need help with race logs

[04snake]

Last Fall I was seeing some erratic behavior when making drag passes. It was pointed out to me I was getting some EVAP purge during the episodes, well that is out of the equation now yet I am still seeing flat gears with the Dynamic Air calc deviating from the MAF freq so fuel is pulled and I go 1/2 point lean and the car noses over. Sometimes it switches back and forth mid gear. I did some drivability tuning on the VE tables with the MAF unplugged but not at WOT because I got the MAF xfr curve working great but I am thinking for what ever reason, it is using the VE to some extent when everything goes wacky. I believe the KR is a symptom, a reaction of my 12.9 AFR leaning out to 13.4, not the cause because I can get that on passes where the gear pulls look normal.

Here are logs from last weekend. both passes have 4th completely flat after going 1/2 point lean (ignore the AFR, the wide band is not hooked up, but I saw this enough times last fall to be able to predict the AFR direction when this is happening), one of them also has the bad behavior for 1/2 of 2nd gear too.


I added to the VE table up top and will see if that makes a difference the next time at the track. I am open to any other ideas because trying to bracket race a car that can vary 2 tenths sucks the big one. cutting double O lights is a waste when the car is not consistent. Thanks in advance.

- stu

[EC_Tune]

Biggest thing I noticed was the Dynamic Cylinder Air/MAF was lower in 4th across the board. If the PCM thinks there's less air, you get less fuel and more spark.

Dynamic Airflow is a combination of VE & MAF. MAF has less filtering on it than the Dynamic Airflow. (C6 Vettes report unfiltered MAF so things really jump around...)

[04snake]

Biggest thing I noticed was the Dynamic Cylinder Air/MAF was lower in 4th across the board. If the PCM thinks there's less air, you get less fuel and more spark.

Dynamic Airflow is a combination of VE & MAF. MAF has less filtering on it than the Dynamic Airflow. (C6 Vettes report unfiltered MAF so things really jump around...)

The MAF seems to be dead on so it must be the VE side of the combination that is off right? I added to both the VE tables up top around 80+MAP and 4000rpm where the factory tables seem to flatten off but I must still be using, that is what I should have done right? I would take a MAF only tune anyday, that is what I do with my Ford and it is as consistient as a carb motor, but I am struggling with this GM system.

Thanks for the come back.

[EC_Tune]

It looked to me like the MAF values dropped off as well compared to 1st - 3rd. If you have a 1bar MAP sensor laying around, wire it into the EIO and see what the MAP is prior to the throttle body.
Seems like something wierd is happening to the engine's airflow when you hit 4th.

BTW: I would log less stuff for WOT runs. LTFT's are irrelevant at WOT as well as STFT's. If you keep the Byte Count to 24 or less you will get higher resolution data.