Maybe some of you can help me out here. I am wondering what point the megasquirt uses to fire the injectors. Does it start the injector opening when it fires the spark plug?, or does it start the injector opening when a certain tooth passes on the CAS. I am just trying to figure out when my injectors are firing under low load.

The reason I ask is that the injector pulse width is around 4-6ms(low load), and according to what I'm able to calculate the primary intake port is open for about 15ms at 2000rpm(188degrees of primary port opening on a stock S4 NA), and then closed for about the same.

Part of the reason I ask is that I still have some stumble under low load, and am currently running the MS in open-loop. It just doesn't like to run under low load around 14.7:1, yet I used to be able to run 15.5-16:1 like renns was saying in a previous post(with factory ecu and wide band contorller set to run 15.5:1 in closed loop) .

I don't know if this is the best place to ask this, but I just can't seem to find much on the subject.

Thanks, Kris

 

it schedules injection on tach pulses depending on your settings.. so it'll be on the trigger teeth if you're running ignition. How many injections per cycle do you have set up?

Tofuball and I ran as lean as 16:1 on his S5 NA with no stumbling.

 

I have 2 injections per cycle set up right now. I'm also using a stock CAS, I have it set to fire off of teeth 12,2,6,8 In the wheel decoder settings also.

Kris

 

Okay, my head is filled with more questions now haha. Will it trigger the injectors on the 2 tooth wheel or the 24 tooth wheel?

 

it triggers on tooth 12 and 6 for you. On the Ne wheel of course.

You may want to check the ignition timing at the places where you're getting a stumble... try carefully increasing/decreasing the timing and looking at the results. If everything is set up right, you should be able to run pretty lean without stumbling on cruise.

 

Yaaaaaaay, I just replaced my primary injectors with brand new ones, and this completely resolved the stumbling problem. I'm running 14.7:1 afr at the moment with the narrow band O2, and it is as smooth as can be under all load conditions, accell, cruise, light decell etc.

I'm very happy to have resolved the problem, and also very happy that it wasn't my tuning, or the megasquirt causing it

Kris