MSefi.com read only forum (Jan.15,2018)

BBC, dual gm tbi, MSII, V3,code 2.89
I am going on the bases that my injector opening time is 1ms and my total time is 1.35ms at idle. My idle is pretty stable at this setting. I have read that small open times gives idle problems. From practical experience what minimum open time have others dealt with. I have been fooling with variable fuel pressure system to increase my idle open time but it is a lot of interpolation and trial and error work and would not rather do it if it doesn't appear I will gain from it. With the variable pressure I can get my total open times to 1.67ms. I am presently using 2 squirts sim and tried alternating but the motor didn't like it.
thanks

355vette,

Don't confuse opening time with pulse width. These are two different, but related things.

The opening time is meant to represent the time it takes to open the injector (i.e. the time between when the injector signal starts and it actually starts squirting fuel). This is typically 1.0 for a high-impedance injector, and around 0.7 to 0.9 for a low-impedance injector (including most TBI set-ups).

The idle pulse width is much more important with MS-I because it only has 0.1 millisecond injector pulse width resolution. Pulse widths under about 1.7 mean that the tuning occurs in large steps that may make it impossible to get just the right amount of fuel. See: http://www.megamanual.com/v22manual/mtune.htm#idlepw

MS-II has 100x better pulse width resolution, so the issue with idle pulse width has only to do with how accurate the injector open time is. That doesn't even matter, as long as you don't change the req_fuel, number of squirts, or anything like that.

So if you can tune the idle and cruise to work as you prefer, then don't worry about the low pulse width.

Lance.