Air flow question

I have a slight 'conceptual' question. In tables like the throttle follower and throttle cracker, the values are for airflow. What really is "airflow". In other words does this table tell the PCM what the airflow should be for the given condition and the PCM applies the applicable fuel? Or does this actually add 'x' amount of airflow using the throttle blade (I have a vette) or throttle follower (for cable drive throttle bodies)? Just wondering if I'm basically changing the fuel even though it's called 'airflow'.

Thanks,
Derrick

Its called airflow cause you are telling the ecu how much air to let into the engine at idle.
Fuelling is handled by the VE table and MAF sensor.

So my car goes lean when it tap the throttle. Does that mean I should make the throttle cracker and throttle follower tables smaller?

Also, I'm having a pretty bad hunting at idle and the car is dying sometimes at idle as well. It will hunt between 400 and 1400 RPM. Any ideas what I can do to fix this? I tried increasing idle airflow, but that just makes the RPM go higher when I tap the throttle.

Derrick

Can you post a screen shot of your Desired Airflow table?

427 C5R, nice job! :master:

Are you using the MAF? Sometimes its known for slower response than SD mode.

Quote:

Originally Posted by tazinhawaii

I have a slight 'conceptual' question. In tables like the throttle follower and throttle cracker, the values are for airflow. What really is "airflow". In other words does this table tell the PCM what the airflow should be for the given condition and the PCM applies the applicable fuel? Or does this actually add 'x' amount of airflow using the throttle blade (I have a vette) or throttle follower (for cable drive throttle bodies)? Just wondering if I'm basically changing the fuel even though it's called 'airflow'.

Thanks,
Derrick

Desired airflow tells the PCM the volume of air it needs to let in to maintain idle conditions. On f-bodies (non-ETC cars), we have an IAC valve with an effective area. As the valve opens 'x' number of steps, there are values referenced in a table that represent the volume of air being allowed into the motor. Since you don't have this (from what I understand about ETC cars), there's a conversion done that translates our IAC effective area into TP% for your car. It really has nothing to do with fueling and it's not an exact parameter because there are idle trims just as there are fuel trims. If idle is too low or too high, the trims are added to or subtracted from the desired airflow to maintain appropriate idle. This is viewed in the scanner with the RAFPN and RAFIG pids.

Quote:

Originally Posted by tazinhawaii

So my car goes lean when it tap the throttle. Does that mean I should make the throttle cracker and throttle follower tables smaller?

Also, I'm having a pretty bad hunting at idle and the car is dying sometimes at idle as well. It will hunt between 400 and 1400 RPM. Any ideas what I can do to fix this? I tried increasing idle airflow, but that just makes the RPM go higher when I tap the throttle.

Derrick

Mine goes lean for a split second too when I introduce a significant change in airflow. But, it's for less than half a second. I believe this is not something we can change due to the inherent lag in the PCM. Figure it has to read the change in airflow, then calculate the new required fueling, apply those changes to the injectors...and all this is in milliseconds...then the fuel needs to go through the combustion process, which is finally read by your O2 sensor. To say you'll instantaneously see a richer AFR when airflow is inconsistent is unreasonable if you ask me. But if it takes more than a second, then you need to check your fueling parameters (MAF, VE, PE enable, etc.).

As for the hunting idle, I'd be willing to bet you can correct that with the tables bellow. The following changes were made for my friend's TSP Torquer cam'd car:

B4512 "Filtered RPM Airflow Correction" - (removed 25%)
B4515 "Direct Airflow Correction" - (removed 20% from 0-450rpm)
B5935 "Idle Overspeed Error" - (Removed .5* from 25-250rpm)
B5936 "Idle Underspeed Error" - (removed .5* from 25-100rpm & added .5* to 150rpm and 175rpm)

Tweak your desired airflow and then play with these tables for your specific application. I got it pretty close with these fairly easily. Now, I just have to see if I can get it to quit stalling at full lock left/right with the steering wheel.