IAC Steps and near stalling....

[LS1_Dragster]

How/where do you modify the 'steps' for the IAC? I see airflow in Grams/Sec but how does that get converted to steps?

The problem is 2 fold:

1) After the burnout the idle drops to 500-600 RPM and it take quite a while before the idle gets back to normal. During this time the IAC steps flatlines at 199 then after a while it goes to 240 and the idle is fine. During the time it's flatlined at 199 the timing is also flatlined. Once the IAC steps start moving so does the timing. I have drilled out the hole in the throttle blade yet I have to open up the blade a ton.

2) When it's cold started the idle is lower then commanded. I've played with B4307 and it doesnt seem to help.


Lee

[mr.prick]

have you done RAFIG?

[5.7ute]

As mr.prick has stated you need to go through the rafig procedure to get your desired air dialled in. Once you have done this log your IAC count to see where they are at a warm idle condition. You should be aiming between 40 & 80 steps in this condition. Judging by your high 200 counts you need to open your throttle blade/drill the butterfly to bring the steps into an better controlled area.

[LS1_Dragster]

I havent doen the RAFIG, took me a while wading through all the posts to figure out what your talking about!

I have drilled the hole fairly large and the butterfly is open 5-6 turns over stock.

I'm replacing the stock throttle body with a holley 1000cfm 4150 style throttle body in a few days so I'll worry about the RAFIG then.

Thanks for the help.

Lee

[MICK]

Hay Lee,

Good to see you got to do some skids in the Dragster.

We just had the Australia Winter Nationals here at my local track, I'm all skidded out.

Do you have any pics of your rail.

What's the class regulations that you are running in?

O and that Holley 4 blade does it have the molded boss to run the GM Idle stepper Motor?

You can make something up if you need to, but if it does' nt, the RAFIG and the rest of it will be out the window and you will need to fudge that area in the tune.

Attached is a shot from the deep end of the track at Willowbank, that's where I like to hang out.

Supercharged Door Slamers stole the show with a 5.90 pass from Judd. This set a new world record for all of 2.30 sec after someone in the US ran a 5.89.

Cheers

Mick

[LS1_Dragster]

Hi Mick,

No pictures yet, I have video but no way to convert it at this time :-(

The converter and gears are way wrong. The converter will only come up to 3600 on the T-brake and and the 3.73 gears kill just about every aspect of it! 5900RPM through the traps at 146MPH. The 60 is a scary 1.42 so no bragging here until these get changed out.

My wife did have fun with it though and the fellow racers couldnt stop talking/staring at it! MOST of the racers had no idea what the engine was and when the smoke cleared the majority said it was cool and some said they had been thinking about doing it too.

I suspect that in the future we will see more of these because they are cheap and easy and will run 8.90's with little effort and cash.

No class racing here at our track, just brackets.


Not sure on the Holley but my plan at this time is to get it to idle with the throttle body and only give the computer the ability to add a little air if needed but mainly just relying on the throttle body for idle air. The only time the IAC would be needed in this application is after a burnout.

Lee

[LS1_Dragster]

OK, got the holley throttle body on. The TPS was a direct plug in and works great. I had to reverse the 2 groups of wires going to the IAC because the higher the steps were it actually retracted. Reversed the wires and it works fine.

Now the problem:

when the dragster starts up the data logger show 310 steps, I see this in the tun file as the parked numbers so this is OK, within a few seconds the numbers start going down as expected, so does the RPM but stops at 190. Then after a while the numbers do drop down to 0 then shortly after starts to die. I have to manually keep the idle going then after several seconds the RPM's shoot sky high then settle down.

Will this be fixed with the RAFIG? I havent perfromed this yet because the engine is now hot so I'll wait until tommorow. I just need to know if there is anything else that I can do in the programming in the mean time so I dont waste more time tommorow...

Lee

[5.7ute]

The IAC is meant to retract as the step count gets higher. The 0 steps position is with the pintle of the valve extended against the orifice in the throttle body. As the step count increases the pintle is retracted from the seat, increasing the amount of air that bypasses the throttle blade. You will need to return the wiring back to how it was for the pcm to have any learned control over the idle speed.

[LS1_Dragster]

I explained it wrong! It does work correctly with the wiring reversed.

Lee