Tach not working under 1.5k

[Pomorza]

Hello guys,

This past weekend, among other things, I replaced my stock 76 distributor and coil with one from an 81 ZX. The Z runs a bit better but the tach refuses to work under 1500 RPM. For what I remember don't I have to add a resistor or something to make the tach work properly?

Thanks greatly

Jan

[Zed Head]

You didn't provide the details or reason for your swap, but I had a problem with my tach after modifying the ignition system and found that an extra condenser/capacitor on the coil negative post fixed the problem. But my tach needle would just bounce and jitter at zero, it's not clear in your case what you mean by "not work". I swapped all of the 76 parts out though, so this might not help your situation.

You do know that the 76 coil is a low current coil and uses a ballast resistor to drop the voltage when running, but the 81 coil has no ballast resistor and uses the full 12 volts and full current. Did you do any other modifications or just swap the coil?

Edit - just saw the part about the 81 ZX distributor. So you're using the E12-80 module? Did you disconnect the 76 ignition module by the fuse box? It's not necessary any more. Maybe it's interfering. You can just disconnect each wire and cover them up to avoid shorts, since some of them are hot when the key is on.

Edited January 11, 2012 by Zed Head

[Pomorza]

Zed Head,

I believe I am indeed using the E12-80 module yes. By not work I mean, until it reaches say 1600 rpm the tach just sits at 0 or as you say bounces. Where is this said ignition module?

[Zed Head]

The black box on the side of the 81 distributor is the new ignition module. Your original ignition module is close to the fuse box in the passenger foot well. If you just stuck the 81 distributor in and connected wires to it, then your old one is still there, but useless. I really don't know if it would affect the tach or not, even though it is still a branch on the blue wire circuit. You can't disconnect the blue wire in the engine bay because it feeds the tach and the ECU.

It wouldn't hurt to crawl up under there and disconnect it to see what happens. If you still have the problem, a small capacitor, like the one off the alternator, is worth a try. It will absorb some electrical noise that the new coil might be producing. Also, you might have disconnected the original one when you made the swap.