tach learning, viper 791xv on 1991 240sx

hey guys. i have a 791xv hooked up on my car, but i can't get it to learn the tach signal. im almost 100% sure i have the right tach wire (it shows 1-6volts ac). I try to get it to learn, but it just won't. i know i have the valet switch on correctly because i can program the alarm's features. i'm pretty sure i have the remote start system hooked up right also. The car will try to remote start (i have a manual tranny so i hold the clutch down) and will start for a split second. The shutdown diagnostic code its giving me is a low or no rpm error. Im guessing this is because it didnt learn the tach, and im sure im doing it right (turning the car on with the key and holding the valet switch). The led never turns solid, and i know i have this hooked up. Please help, i have tried everything.     

Take it out of tach learning  mod and put it in current sensing it should correct the problem.If not put it to fuel injector,wire to get a stronger wire.Jamaica home of the worlds fastest man.