pcmhacking.net

Can someone please advise exaclty what changes from single vs double fire option for injection on 11p systems

All the early EFI systems (VN-VS except ecotec) run in what is known as batch fire operation which means all the injectors fire (inject fuel) at the same time. This happens twice per engine cycle which is where you get the term double fire from. When the system changes to single fire the injectors only fire once per engine cycle. This happens because at idle/low engine speed the injector PW time is to short (less than the minimum PW) for the injector to operate correctly so changing to single fire means the injector PW doubles and allows them to operate correctly. This is also convenient when running large injectors, you can adjust when you transition from single to double fire so you don't over fuel at low engine speeds when you would get an excessive amount of fuel in double fire mode (even at minimum PW) with much larger injectors.

awesome man that makes more sense thank you

Excellent description. But note that you need accurate opening time and voltage vs flow rate data, else you'll get an obvious hiccup when it happens and real world fueling changes. If you get such a hiccup, then look at the opening time versus voltage tables and data. When its right, you shouldn't notice the change from double to single other than you can continue to inject small amounts of fuel with stability where you could not before. Hard to get right, but a nice extension.