I'm not a huge fan of DFCO

[SSbaby]

I know it helps to conserve fuel but I have mine enabled at 2300rpm and 42 MAP.

I recently played around with different VE tables (as I always do) but I find that the richer my VE table, the worse the shunting (surging) due to DFCO being set too low (mixture transitions b/w 12-18 AFR at part-to-closed throttle). I place great priority on driveablility... the slightest shunting peaves me, no end.

What values have people set their DFCO to (without having experienced the slightest of shunting)?

[dfe1]

I've found that spark has a major influence on surging while in DFCO. Note that the description under DFCO spark is not entirely correct. The number in B3336 pertains to the point at which DFCO becomes active. The actual spark setting while in DFCO is controlled by B5915. The values in this table are generally negative and switching to 0 or positive values helps reduce or eliminate surging. Of course, being in the Southern Hemisphere, the reverse coriolis effect may aller the interaction of the fuel molecules, so you may need to have the engine rotate in the opposite direction to compensate.

[Tordne]

Good timing for this thread SSBaby

I have been playing with DFCO quite a bit the last few days as well.

Things that I am trying to get nailed are:
1) When DFCO enables and disables I get popping sounds in the exhaust.
2) When DFCO disables while rolling to a stop the disengage is quite jerky. I have been playing with the RPM and MAP disable points and have not yet found the "sweet spot".

DFE. Interesting what you are saying about the DFCO spark tables. I have been looking at the logs and often I have been at a loss o determine which DFCO disabler has actually been hit. Now I can go check out the spark stuff as well (more).

Cheers,

[dfe1]

DFE. Interesting what you are saying about the DFCO spark tables. I have been looking at the logs and often I have been at a loss to determine which DFCO disabler has actually been hit. Now I can go check out the spark stuff as well (more).

Cheers,

It's interesting to note the vehicle to vehicle differences in DFCO function. The stock setting in my Silverado ramped spark out at a very slow rate. By the time DFCO was activated, it would normally be about the time you were getting back on the throttle. On the other hand, my C5 had a relatively quick ramp so it got into DFCO a lot quicker. I got pretty aggressive with the settings in both, and now I'm in DFCO almost immediately when I back off the throttle if vehicle speed is above the enable setting. I do get a little surging with the Silverado which goes to 0 degrees in DFCO, but not with the C5, which goes to 5 degrees. If you look at a log, you'll probably see that timing is usually the last enabler reached going into DFCO and MAP is the first disabler met coming out.

[GMPX]

I don't like the way it ramps out either, but I am often reminded how small that problem is when visiting the pump!

Cheers,
Ross

[Tordne]

The disengage probably isn't as noticeable on an auto is it? It can be quite abrupt on a M6.

It is generally only noticeable as you are coasting to a complete stop in gear. I can't decide if I should lower or raise the enablers to make it disengage while at a higher speed/rpm etc.

Any advice?

Cheers,

[caver]

I think the problem with the jerkiness is the sudden start of fuel injection.
I havent played with it at all but maybe a table to ramp in fuel injection?

On all the standalones I have done blending in the start of injection has worked wonders.

[ringram]

Yeah I find my goes jerky coming to a stop in 6th gear too

[dfe1]

Sounds like you have your disablers set too low. I haven't noticed any surging coming out of DFCO with either M6 or A4, but I have DFCO disable when rpm drops to 1200 rpm, so spark and fuel are back on well before the vehicle comes to a stop.

[SSbaby]

Actually, I found that if I load my original VE curve I can get away with using low DFCO settings - enable @ 21 kPa, disable @ 25kPa.



However, if I use a 'Tahoe' like VE curve, which has more contours than my original VE especially at low MAP, the DFCO settings need to be raised much higher.



I'm guessing that you need to have consistent AFRs across your VE table in order to get your DFCO settings as low as possible, without incurring the dreaded shunting.