Tach died some time ago for no apparent reason. Digging thru the archives I see a lot of discussion that centers around the "TD signal". I see that as another term for "engine speed sensor". Correct me if I'm wrong.

New Deka Gold battery. Car fires right up. Idles smooth and accelerates the same. Car runs great. No tach at idle or any speed. Stays at zero at all times.

It would seem if I had no TD signal, the car might not run long after starting, if it were to start at all.

This vehicle has a MAS with a tach port. I suppose that could be defective.

Is my thinking about the TD signal correct?

Thanks.

The "engine speed sensor" is a magnetic pickup that is triggered by segments on the flywheel. It is an input device to the MAS. The TD signal is an output signal from the MAS. The TD signal can be checked at the port/terminal with a voltmeter. If the voltmeter incorporates a tach setting, so much the better; in any case just about any voltage of about +3 or more will be sufficient to drive the in car tach.

Frank:

Thanks for the post. That clears up some things.

TD signal * OUTPUT * drives tach

I'll pull the MAS and jumper pins 1 & 2 to run fuel pump relay so car will start; then check the tach port.

I should clarify just a bit I think; the trigger signal from the speed sensor goes first to the ignition control unit (EZL), and from the EZL the TD pulse is sent to the MAS and the in-car tach.