Author Topic: Injector Duty Cycle & AFM questions (Read 7301 times)

bearsbmw · « **on:** November 24, 2008, 12:43:42 AM »

Im sure AFM Controls Injector duty cycles so then a fully open AFM door flap would be 100% duty cycle ?

Does the O2 sensor signal also have influence over duty cycle when in WOT

The reason I ask is I have a very intresting idea im going to try with a 02 simulator, bigger injectors, and some afm door figeting and my 12psi of boost and my crude tune

roundel318 · « **Reply #1 on:** November 25, 2008, 02:08:43 PM »

I believe O2 readings are tossed at WOT.

bearsbmw · « **Reply #2 on:** November 25, 2008, 07:18:03 PM »

Quote from: roundel318;61674

I believe O2 readings are tossed at WOT.

Ahhh yes stupid me ... back to the drawing boards

Cristian G in Oz · « **Reply #3 on:** November 25, 2008, 07:21:07 PM »

Also injector duty cycles are usually indexed with TPS and engine speed as well.

bearsbmw · « **Reply #4 on:** November 25, 2008, 07:25:36 PM »

so I would need to find a stock fuel map to actulay know 100% correct?

bearsbmw · « **Reply #5 on:** November 25, 2008, 07:29:28 PM »

anybody know where I could find a map?

roundel318 · « **Reply #6 on:** November 25, 2008, 09:41:39 PM »

I remember reading somewhere that WOT was like 105 or 110%?

bearsbmw · « **Reply #7 on:** November 25, 2008, 10:02:15 PM »

Quote from: roundel318;61698

I remember reading somewhere that WOT was like 105 or 110%?

Sweet! some insurance would be nice and it would realy help with my injector selection

Cristian G in Oz · « **Reply #8 on:** November 26, 2008, 05:59:03 AM »

Quote from: roundel318;61698

I remember reading somewhere that WOT was like 105 or 110%?

I'm not so sure about this. If your talking about duration of opening it is impossible to have more than 100%:confused:. Even 100% open is very bad as your injector never closes:(.

I know for MoTec they recommend no more than 80% IJPU. Over that the injector gets inefficient and can cause more problems than it's worth.
I know when we had IJPU on the E30 M3 that was at 82%-83% across 4 cyl's we got some weird readings from the ECU.
When we changed to bigger injectors problems went away.

tjts1 · « **Reply #9 on:** November 26, 2008, 08:55:25 AM »

Over about 80% duty cycle, injectors start to lose accuracy. At 100% the injector essentially stays open continuously and can be damaged.

roundel318 · « **Reply #10 on:** November 26, 2008, 01:17:03 PM »

Perhaps I am confusing this figure for something else, I anticipate the actual figure

bearsbmw · « **Reply #11 on:** November 26, 2008, 07:36:00 PM »

Quote from: roundel318;61744

Perhaps I am confusing this figure for something else, I anticipate the actual figure

it's killing me haha

roundel318 · « **Reply #12 on:** November 27, 2008, 02:36:40 PM »

I think I was confusing the 105/110% number for the TPS figure at WOT, not injector duty cycle, now that I think about it

bearsbmw · « **Reply #13 on:** November 27, 2008, 03:03:27 PM »

I might be on to something so fantastic and cheap you will all be looking for a AFM driven car forever

will keep updating

bmwman91 · « **Reply #14 on:** November 28, 2008, 11:49:59 PM »

The injector duty cycles are controlled by (in no particular order):
AFM (primarily)
Intake Air Temp.
Coolant Temperature (warm-up enrichments)
Throttle Position
Exhaust Gas Oxygen Content*

*The O2 sensor's input is only used below 85% throttle & 4000RPM, if I recall correctly.

Keep in mind that the AFM's signal is the load-variable's primary input, and that ignition timing is directly affected by the ECU's computed load value at a given instant. Tweaking it might cost you some performance due to incorrect ignition timing, or a whole motor.

What exactly are you working on here? I saw evidence of boost......