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cutlassefi
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Joined: 05/13/2016 - 06:06
4 wire IAC

I've watched the videos repeatedly regarding setting up a GM/Chrysler 4 wire IAC yet I continue to get inconsistancies.

I've enclosed a log to explain what the issue is. I know it will pull timing if the IAC is closed and the target idle speed is still too high. But why would it add timing when the parameters seem to be within range like at the end of this log?

CORY5.itssn

CORY5.itlog

 

AEM_HB
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Joined: 11/07/2016 - 09:22
Target Idle RPM: 925

Target Idle RPM: 925
Actual RPM: 763
Ign Trim table value:5-6 degrees

cutlassefi
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Last seen: 5 hours 44 min ago
Joined: 05/13/2016 - 06:06
So you're saying that it was

So you're saying that it was trying to achieve the target by advancing the timing? If so then why wouldn't it have just opened the IAC more? I saw a total of about 38* when the requested was only 22 or so.

Thanks!!

AEM_SB
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Last seen: 4 hours 57 min ago
Joined: 06/07/2014 - 14:29
The airflow feedback (IdleFB,

The airflow feedback (IdleFB, which changes the Idle Position) and the ignition trims are happening independently of each other. The ignition trim happens quickly, because the engine can respond quickly to ignition timing changes. The airflow trim usually happens more slowly, because there is a bit more delay in the engine's response to IAC position. Allowing big airflow changes quickly tends to result in an engine that hunts up and down without settling to a smooth idle RPM. Later in that log it looks like the IdleFB (airflow feedback) did change because the measured RPM was too far below the target. The ECU won't slowly use less spark timing and add IAC position, because we have to assume that some racers are running simplified setups without an IAC.

By the way, are you aware the numbers from the table 'IgnTrimIdle' and the calculated values from the 'Idle Ignition P/I/D Gain'  and 'Idle Ignition Min/Max' are stacking up?  The table is configured to trim timing by about +/-7 degrees,  and the wizard options are configued to trim timing by about +/-10 degrees, that's a possible +/-17 degrees combined. I think it would be easier to keep track of just one method rather than using both, but the ECU will happily do both trims the way it's currently configured. 

 

Two suggestions that might help prevent the RPM from going below the idle target:

1. Change the option 'Idle FB Deadband-'  in the wizard from -75 to -50 or -25. This will allow airflow feedback to open the IAC further when the measured RPM is just 50 or 25 RPM below the target.

2. Adjust the y-axis breakpoints in the Idle_Decel table (currently 0, -500, -1000, -1500... try 0, -200 , -500, -1000)  and consider using positive numbers to help 'catch' the engine if it's decelerating quickly around 1200 - 1100 - 1000 RPM.

 

Hope that helps,

SB

cutlassefi
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Last seen: 5 hours 44 min ago
Joined: 05/13/2016 - 06:06
Thank you as always. But

Thank you as always. But before I go any further, I've been to your training twice, this was never covered anywhere close to this amount of detail, sorry. This system is so vast and does so much that it would be nice if your training was a bit more intense. I would for one would welcome that. Just sayin.

I lowered the idle min and max and made the changes to the Y axis as well. We'll see how that goes. Again thank you very much.

AEM_SB
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Last seen: 4 hours 57 min ago
Joined: 06/07/2014 - 14:29
It's tricky to squeeze more

It's tricky to squeeze more training into another day or two, scheduling aside I'm guessing it's hard for people to retain two 8-hours days worth of new information in the first place. Hopefully searchable forums and a few youtube demonstrations will help with some of these things. Idle specifically is something that only some customers care about, others are happy blocking off the IAC and adjusting the throttle stop so the engine still runs when it's cold. As another example, our training guys could spend even more time on traction control or boost control but there are also some customers who will never use those functions. If we get enough questions about the same thing we try to double-check the documentation and/or make that topic the next in line for a demonstration video.

Hope that helps,

SB