LSA Lean during PE transition

[Meister]

I was working on a car the other day (ZL1) and noticed that it goes very lean on tip when the motor transitions from the open loop table to the PE table (regardless of going WOT, light throttle modulation, etc). On occasion, the MAF and reported airflow will also drop. After looking through some logs I have noticed it does this stock on all LSA motors/calibrations.

Standard changes for PE delays, ramp in, etc have been tested and changed. Anyone else run into this?

[J.Abbott]

Paul,
I have seen this before and the first time I racked my brain trying to figure out how to fix it. I saw it in the scope and after all the changes I made it really did not make any difference. I then saw the time frame that it was happening and it was a hundredth of a second. As long as your delay is similar I don't think you can change it. It is a transition time in the ECU and you have your delays in PE that take effect. Everything takes some amount of time and I believe that is what you are seeing if you are only seeing this in the scope.

[Meister]

Paul,
I have seen this before and the first time I racked my brain trying to figure out how to fix it. I saw it in the scope and after all the changes I made it really did not make any difference. I then saw the time frame that it was happening and it was a hundredth of a second. As long as your delay is similar I don't think you can change it. It is a transition time in the ECU and you have your delays in PE that take effect. Everything takes some amount of time and I believe that is what you are seeing if you are only seeing this in the scope.

Thanks for the response. It is not a standard PE delay timer as those are turned off, it is not the ramp in fuel as that happens instantly and this is not something I have seen on non factory S/C Camaro's or Corvettes but seems to happen with the LSA motor and I will confirm some LS9 logs shortly....time to time I was able to have it occur where it feels like the motor completely shuts down....no fuel, spark cuts out, etc. Something is going on with this

[J.Abbott]

I will go back and look at the caddy file I have, but I don't recall anything irregular with it. What I was talking about above you could not feel, didn't even see it in the histograms since those are all avg's but I was looking in the scope and saw the spike and was spent an hour or two trying to get it out when I realized that it was so minimal that there was really not much I was going to be able to do. Good Luck.

[Meister]

I will go back and look at the caddy file I have, but I don't recall anything irregular with it. What I was talking about above you could not feel, didn't even see it in the histograms since those are all avg's but I was looking in the scope and saw the spike and was spent an hour or two trying to get it out when I realized that it was so minimal that there was really not much I was going to be able to do. Good Luck.

Some of my other vehicles were minimal but this was significant and that is why I noticed it

[joecar]

On throttle tip in, throttle is moving, air flowrate is changing, so this would be transient air, so VE/VVE would also come into play...?

Also, during throttle tip in (or any transient situation), any incorrectness in the dynamic fueling (wall wetting/evaporation) model would show up.

The fact that you're seeing this on OEM supercharged applications makes me think that dynamic fueling is wrong (but only the OEM has the resources to populate those tables).

Does this condition stop as soon as the throttle becomes steady, or does it continue on...?

[Meister]

Joecar, this occurs right when the fueling mode changes from Open Loop steady state to PE (1.0 to commanded PE). If still in PE mode (throttle/other conditions are not met to exit PE) you can do any type of throttle condition and it will not occur. If you are at 28% APP and PE comes in at 30% APP the second it transitions into PE mode it goes lean (about 8-13%) from commanded even if you keep throttle steady.

This occurs in blended SD/MAF (factory) or even MAF only mode. I will upload some logs

[joecar]

Hmmm, so it only happens on going from OL to PE.

[Meister]

Hmmm, so it only happens on going from OL to PE.

Correct

[swingtan]

post logs......

Don't forget that if the WB is some distance from the heads, there will be a delay between the commanded AFR and the measured exhaust AFR.


Simon.