Hey all,

I've noticed that if i do a 3rd gear pull, the airflow looks normal (keeps going up with rpm, although i do have minor dips here and there). However, if I do a log starting in 2nd gear, once I shift to third, airflow will spike and then dip severely. Is that normal? Look below for a log running through 2nd, 3rd, and 4th gears. Note I'm running less boost due to high elevation. Note that WGDCC is 0. Reactive is maxed out at 100%, passive intentionally drops to avoid running too much boost at high elevation. Any thoughts?

Airflow = maroon
Boost = blue
Load divided by 10 = pink

 

Because you are either totally overshooting your boost curve and it is dropping in error correction, or you are naturally following a tooth shaped boost curve and it is creating that shape.

Given the same amount of boost, airflow should continually rise with RPM. Since your boost is dropping (I think, that chart is a bit confusing with boost being so close to the line for load) so will airflow, and the RPMs are not growing "fast enough" to compensate (at least visually when you are viewing it on the graph).

 

BOV leaking on spikes...and slowly closing?

 

I think your BOV is leaking too. See how in 2ng gear your air flow matches your boost. Then in third, your air flow is less. That is because your BOV is recirc and leaking. So you are just re-ingesting air that was already measured.

 

While I don't disagree that the BOV may be leaking, the way it dips lower in third gear suggests to me that error correction over correcting down, then slowly correcting back up. I would think a leaky BOV would present itself as a smoother downward slope (as the leak closed less and less air would leak, not one big gulp and then a close up while the turbine refills the charge piping).

 

Thanks for the ideas guys. Note that WGDCC is 0, meaning no boost error correction. I'm not overboosting or exceeding target loads. If I do a straight third gear pull from 2k rpm's, it doesn't have that dip. Does that still imply BOV leaking? Note that the car is completely stock aside from the tune. Is this normal or something I should address?

Can anyone else do a log in running through the gears (either 2 and 3, or 3 and 4)? I see the same effect after shifting to the next gear. Thanks!

 

Do a boost leak check!

 

Maybe this is a dumb question, but if I had a boost leak, wouldn't this weird airflow behavior show up in a normal 3rd gear log? If I do a full 3rd gear log from 2k rpm's, airflow keeps going up normally. The airflow is only spikes and dips after shifting. Shouldn't a leak show up regardless? I've checked that most of the easily accessible hose clamps to make sure they are tight.

 

I've have noticed since they day I put my wideband on that AFR's always spike every gear shift. I always attributed it to the injectors already spitting fuel into the cylinder and me lifting off the throttle to shift, hence a spike of unburnt fuel hitting the exhaust.