Is the tach signal coming from the trailing coil positive voltage or ground signal, anyone know? I looked in the FSM and it doesnt show voltage or ohms like the other gauges.

TIA.

 

you need an oscilloscope to read it. there are two signals, G (from the big 2 teeth in the CAS) and Ne (from the small teeth in the CAS).

 

To see if the tach signal from the Trail coils is any good, you need a meter with HZ or Freq feature, if you will.

DC plus.

 

article on the ignition signals: http://www.teamfc3s.org/info/articles/demystifying.html . I would disregard the bottom section about finding TDC.

 

interesting...

 

Ive seen people run an aftermarket tach off the check connector right there (Y/L), so I take it its a standard signal used for RPM and not something RX7 specific? Pardon my ignorance please

 

WOW, good read, thanks a ton for the link.

Now I know a few things:

- The RX7 tach reads similar to a 4 cylinder tach due to an ignition event occurring every 180* of the eccentric shaft.

- The Select signal is a 0-5v signal coming from the ECU that triggers the trailing plugs based on 0 and 5 volts.


So, two questions:

1) Does the tach signal itself vary between 0-5v or 0-12v?

2) Is the tach signal switched on negative or positive voltage?



If anyone can answer these I would be eternally grateful...

 

Buy a Fluke 88. Put it on dc volts. Idle the engine. Put the neg lead on a known gnd. Put the positive lead on the yellow/blue wire at the trail assy. Press the HZ (Freq) button on the meter. You now see the rpm diplayed.

 

Im really not worried about displaying RPM on a multimeter, Im trying to run a non-standard tach signal through the OEM tach and the signals are not compatible. I figured the first step would be to figure out the OEM signal, then match it with a MSD DIS adapter or something.