FN 882 A9S what does it really do?

[TT331FB]

ICS dashpot prepostion. X is desired RPM, Y is airflow or is it?

This function doesn't make sense to me.

Anyone care to enlighten me?

[86GT]

It is basically the amount of air at a particular idle point you want the ISC. I believe it is an adder to the desired ISC at an idle. This will hold the RPM at (ISC at idle + FN882) until the VSS reads below 6mph. It will then drop the rest of the way down to normal idle.

The GUFB book states that it is lbs/min.

[TT331FB]

Thanks Clint. Whats missing is what tells the ISC what duty cycle to use at idle. That would make things so much easier. My A9s isn't like the A9L in this respect.

[86GT]

It is there it is FN875N. This function takes the idle, say 672, which has a value of .75 and then subtracts the TB air flow say .55 to get a calculated air of .2. This then can be looked up in FN800 to get the ISC duty cycle.

This .2 air is equal to about 34% DC.

[TT331FB]

OK, This is helping. My TB airflow is almost the same as the air flow at the desired idle speed. This would give a calculated required air of near zero.

But, I have no FN800. Sorry my questions seem to go in circles. I use just the Tweecer only. Perhaps FN800 is only accessable by the EEC editor?

[86GT]

I sure hope that you pull more air than what is in the TB air flow at an idle. the .55 is in lb/min not kg/hr.

Take the idle kg/hr MAF flow and multiply it by 2.2 and then divide by 60. What are you idling at?

Sorry I looked at the A9M for the FN800 not A9S. I'm sure it will be the same as the A9L and A9M. I would not worry about that function anyway. it is the ISC netural function FN875N that you need.

[TT331FB]

I sure hope that you pull more air than what is in the TB air flow at an idle. the .55 is in lb/min not kg/hr.

Take the idle kg/hr MAF flow and multiply it by 2.2 and then divide by 60. What are you idling at?

Sorry I looked at the A9M for the FN800 not A9S. I'm sure it will be the same as the A9L and A9M. I would not worry about that function anyway. it is the ISC netural function FN875N that you need.

Remember that post I made about idle MAFV values equal for both TB and normal idle? Next time, I'm logging both with the spout out, to see what happens, at normal idle. My log did show a ISC duty cycle of 30% but the spark was all over the place.

[86GT]

The spark is supposed to be a secondary idle control. The ISC is supposed to be the primary. At an idle my spark will vary from 18-21.

I almost want to believe the spark is a course adjustment and the ISC is a fine tune adjustment. Idle spark is as follows:

during dashpot
Strategy_______FN839___ * ____FN111
X3Z___________.648_____ * _____30___= 19.44
A9L___________.648_____ * _____31___= 20.08
A9P___________.992_____ * _____30___= 29.76

during netural Idle control
Strategy__________FN841N________ * ____FN111
X3Z___________.602 thru .898_____ * _____30___= 18.06 thru 26.94 No RPM error = 19.56 degrees
A9L___________.484 thru .969_____ * _____31___= 15.00 thru 30.03 No RPM error = 20.00 degrees
A9P___________.453 thru .992_____ * _____30___= 13.59 thru 29.76 No RPM error = 18.06 degrees

This means that the X3Z has the least amount availiable correction whereas the A9P has the greatest. The way the X3Z compensates for this in my opinion is the ISC correction rate(gain). I believe X3Z has a slower correction (Porportion in a typical PID loop) that allows for less overshoot. It also has a steeper gain multiplier FN824 which is more intergral in a PID loop.

In short, the X3Z has a faster reacting ISC and therefore needs less spark control. This is if I am reading all of the numbers right. Man my head hurts after that one.