '80.

If the tach was not working at all (stuck on volts), I would look at the following:

- alternator (belt not broken, plug connected, etc.)
- check voltage regulator
- check the choke&check relay

If it was any of these, the warning lights would remain ON after the car was started (do they go out when the car is started?).

If it correctly switches over to tach, but just doesn't read the RPMs correctly, then you may have a poor tach signal or could be a defective tach:

- check tach wire connection, check/adjust points, etc.

Are you seeing any other issues? What's the voltage when you go to start the car? When it was stuck in voltmeter mode, what voltage did it read? Any lights dimming, slow cranking, etc?

If you have a voltmeter laying around, hook it up to the battery and start the car and see what voltage you get. You may have a bad alternator or voltage regulator.

Summary: Alt needs to be charging for the meter to switch to tach mode. If it switches over, but the reading is incorrect, the tach signal is bad or the tach is defective.

 

Yes, I had a tach reading 4-5K at idle once. It was ok after replacing the voltage regulator back on the inner fender next to the clutch master clyinder.

 

I had this same issues on my 79 and solved it when I realized that one of the wires from the driver side of the alternator had intermittent connectivity.
In this picture, it was the wire on the lower right of the three wires shown. Remade the connection and the problem went away.