a4sfed928

Has anyone captured the tachometer signal for the early CIS cars? I am trying to understand the fuel pump cutoff circuit inside the fuel pump relay but I can't make sense of it based on a 0 to 12v square wave.
Any help would be appreciated.

Brian.

a4sfed928

After studying the fuel pump relay pcb I think the ignition module must stop sending pulses to the fuel pump relay above 6300 rpm.

GlenL

Considering the distributor is producing RPM x 4 pulses I'd be surprised if the box was multiplying it that high. Or multiplying it at all.

a4sfed928

I was referring to the engine rpm at 6300 rpm. I seem to remember someone saying the tachometer signal is actually 206 Hz at 6300 rpm

GlenL

Sensible. That's about RPM/60 * 2 = 210. Or a half of a wave per spark ignition.

Lizard928

It is a square wave signal.

The distributor is rotated at 1/2 engine speed.
Count the contacts in the distributor to determine how many pulses per revolution then *desired rpm.