Spark timing dropping at low cylinder airmass - 2013 ctsv

[Maxim]

I have noticed that the spark timing drops from 12-13 to 5 then goes back up and it makes the car lunge forward slightly when the converter is locked.
When the converter is unlocked the rpms will drop and then rise back up.

I have tried to increase the min spark at those cylinder airmass levels as my tuner suggested, but it has not worked.

How can I fix this?

wotlog2.hpl newsparkdrop (1).hpl Tune#7.hpt

The spark drop happens on decel on the highway at around 70mph and it will stop once my speed decreases.

[smokeshow]

Its jumping in and out of DFCO and battling the lockup torque management because of that pops and bangz thing you got going on there in the coastdown spark.

[Maxim]

Would I correct it by putting stock values in the "coastdown" under "idle spark advance"? I noticed those values are reduced compared to a stock ctsv file

I never asked for a burble tune on the car so I'm not sure why its like that.

[smokeshow]

That would be a good place to start.

[Maxim]

So I put that table back to stock and nothing changed. I also made sure every DCFO parameter should be triggering DFCO and it is but the issue is still there.

When DFCO enables at lower speeds 40-50mph the STFT gets super lean then DFCO disables, re-enables, gets super lean, and disables (at 03:30 in dfcobs log). This cycle continues until I slow down.

When I let off at 80ish in the "DFCO3" log DFCO turns on and everything is fine (at 6:56 in the log) until I tapped the throttle at 64mph and it starts the on/off cycle again.

I also see the Tourqe Mgt Advance spark increasing and then decreasing when all this happens at the lower speeds. It also has small dips (-0.4 of spark) in the "DFCO3" log at 6:56 at higher speeds.

How can I fix this?

Normal toon.hpt
DFCO3.hpl
dfcobs2.hpl
dfco bs.hpl

I also just realized I put this in the diesel thread - my bad it's a 2013 ctsv on ethanol/91

[smokeshow]

Why is the DFCO entry criteria so liberal? Those need to be adjusted so that once it exits DFCO, it stays out, unless conditions allow fuel cut again. At low RPM, the entry criteria must be more strict to prevent DFCO re-entry. Set RPM thresholds back up to stock and definitely reduce the TPS entry at 1000RPM and below to zero. There's no reasonable case for having fuel disabled that close to idle speed.

[Maxim]

I put the rpm limits back to stock and changed what you suggested. DFCO is still going on/off.

It happens toward the end of the log.

DFCO test.hpt
dfco4.hpl

I have played with the settings for a while and tried so many combinations, could there be some underlying fuel table or spark table fighting the DFCO?

[smokeshow]

This file is full of surprises... So best practice is to ensure that while in DFCO, there is torque supplied to the crank from the transmission. If the converter is unlocked, particularly with a loose one, that's going to be way more difficult...the engine has little to nothing to keep it spinning, so its gonna try to stall. RPM drops, DFCO exits, spark and fuel ramp back in and it revs up enough to enter DFCO again. If you have the converter locked, this won't happen. Throw in some stock lockup schedule settings and give it a try.

Don't forget to put the idle spark back up in the decel range as well... Those tables need to look a lot like the main spark around 2000RPM and up.

[Maxim]

The coast down spark is stock. Is that what you meant?

I went out to test it, and now DFCO basically doesn't turn on. It turns on after the pull I did, but then after I get on the gas at 11:00 and let off, it never comes back on. It also did this at 06:12:800, where I was cruising and let off, and DFCO didn't turn on.

I think it's probably something to do with the cylinder airmass since it does not go below 0.13 when I let off. It only gets below 0.13 after the pull, and that's when DFCO turns on.

Normal tune.hpt
NormalTest1.hpl