Limp mode - On track after quick 3-4 shift

[dennisscars]

Last time on track, during a spirited 3-4 shift it (supercharged 2.0 liter LSJ) went into limp mode, severe chugging (wide lean rich swings) and finally stopped running. Generally after about 3 minutes of ignition off it will return to normal state.

The Air Mass CYL4AIR are usually in the 1.24grams/cyl range but for this it went off the chart at 23.52. My assumption is that during a quick shift the supercharger bypass is slower to respond than the throttle body causing a weird situation with the throttle plate closed but still at high rpm and at max boost upsetting the normal expected operation causing an "oh crap something is wrong" and calling for an "all stop."

Seems like it's failing the MAF and maybe going to the table and the table is all out of sorts and runs poorly enough to eventually fail. Not really sure how this thing resets itself with the ignition off for 3-4 minutes, which is an eternity on the side of a hot track waiting for the tow rope of shame.

It didn't throw any codes, if it would have I may have turned that one off hoping to correct. Seems like before it would throw a throttle position mismatch, hence the vacuum induced throttle plate "stuck" theory.

This only happens with curtain conditions are present, cool dense air, ie lower altitude, cool air temps and on a straight after a hard turn with a super quick 3-4 shift. I'd rather not lazy shift, which I've had to somewhat be sensitive to and shifter is not smooth enough to speed shift at full throttle. Plus this little motor revs so quick it would go through the roof if you missed.

Had a similar problem with a Maggied LS6 under exact same situation except it put you at minimum throttle response and would permanently fail the stepper motor.

Any thoughts on how to correct the LSJ with what we have to work with? Would increasing B0210 Max VE help, if so by how much and what will changing affect downstream?

Thanks
Vid of track day: Link

[dennisscars]

Noticed that the tach went to 325 rpm just preceding this. Shortly after boost and throttle went to 0% for a couple of frames then back to control with rpm's still reading 325. Shortly after all of this the MAF went off the chart.

Tach also reset after it's "rest."

I'll be searching for tach pickup next chance..

[dennisscars]

I guess the crank sensor is a pretty common failure for this motor.

Not sure why it landed on 325 rpm but I was doing some ciphering and since g/cyl = SAE.MAF*30/RPM if you divide by 325 instead of 6,511 rpm you get 22.15 g/cyl instead of expected 1.11, so it wet the bed and eventually died. Somehow it resets itself after some minutes with key off.

So it appears that it's a (intermittent) sensor failure rather something more heinous.

Now it seems there are no sensors in the GM system.

[joecar]

Also, if the CKP sensor is bad, the pulses it reports are now at incorrect intervals which makes the ECM fire the plugs and injectors at the wrong times.