FAST 92 startup problem
10-03-2014, 10:47 PM
#1
FAST 92 startup problem Hey guys, I'm having an issue I cant seem to rack down. Basically the car has been tuned professionally then I have been messing with it also down low for idle. The problem is that under normal start conditions with the ac off the car will fire off and idle on its own without issue no matter the temp..
However if I try to start it with the a/c on it will fire initially but then immediately die and I have to open the throttle for a 10 secs. I have tried adding upp to 3 grams extra in the RAF and no change then I added to the start up friction airflow...None of this has helped.
I'm thinking it could be the IAC not giving enough airflow due to the small opening. My IAC counts are usually around 180 at startup. If I cant get it sorted I may just go to an NW 102. Does anyone know why this would happen?
However if I try to start it with the a/c on it will fire initially but then immediately die and I have to open the throttle for a 10 secs. I have tried adding upp to 3 grams extra in the RAF and no change then I added to the start up friction airflow...None of this has helped.
I'm thinking it could be the IAC not giving enough airflow due to the small opening. My IAC counts are usually around 180 at startup. If I cant get it sorted I may just go to an NW 102. Does anyone know why this would happen?
10-04-2014, 01:26 AM
#3
IAC effective area is for tuning the IAC port's dimension from what I understand. The FAST has a small one. As long as you have some steps, it may not help. But you could add 2-3 steps across the board to see what that does.
Can you start it and then turn on A/C? Or does it need to fully warm up before A/C won't bog it down?
Usual questions: add 50 RPM across the board for A/C in Gear and P/N?
-Did you mess with the Adaptive Idle Airflow for the A/C measures? 4.5g and -.050 for max/min and -.050 for the offset?
-Have you logged your STITs with the A/C on to see what it's doing (you must if you know IAC counts). How far off are the STITs?
-Did you run Russ K's cfg file for idle counts with A/C on?
Can you start it and then turn on A/C? Or does it need to fully warm up before A/C won't bog it down?
Usual questions: add 50 RPM across the board for A/C in Gear and P/N?
-Did you mess with the Adaptive Idle Airflow for the A/C measures? 4.5g and -.050 for max/min and -.050 for the offset?
-Have you logged your STITs with the A/C on to see what it's doing (you must if you know IAC counts). How far off are the STITs?
-Did you run Russ K's cfg file for idle counts with A/C on?
10-04-2014, 07:46 AM
#4
I havent logged it with a/c on as I was told thats a no no. It will just not start with the a/c on once it fires it will idle just fine even if I turn ac on. I do know that with it on it generally corrects about 2 g/sec with the a/c on. I have logged my stits but I'm going to run the config again this morning and see what it says.
So does the iac effective area effect startup? I understand what it does and it the pcm "thinks" the air passage is soo small or too big how can it accurately open the iac enough to start it.
So does the iac effective area effect startup? I understand what it does and it the pcm "thinks" the air passage is soo small or too big how can it accurately open the iac enough to start it.
10-04-2014, 08:03 AM
#5
I have seen people say mess with it and others say don't. I am tuning my FAST 102 right now and as long as the VE Tables are right, Spark is good, and the RAC is in-line, I think it IAC works, even with the FAST (though it could be better).
Run the Russ K cfg in idle with A/C on. I had to run it four times: A/C OFF - Gear and P/N; A/C ON - Gear and P/N as the RAF changes for each one of those. But being that you're manual, there is no RAFIN need for you in P/N.
Do it without Adaptive Idle to get the RAC values. And then I'd set it maybe closer to 3 g/sec and -.5 g/sec Max/Min so it can correct. And I'd leave A/C off when you crank. That's a big load on the car. Get the car to fire up then turn A/C on. You can always add 1-2g/sec to the startup airflow if you have any hard cranking issues.
Run the Russ K cfg in idle with A/C on. I had to run it four times: A/C OFF - Gear and P/N; A/C ON - Gear and P/N as the RAF changes for each one of those. But being that you're manual, there is no RAFIN need for you in P/N.
Do it without Adaptive Idle to get the RAC values. And then I'd set it maybe closer to 3 g/sec and -.5 g/sec Max/Min so it can correct. And I'd leave A/C off when you crank. That's a big load on the car. Get the car to fire up then turn A/C on. You can always add 1-2g/sec to the startup airflow if you have any hard cranking issues.
10-04-2014, 11:22 AM
#7
heres another config i ran this morning do these results make sense to anyone? the car is an 02 camaro with 243 heads, 230/232 114 lsa cam bolt ons EWP, and a FAST 102/92. Before the fast with the same mods it was happy with around 9 g/sec at hot idle so how does it make sense that with a bigger intake that would be less?
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10-04-2014, 06:22 PM
#8
Yeah, RAF. I was tired. Running airflow lol.
Anyway, I'd close your TB a little to get your IAC counts up a little. That gives you a little more wiggle room. You'll need to rerun this after you mess with that. Also, try to mark it in case it makes your car angry. Same with the tune - save as a backup. Once you start adjusting the set screw it becomes really hard to get everything to play nice.
The bigger throttle body needs less running airflow as well. I have the 102 on mine and my desired airflow is around .290 lb/min at 196 where you're at .739. The big cam also has a kPa in the mid 70s where you are mid 50s.
But your STITs are like -60. That's because your RAF is off. Input the new values and retest (and do that before you change the set screw). Do one change at a time. See how the IACs look. They might come up a little.
Anyway, I'd close your TB a little to get your IAC counts up a little. That gives you a little more wiggle room. You'll need to rerun this after you mess with that. Also, try to mark it in case it makes your car angry. Same with the tune - save as a backup. Once you start adjusting the set screw it becomes really hard to get everything to play nice.
The bigger throttle body needs less running airflow as well. I have the 102 on mine and my desired airflow is around .290 lb/min at 196 where you're at .739. The big cam also has a kPa in the mid 70s where you are mid 50s.
But your STITs are like -60. That's because your RAF is off. Input the new values and retest (and do that before you change the set screw). Do one change at a time. See how the IACs look. They might come up a little.
10-04-2014, 08:15 PM
#9
what units are you looking at to see it the -60's? I have mine i g/sec and i was seeing around -6 which is still off lol. I reset the iac to see now around 30 counts which I heard is in the range of hat you want for a cammed car. I t was in the 20's with the ls6 setup and worked great.
Btw are you sure you havent tuned before lol I've messed around with this stuff off and one but I know I wasnt that proficient the first week i had it! I uploaded my revised tune on the hpt forum, check it out. I dont quite understand how to properly scale down the ve. My LTFTS were around 3 at idle, i thought that told me if anything the ve was a little lean
Btw are you sure you havent tuned before lol I've messed around with this stuff off and one but I know I wasnt that proficient the first week i had it! I uploaded my revised tune on the hpt forum, check it out. I dont quite understand how to properly scale down the ve. My LTFTS were around 3 at idle, i thought that told me if anything the ve was a little lean
10-04-2014, 10:20 PM
#10
I didn't look closely. You're running a MAF. The VE table doesn't come into play. I am doing SD and it's easier to just scale the VE table down to lean the car out.
What you can do is use the bi-directional controls (after you turn off adaptive spark) in the scanner and lean it out to like 16:1 at idle. See if that gets rid of the stumble. You've taken a lot of air out of the idle and you may now have too much fuel if you haven't played with the MAF table yet. See what it likes. If it clears up at like 16.5:1 or something like that, then just get that ratio into your MAF table (14.7/16.5 = .89). You want to run leaner at idle. Seems like 16.3:1 or so does pretty good with a cammed setup. Since your STITs are pretty close you can rely on that ratio to clean it up.
You're going to have to log MAF frequency at idle to see what the PCM is looking up at idle.
What you can do is use the bi-directional controls (after you turn off adaptive spark) in the scanner and lean it out to like 16:1 at idle. See if that gets rid of the stumble. You've taken a lot of air out of the idle and you may now have too much fuel if you haven't played with the MAF table yet. See what it likes. If it clears up at like 16.5:1 or something like that, then just get that ratio into your MAF table (14.7/16.5 = .89). You want to run leaner at idle. Seems like 16.3:1 or so does pretty good with a cammed setup. Since your STITs are pretty close you can rely on that ratio to clean it up.
You're going to have to log MAF frequency at idle to see what the PCM is looking up at idle.
Last edited by JakeFusion; 10-04-2014 at 10:27 PM.