TB AIR Clarification

Vehicle specific forum for tuning the Foxbody Chassis Mustangs utilizing the LUX0, GUFA, GUFB, and GUF1 Strategy

TB AIR Clarification

Unread postby 89FiveOh » Wed Feb 28, 2018 10:23 am

Hello,
When dialing in idle air, I adjust the TB screw to achieve the lowest possible idle and log the airflow without IAC help and input that into my ISC Idle Neutral Air table. I enter that airmass into my TB air scalar since all the air entering the engine was without IAC contribution. I should never have to adjust the TB screw again? Also, I should not have to change the TB airflow SCALAR again?

Now when I enter a NUBASE, the only scalar changes will be the logged IAC duty cycle air contribution to the new NUBASE? If the NUBASE entered will exceed a duty cycle of ~35%, then it might be appropriate to increase the TB set screw to allow the duty cycle to be within range of my 35% target? If a change to the setscrew is required, I would have to calculate the new TB airflow again without any IAC help and change the above mentioned SCALARS to represent the new airflow? The TB airflow scalar should ALWAYS be the airflow without IAC help and it should NEVER change unless the screw has been adjusted again?

Also, how to combat an RPM higher than the DSRDRPM? For example, my NUBASE is 800, my DSRDRPM is 800, but my actual dashboard RPM is 890-900 range?

Thanks for the insight
89FiveOh
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Re: TB AIR Clarification

Unread postby decipha » Wed Feb 28, 2018 12:22 pm

the idle air write up on the homepage has all the info

the t/b airflow scalar is the amount of air through the throttle body correct, fn875 is the airmass for a given rpm correct

anytime you change the maf transfer you change that calculated airmass and will need to adjust both of those parameters to keep it accurate

if the engine idles with the iac unplugged theres no reason to raise the idle so much that the iscdc needs to exceed 35%, in any case, anytime you adjust the set screw you have to recalc the t/b airmass and update fn875 the idle airmass function for the new airmass

correct, the t/b airmass scalar is the airmass through the throttle body

if the idle rpm is higher than dsdrpm then that means you've screwed up the airmass calculation somewhere and the ecu can't reach the target DSDRPM or its not setting the idle flag, when actually dialing in the idle airmass the engine has to be warm and stable and fn1862 the isc multiplier table has to return a multiplier of 1 for that cell your in

its a lot of work to actually dial in idle airmass the way ford intended, much easier to just throw in the a9l2 and adjust the throttle stop until ipsibr is near 0 - done and isn't affected by the maf transfer
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Re: TB AIR Clarification

Unread postby 89FiveOh » Wed Feb 28, 2018 1:02 pm

Sooooooo, If my engine idles at lets say 750, without IAC help, I should just enter that as my NUBASE and go with it?

Any RPM adder requirements in play, the IAC will handle?
If my NUBASE is in fact the lowest possible idle without IAC help, what should my MIN ISC Airmass Scalar be, 0.00 lbs/hr?

Also, after achieveing the lowest possible idle, lets say 750, and for whatever reason, I want my NUBASE to be 800 for example, the only thing I have to do is enter my new NUBASE and thats it? No need to worry if my new RPM I want shoots my DC up to lets say 50%?

I like the mechanical idle you mentioned, but as a challenge, Im trying to stick to Mr Ford’s way for now as a way to learn.

thanks
This site is the best as well as your writeups. However, myself, I find that the writeups you provide, would suit me better with an orientation class first. LOL.

I ask these questions, but not before reading your writeups first, and many many times...
89FiveOh
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Posts: 40
Joined: Thu Jan 11, 2018 5:13 pm
Name: Andy Borden
Vehicle Information: 1989 Mustang GT
GUFB A9L
Binary Editor/EEC Anaylyzer
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MOATES QuarterHorse
308
Custom Cam (HR)
AFR 165, 58cc
BBK 75mm (24lb/hr calibration) MAF
5 speed
3.73 gears
NA
Full length BBK headers with H-pipe thru Flowmaster mufflers

Re: TB AIR Clarification

Unread postby 89FiveOh » Wed Feb 28, 2018 2:59 pm

The only thing thats got me confused now is:

The scenerio that NUBASE is maintained without IAC help, whats the value to enter for DEBYCP? 0.00?

If I enter 0 for DEBYCP, and the EEC calls for 50% DC, will the IAC just be giving it 50% more 0? Or is the amount of air always rely on the ISC xfer function and not the value I enter for DEBYCP?

Thanks
89FiveOh
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Posts: 40
Joined: Thu Jan 11, 2018 5:13 pm
Name: Andy Borden
Vehicle Information: 1989 Mustang GT
GUFB A9L
Binary Editor/EEC Anaylyzer
Innovate MTX-L PLUS
MOATES QuarterHorse
308
Custom Cam (HR)
AFR 165, 58cc
BBK 75mm (24lb/hr calibration) MAF
5 speed
3.73 gears
NA
Full length BBK headers with H-pipe thru Flowmaster mufflers

Re: TB AIR Clarification

Unread postby decipha » Wed Feb 28, 2018 6:06 pm

debycp is a development scalar to min clip the iscdc, you can set it to 0 i always do, its completely unrelated to dialing in idle air

if u set nubase to the minimum idle rpm with the iac unplugged when u do plug the iac in the idle will raise a touch and nevrr maintain idle correctly, in a perfect world the iscdc should be 15% at a warm stable idle, basically the iac is off

anytime u raise the idle rpm scalar nubase u shouldny have to make any adjustments so long that you have to fn875 the idle airmass function dialed in for the rpm you want
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91 4r70w - Skarlett
92 (2x) 5spd & auto - Bianqa, Andrea
93 auto - Danika
94 5spd Rionda
95 auto Aisha
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