FAST 90/90, IAC steps vs area?
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Joined: Mar 2002
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From: East Central Florida
FAST 90/90, IAC steps vs area? Working with a car that has a new intake, the idle is
hanging when rolling. Main recent changes are big cam
and the intake / TB. Might be a vacuum leak somewhere
but it's been looked for already. The cracker table (it's
a '00) looks pretty sane, not ugly like mine ('02) stock.
I think it's just getting a lot more air than it's calculating.
I'm suspecting maybe the 90mm TB just has a different
true area, maybe area vs steps too. I've seen people talk
about shifting the table left or right. If anyone has made
a table that works well, I'd appreciate a link or a snippet.
hanging when rolling. Main recent changes are big cam
and the intake / TB. Might be a vacuum leak somewhere
but it's been looked for already. The cracker table (it's
a '00) looks pretty sane, not ugly like mine ('02) stock.
I think it's just getting a lot more air than it's calculating.
I'm suspecting maybe the 90mm TB just has a different
true area, maybe area vs steps too. I've seen people talk
about shifting the table left or right. If anyone has made
a table that works well, I'd appreciate a link or a snippet.
TECH Apprentice
Joined: Oct 2004
Posts: 360
Likes: 0
From: Katy, TX
I shifted mine down (EFI Live) and zeroed out the values before. I ended up having to move mine down 12 places because I have 26 in. of vacuum at idle and it still wanted to stay up in the RPM's. There's really no need to manipulate the values once you find the sweetspot of where to shift it. You'd be surprised how much cracker you can take out, even on a big cam car with the 90/90. Also, it might make your life easier to bump up the idle speed overflare spark reduction.
Originally Posted by J-Rod
Good threads here... Most of this is realted to idle. Also, the stock TB can get a bit better with some porting. I've also noticed when you dial the tables especially throttel cracker, the thing sometimes gets "sloppy" and you have to give it more throttle.
Just keep in mind a lot of values are going to increase or decrease about 48% based on the new Tb's effective area. But, if its based on airflow, then what you will need to do is log desired air, etc... to make sure things like desired air matches.
Also, you need to look at Idle airflow vs ect
log airflow data vs coolant temp and re-do that table.
Also, you may need to look at things like:
Throttle Cracker Airflow
Throttle Follower Airflow
Throttle Follower Airflow vs TPS
Throttle Follower Decay Gear vs Speed
C5 - ETC Scaler on 90mm TB, question
https://ls1tech.com/forums/pcm-diagnostics-tuning/434267-c5-etc-scaler-90mm-tb-question.html
Update 90mm TB + 48% Effective table
https://ls1tech.com/forums/pcm-diagnostics-tuning/335186-update-90mm-tb-48-effective-table.html
Is there anyone who has a big cam with no surging?
https://ls1tech.com/forums/pcm-diagnostics-tuning/404894-there-anyone-big-cam-who-doesn-t-have-low-rpm-surging.html
Throttle follower, throttle cracker, running airflow. (see the tables that were posted, and look at them)
https://ls1tech.com/forums/pcm-diagnostics-tuning/400278-issue-raf-table-stit-ltit.html
Simple facts are:
75mm Throttle Body and 90 Throttle Body. 48% is not related to airflow, it is the percentage of step that the 90mm uses to mimic the 75mm Area. So.....
Hypothetically
IF a 75mm TB @ 40 steps has 1 cu/inch of area
Than
a 90mm TB would need 19.2 steps to have the same 1 cubic inch of area
So you need to....
Multiply the 40 steps by .48 to get 19.2
40 x .48 = 19.2
There is alot more to the calculation but this is the jist. Rather than using steps since the step is going to be linear and equally sized, I used 0 to 90degrees and calculated area based on .25 degree. Calculated area when open - area closed to find total area gained, divided that by my 360 steps(360 - 1/4 or .25 degree increments) to find total area for each 1/4 degree of throttle movement. I used that to make a chart to map area of the 75mm TB as the butterfly opens from 0 to 90 degrees or WOT. I made another chart based on the area as it gained and reversed solved the 90mm TB to find the required step to mimic the exact area that the 75 shows. The steps were 48% less in each calculation. So reguardless of what unit that the ECU uses this calculates the same thing.
Just keep in mind a lot of values are going to increase or decrease about 48% based on the new Tb's effective area. But, if its based on airflow, then what you will need to do is log desired air, etc... to make sure things like desired air matches.
Also, you need to look at Idle airflow vs ect
log airflow data vs coolant temp and re-do that table.
Also, you may need to look at things like:
Throttle Cracker Airflow
Throttle Follower Airflow
Throttle Follower Airflow vs TPS
Throttle Follower Decay Gear vs Speed
C5 - ETC Scaler on 90mm TB, question
https://ls1tech.com/forums/pcm-diagnostics-tuning/434267-c5-etc-scaler-90mm-tb-question.html
Update 90mm TB + 48% Effective table
https://ls1tech.com/forums/pcm-diagnostics-tuning/335186-update-90mm-tb-48-effective-table.html
Is there anyone who has a big cam with no surging?
https://ls1tech.com/forums/pcm-diagnostics-tuning/404894-there-anyone-big-cam-who-doesn-t-have-low-rpm-surging.html
Throttle follower, throttle cracker, running airflow. (see the tables that were posted, and look at them)
https://ls1tech.com/forums/pcm-diagnostics-tuning/400278-issue-raf-table-stit-ltit.html
Simple facts are:
75mm Throttle Body and 90 Throttle Body. 48% is not related to airflow, it is the percentage of step that the 90mm uses to mimic the 75mm Area. So.....
Hypothetically
IF a 75mm TB @ 40 steps has 1 cu/inch of area
Than
a 90mm TB would need 19.2 steps to have the same 1 cubic inch of area
So you need to....
Multiply the 40 steps by .48 to get 19.2
40 x .48 = 19.2
There is alot more to the calculation but this is the jist. Rather than using steps since the step is going to be linear and equally sized, I used 0 to 90degrees and calculated area based on .25 degree. Calculated area when open - area closed to find total area gained, divided that by my 360 steps(360 - 1/4 or .25 degree increments) to find total area for each 1/4 degree of throttle movement. I used that to make a chart to map area of the 75mm TB as the butterfly opens from 0 to 90 degrees or WOT. I made another chart based on the area as it gained and reversed solved the 90mm TB to find the required step to mimic the exact area that the 75 shows. The steps were 48% less in each calculation. So reguardless of what unit that the ECU uses this calculates the same thing.
I used this method. Took about three iterations to get it correct but not only was idle better, but part throttle response was much crisper. The hardest part was getting cold data so that you start high in the IAC counts.
https://ls1tech.com/forums/showpost....6&postcount=30
The problem with just shifting a set amount is that the tables for 1999 and 2002 are different, so if one works, that means the other must be off. Also it will depend upon how much your TB is open.
https://ls1tech.com/forums/showpost....6&postcount=30
The problem with just shifting a set amount is that the tables for 1999 and 2002 are different, so if one works, that means the other must be off. Also it will depend upon how much your TB is open.
