A possible issue depending on your EFI fuel system PSI and car: A good fuel pump. The fuel system has been the biggest pain on mine. The EFI system itself isn't any trouble at all. I'm running a Mass-flo EFI system and have an Anderson Ford Motorsport computer to put on when I put it all back together because I hate that the Mass-flo system gives you zero feedback. The fuel system I've ended up with as an Aeromotive a1000 stealth sump built into a stock tank.