I just put new coils in (Accel 8140 Super Stock) my REX. They definately helped my cold start idle. Now, my tach is jumping after it warms up.

Could this be due to a bad ignitor?

 

Yes, it could. Try swapping the tach send wire to the other coil and see if it changes (bad ignitor) or not (something else).

 

check and make sure the wiring is tight and has a clean connection on the trailing coil. is the engine surging too, or just the tach jumping. the easiest way to check the igniter is to exchange the two and see if it still does it.

 

The engine is running very smooth. Still no power at high rpm though (different thread).

Tach send wire? the only connections I made were the ground and the dist.

The ground was a clip so I don't know if any other wires were attached. I have a factory service manual and it made no mention of a tach send wire.

 

the negative wire on the trailing splits and one goes to the tack. i was thinking this connection could be loose. i'd check your igniters. mine did this kind of thing, but it was welds falling of into the alternator shorting it out.

 

OK, it just got stranger (more strange?). The tach only jumps when idling AND the lights are on. As soon as I turn of the headlights, no more jump.

 

i'd say alternator just because that what caused mine. turning on the headlights is causing an electrical drain. i'd take it to advance or autozone and have them test the alt.

 

The battery/electrical guage shows 13-14V when running with or without lights. Also, I think the alternator is only about 10K mi. and is a Mazda part.

 

I have the same problem and I just replace the alternator with a 70amp, not the usual 60amp.

The tach light seems dull when it starts jumping, which is very noticeable since I have an Autometer monster tach.

I have already switched the coils and still the same result, so I imagine that the tach isn't powered or grounded properly.

 

your tach is either getting a voltage spike or is losing the signal. the only thing i can say is go through the wiring from the coil back. time to get the haynes out and get dirty. find all important points and then f with them while someone watches the guage. sorry guys that all i have. a bad connection somewhere.

on mine, as the alt would short and throw the switches in my external regulator, the tach would go between reading volts and converting to rpms. not sure where that electrical conversion is but could be a problem point too.

 

I figured I had a bad connection somewhere, but my turbo timer shows a pretty steady voltage.

One day when I am bored I will dig up the wires and see what these yo-yo's did to my car.

 

could be bad plug wires , if it didnt have the problem before you upgraded the coils... wires cant hold the x-tra juice.... bad igniter???? dosnt seem possible, usally when they go bad they dont work!

 

I replaced the wires, coils, plugs, alternator, distributor cap/rotor and both ignitors.

I will look for the power source of the tach tomorrow.