HELP, Car dies when breaks are applied!

[GNVenom]

Well, you don't actually "set" the IAC. It is a stepper motor that steps out or in depending on what the commanded idle speed is in the PROM. As long as you're in closed loop, the IAC will adjust the air flow accordingly to control the idle speed. Just as long as the base idle (set by the stop screw) is set properly, the idle will stay consistent. If for some reason the idle doesn't cooperate, you need to look at IAC counts on your scan. That will tell you if the stop screw is correct.

You need to examine the MAF and LV8 values to see if the MAF is the culprit. An out-of-calibration MAF will give you fits when you're dealing with decel enleanment and idle. Have you replaced your O2 sensor? That could play into the fuel ratio.

 

[TurboTerry87gn]

The IAC is just a stepper motor. When the computer commands the motor to move a number of steps it assumes it does so. If it is commanded to move 50 steps in one direction and it lags due to excessive load and only makes say 30 steps the computer still thinks its moved 50 steps. There is no direct feed back from the motor.
I assume the OEM computer re-homes the stepper motor at the intitial key on.

If the motor is missing steps when commanded to move longer distances to "catch to decelerating engine" during idle down or after unloading from a high load, like a burnout the IAC motor might not be able to respond fast enough even if it is commanded to.

On a stock ecu I don't know if there is any thing that cam be done to bandaide the IAC.

On my old FAST system there was the throttle follower that makes the IAC follow the TPS sensor. I had it set so when the TPS sensor was cracked even a little the IAC motor opened pretty far. As the engine idles down the stepper motor had a long way to close so the rpms would settle slow coming off a burn out. The PID loop also controls the speed the IAC motor would respond, so actually lowering the proportial gain would cause the engine to idle down slower.

Hope this give you an IDEA about what is going on as far as the control and IAC motor it self.

 

[GNJoe86]

The maf is a 3.5" with a translator and the O2 sensor is brand new. I have the iac counts with in the 10-40 recomended range. The car has been known to die after the burnout at the track, the iac looked old would replacing it help? where can i get one?

 

[TurboTerry87gn]

I would try to borrow one for testing first.

Have you take the IAC off to look at it. If I remember right there is the body, (housing with about a 1" bore) and the stepper motor (motor with a linear screw shaft spring and big conical valve that seats in the body. You might try cleaning it up with a little carb cleaner or something. It probably has carbon and/or sut in it.

 

[SloGN]

How much gas is in the tank when this happens?. It could be that your gas tank has been replaced with a carbed g-body tank that does not have any baffles in it and @ low fuel levels the fuel is sloshing away from the pump long enuff for the the engine to run out of fuel.

 

[Clark6]

The maf is a 3.5" with a translator and the O2 sensor is brand new. I have the iac counts with in the 10-40 recomended range. The car has been known to die after the burnout at the track, the iac looked old would replacing it help? where can i get one?

mine use to die after every burn out at the track also. . it was my best chip that i ran the quickest time with but it still shut off right after the burn out, my fuel psi was right, it only shut off once at a traffic light but i upped the psi a bit & it quit that but still did it at the track after a burn out, i changed chips and it quit. try another chip.

 

[GNJoe86]

The fuel is below a half tank but my tank does have baffels and the speed was very slow when it dies out recently, it is when I am almost stoped. I already cleaned the IAC and it isnt better so im going to try a new one next. My fuel pressure is at 44psi, I know it is high but thats because of my tune and I hope I dont have to lower it to solve the problem.

 

[BMF_Racing]

The fuel is below a half tank but my tank does have baffels and the speed was very slow when it dies out recently, it is when I am almost stoped. I already cleaned the IAC and it isnt better so im going to try a new one next. My fuel pressure is at 44psi, I know it is high but thats because of my tune and I hope I dont have to lower it to solve the problem.

I am currently having this same problem now with Lacey's car. It will stall after each burnout or if I'm testing the trans-brake out and let out of the throttle it stalls but will idle under normal conditions. I have noticed that it will not stall after a load until it is warmed up (165 to 175degrees) and will not even idle on its own if it gets hot (190 degrees). I was going to chance the IAC, but will take it out to clean it out. It never did this with the stock turbo/TB (it has a dbb6776 and 62mm TB now with the same IAC as old setup). Any ideas?

 

[charlief1]

Great sugestions guys but let's try something different. KISS! Keep it simple stupid. No offence intended. We know what your fp is, have you hooked up a vacum gauge? Have you done an injector blead down test? Start with non computer problems that might cause it and then go to the computer. It almost sounds like a vac leak.

 

[SRGN]

Try shutting off the DFCO(decel fuel cutoff) in the extender chip.

 

[GNVYUS 1]

If the IAC is within the correct range why would you replace it?

Defco was what I was thinking also, look at your BLM's when you hit the brake or let off the gas when cruising, if they plummet that is a big culprit right there.

I always have the chip either at 800rpm or 850rpm for idle to help any drops in the rpm for whatever reason.

Post the Scanmaster data at idle and then what happens to BLM's on decel.

 

[miz]

I had similar problem and it ended up being bad computer.

 

[GNJoe86]

The Dfco turned out to be the problem. Its all good now thanks for your help guys!!

 

[BMF_Racing]

Try shutting off the DFCO(decel fuel cutoff) in the extender chip.

Sorry for being clueless, how do I turn this feature off to see if this is my problem also? I'm very new to the MAFT Pro and chips in General.

Would it make sense that this stalling problem would be worth when the engine temp is higher?

Thanks for the help in advance.

 

[GNJoe86]

It only happens if you have a smaller diameter torque converter, this is because being smaller it doesn't have the same momentum of a larger converter. The car basically over fuels and dies out because of this. The option is set in your chip, I have an extender extreme chip and there is an option to turn this on and off.

 

[SRGN]

Sorry for being clueless, how do I turn this feature off to see if this is my problem also? I'm very new to the MAFT Pro and chips in General.

Would it make sense that this stalling problem would be worth when the engine temp is higher?

Thanks for the help in advance.

Look at the manual that came with your Extender Pro chip. You'll need to set parameter 9 to the appropriate value (if not modifying anything else in this cell, "8" will turn off the DFCO only). PM me if you need more details.

 

[BMF_Racing]

I ran into another issue trying to adjust the DFCO. See below link.

http://www.turbobuick.com/forums/co...g-extender-pro-chip-defaults.html#post1945477


Any help is much appreciated,

Thanks,

Brad