The last week or two, I've been fretting a bit about injector open time. I left it at the default of 1.0ms since the beginning, which is said to be "close enough" for most injectors. But with a pulse width of only 1.5ms or so at idle, being a few % out on the dead time can make a difference.
I asked Bosch on twitter, who helpfully said that it was proprietary information so they couldn't possibly tell me.
So yesterday I had a go at calculating it myself.
In tuner studio, there's an engine settings page where you tell it about your engine and injector size, and how many times to squirt per cycle.
You can also see when the engine is running a value called "pulse width", which is how long (in ms) current is applied to the injector each squirt. Pulse width minus open time is actually how long fuel is squirted for.
So, the theory is then that if you hold the engine at a set rpm with a set AFR (say 3000 and 14.0) then the actual fuel delivered per cycle will be the same whatever squirts per cycle is, and you can calculate your injector open time from the differences in the pulse width.
I tried this with 2 and 3 squirts with 1.0ms set.
With 2 squirts, my pulse width is 1.65ms. Take away the 1.0ms for open time, then I've got 2x 0.65ms squirts per cycle = 1.3ms of fuel.
With 3 squirts, my pulse width is 1.425ms.
Take away the 1.0 again and that's 3x 0.425 = 1.275ms of fuel.
Close but not the same.
You can then do the calculation:
openTime = [NumOfSquirt(a)*PulseWidth(a) - NumOfSquirt(b)*PulseWidth (b)]/ [NumOfSquirt(a) - NumOfSquirt(b)]
and I get the answer 0.975 is my open time. So take that Bosch, I've revealed your secret