Just a thought on IAC throttle follower code for TBI
10-24-2003, 10:45 PM
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Car: 91 Red Sled
Axle/Gears: 10bolt Richmond 3.73 Torsen
Just a thought on IAC throttle follower code for TBI
As the topic describes, this is just a thought. Maybe some of the reasons why I hate the stock TBI throttle follower code is because of emissions. It seems to be worse than TPI and all other port injection, might have to do with the transit time from when fuel is introduced to when it is used? I just really can't stant the stock code and I know it isn't the holley IAC. It's apparent in stock form, you rev, it takes TOO LONG for it to rev down.
I can't wait to source code this ecm with romless. I'm going to remove all of the code that is there for emissions only (EGR, AIR, TF, etc.). It's going to be pure EFI, performance with caddy street manners. First things first, progressive throttle linkage cam. The stock straight wire gives me no feel at part to mid throttle. That's gotta change.
Anyways, anybody with a relatively hot motor, keep the throttle follower steps with a stick tranny, else ditch it and limit those counts!
I can't wait to source code this ecm with romless. I'm going to remove all of the code that is there for emissions only (EGR, AIR, TF, etc.). It's going to be pure EFI, performance with caddy street manners. First things first, progressive throttle linkage cam. The stock straight wire gives me no feel at part to mid throttle. That's gotta change.
Anyways, anybody with a relatively hot motor, keep the throttle follower steps with a stick tranny, else ditch it and limit those counts!
10-25-2003, 12:32 AM
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Car: An Ol Buick
Engine: Vsick
Transmission: Janis Tranny Yank Converter
RBob's IAC article goes along way to explaining how to edit it.
It takes alot of dithering to get it right thou.
The T/F and AE run hand in hand as the throttle opens.
I think following the lead of the later aftermarkets in this one area, is an idea worth following.
Basically just tracks the throttle opening, and then a tuneable delay for closing TPS.
Too fast of closing throttle follower can make for stalls in the bleach box.
TBI is somewhat worse since your dealing with a wet manifold and at sudden closure the wet walls instantly evaporate, and leaves it rich, for an instant or longer.
It takes alot of dithering to get it right thou.
The T/F and AE run hand in hand as the throttle opens.
I think following the lead of the later aftermarkets in this one area, is an idea worth following.
Basically just tracks the throttle opening, and then a tuneable delay for closing TPS.
Too fast of closing throttle follower can make for stalls in the bleach box.
TBI is somewhat worse since your dealing with a wet manifold and at sudden closure the wet walls instantly evaporate, and leaves it rich, for an instant or longer.
10-25-2003, 09:55 AM
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Car: check
Engine: check
Transmission: check
The IAC, friend or foe? Can it be tamed? Only the Shadow knows. . .
Yes, part of the IAC function is for emissions. On a throttle lift it helps prevent a slug of rich fuel making its way out the tail pipe. The IAC does this by staying open and slowly decaying back to normal.
In stock form the throttle follower action is too much. I like to set it so it reaches max IAC with 100% TPS. Then I also get rid of the closing delays and increase the closing rate.
On the '8746 the IAC also gets a kick when the P/S switch is active.
Here are the throttle follower terms:
I haven't seen a delay term for when the throttle is lifted, befor ehte IAC starts to close. It may be there, don't know.
The last two (LD542 & LD543) control how much the IAC moves relative to the TPS. Smaller number makes it move less.
The three filter coef terms (LD539. . .) control how quickly the throttle follower (TF) steps decay out on a throttle lift. A larger number will cause the TF steps to decay faster.
The two MPH terms (LD53E . . .) define which of the three filter coeficients are used. Plus the low MPH term is used for the min TF steps at LD540. the minimum steps are always applied until the MPH is less then the lowest MPH threshold.
The bias term (LD541) is the TPS threshold that the TPS must be greater then to get TF action.
I like to set the max TF steps (LD538) to a high value as to get as much airflow as possible.
Can check the data logs comparing the IAC steps to TPS% for an idea of how the TF steps operate. Also check when DFCO becomes active as this will add IAC steps.
RBob.
Yes, part of the IAC function is for emissions. On a throttle lift it helps prevent a slug of rich fuel making its way out the tail pipe. The IAC does this by staying open and slowly decaying back to normal.
In stock form the throttle follower action is too much. I like to set it so it reaches max IAC with 100% TPS. Then I also get rid of the closing delays and increase the closing rate.
On the '8746 the IAC also gets a kick when the P/S switch is active.
Here are the throttle follower terms:
Code:
LD538: FCB 96 ; max TF steps LD539: FCB 32 ; TF decay filt coef, < low mph LD53A: FCB 16 ; TF decay filt coef, > low mph & < high mph LD53B: FCB 25 ; TF decay filt coef, > high mph LD53C: FCB 64 ; filt coef (L00BF, for DFCO & kickdown steps) LD53D: FCB 15 ; filt coef (L00C1, for P/S Sw, Baro) LD53E: FCB 5 ; TF decay low mph thres, between filt coef @ D539 & D53 LD53F: FCB 20 ; TF decay high mph thres, between filt coef @ D53A & D5 LD540: FCB 10 ; min TF steps if mph > low mph (LD53E) LD541: FCB 6 ; 2.3%, TF tps% bias LD542: FCB 32 ; TF factor in prk/neut LD543: FCB 64 ; TF factor not in prk/neut
The last two (LD542 & LD543) control how much the IAC moves relative to the TPS. Smaller number makes it move less.
The three filter coef terms (LD539. . .) control how quickly the throttle follower (TF) steps decay out on a throttle lift. A larger number will cause the TF steps to decay faster.
The two MPH terms (LD53E . . .) define which of the three filter coeficients are used. Plus the low MPH term is used for the min TF steps at LD540. the minimum steps are always applied until the MPH is less then the lowest MPH threshold.
The bias term (LD541) is the TPS threshold that the TPS must be greater then to get TF action.
I like to set the max TF steps (LD538) to a high value as to get as much airflow as possible.
Can check the data logs comparing the IAC steps to TPS% for an idea of how the TF steps operate. Also check when DFCO becomes active as this will add IAC steps.
RBob.
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