installed a chevy V8, HEI ignition in a 90 Jeep wrangler that originally had a 4 banger.
I hooked up the tack and it works - but it reads twice teh real RPM (seeing 8 coil pulses when it expects 4 per tach revolution).

Anyone know of a cheap fix for this? I found a website selling a black box that allows you to hook any engine to any tach for $80. I was hoping for a backyard fix...

Any ideas?