So on my 1990 IROC I have done a swap of my engine management system to a FAST XFI. I have the E6 ignition box and the dual sync distributor all wired up. The engine (383 sbc build) starts and runs fine. But I have no tach signal. I have wired the 12v square wave signal wire from the ignition control module to the tach signal wire on the c100 plug at my firewall. The tach is dead. The tach worked flawlessly and read correctly before I did the ECM swap. Does anyone have any ideas? I thought the 1990 IROC tachs worked off of a 12v square wave signal. Maybe i'm mistaken. The FAST software program is reading the RPMs accurately off of the signals from the dual sync distributor.



Greg F