View Full Version : Tach pulses per revolution

70 LS1
01-13-2006, 05:27 PM
How many tach pulses come from the PCM per revolution. I think it is 2? Is it a 5V squarewave signal?

01-13-2006, 05:39 PM
Yes, the computer puts out 2 pulses per revolution (4cyl output). I am not sure what style signal it is but you can convert it to 4 PPR (standard 8cyl output) by using EFI live 7 or HP Tuners.

01-14-2006, 09:38 AM
Hey jeff,
I donít know if you remember me consulting you on tach problems on my vette. Any way itís an 81. I rebuilt the tach and hooked it directly to the signal from the PCM It works but I suspect that it off a bit. Iím very happy that the tachometer moves again. I just need to get my hands on a programmer and check if the PCM is set on 4 or 8 cyl and play with it.