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 :muahaha:

[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.

http://img.photobucket.com/albums/v712/SSbaby/good_VE.jpg

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.

http://img.photobucket.com/albums/v712/SSbaby/bad_VE.jpg

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.

[SSbaby]

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.

The jerkiness, I found, was actually on coastdown or when repeatedly on-off the throttle at around 80km/h in 5th gear. I think if you run too lean at low MAP/rpm (to save fuel), you run the risk of incurring high gear shunting as the mixture transitions between lean and rich. Having less variance between adjacent cells in the VE curve helps to alleaviate the problem, IMO.

[caver]

Thats exactly what I meant. In dfco there is no injection then at the setpoints the injectors suddenly open and you get a jerk. Like I said I have'nt played with this feature but I will look at it on the next car I do.

[oztracktuning]

I have found less throttle follower and it smooths the transition. Look at the DFCO timing tables of lots of different cars and try them out - this effects things also.

Tune the AFRs in closed loop first to get them nearer to 14.7 and then it will smoother.

Also you can adjust the Base Spark table which you may enter initially when you get off the throttle so that it has lower timing and takes less time to transition to DFCO spark.

All these things can be played with to make it smoother.

[SSbaby]

.

Tune the AFRs in closed loop first to get them nearer to 14.7 and then it will smoother.

Also you can adjust the Base Spark table which you may enter initially when you get off the throttle so that it has lower timing and takes less time to transition to DFCO spark.

All these things can be played with to make it smoother.

The first point I agree with - the leaner your VE table, the less impact DFCO has on driveability.

The base spark solution sounds like its worth trying.

Btw, I've raised DFCO enablers so that it only becomes active over 2000rpm in the first 4 gears (instead of 1300rpm). This way I still use DFCO to conserve fuel while cruising at freeway limits in either 5th or 6th gear.

[oztracktuning]

I think the lower the base spark timing the quicker it activates. The injectors wont shut off it seems until timing has decayed to the set amount. So you can speed up activation by having a lower base spark and quicker decay rate.

The timing in DFCO makes a big difference to rate of deceleration and its a balance that can help it stay in DFCO more rapid deceleration due to timing and you see a lower Kpa MAP for longer. But it can feel annoying. You may have to play a lot to get it right - in an auto it stuffs up the moment the converter unlocks - which is each time the brake is touched. So its not that easy to get to be really nice. With an M6 is should be easier and also more effective in saving fuel.

[ScarabEpic22]

Sorry to be a little noobish, but what do DFCOs stand for? I get a little popping in my exhaust coasting down hills and such, and wonder what I could do to stop that. Thanks!

[SSbaby]

DFCO (Deceleration Fuel Cut-Off). It cuts fuel when all DFCO enablers meet user specified thresholds (rpm, MAP, %TPS and VSS).

I hate to start a potential argument but I've found that adjusting the timing has very little influence on shunting caused by enabling DFCO.

I've decided to turn my DFCO off by setting RPM enabler above 2500rpm and setting MAP enabler below 21kPa... this means that these values will never happen - revving the engine above 2500rpm requires more manifold pressure than just 21kPa! ;)

Setting thresholds for DFCO RPM and MAP is the surefire method to alleviate the shunting. Forget playing with DFCO Spark, IMHO.
:notacrook:

[Tordne]

The MAP is actually a less than, not a greater than ;) So your setting of 21 should still be an enabler for DFCO. When you get off the gas if the MAP goes below 21 that enabler condition will be meet.

I am finding that I set the RPM disabler slightly higher so that it is well disengaged before coming to a stop.

From memory I think you were running from a HSV GTS base (which I am as well)? Some of the other Holden/HSV tunes have different spark settings, and also ramp in/out factors. I'm gong to give these a go as well, what have I got to lose :)

[SSbaby]

The MAP is actually a less than, not a greater than ;) So your setting of 21 should still be an enabler for DFCO. When you get off the gas if the MAP goes below 21 that enabler condition will be meet.


Correct. But at 2500rpm it's not that likely I will get under a MAP of 21kPa, even at trailing throttle?

What I perhaps should have done is set the RPM enabler to 7000rpm, that way DFCO will never be enabled.

[Tordne]

Correct. But at 2500rpm it's not that likely I will get under a MAP of 21kPa, even at trailing throttle?

What I perhaps should have done is set the RPM enabler to 7000rpm, that way DFCO will never be enabled.

You might be right. I am still stock cam and find that the MAP actually come up real slow on decel. But, 21 MAP is pretty low :).

The easiest way to disable DFCO is just to set the temp enable for both M^ and normal DFCO in the Parameters to 140*C. That takes car of the rest. That's all I do when I get pissed at DFCO and need a break :)

[oztracktuning]

Tony
I found that throttle follower settings being zerod helped to make DFCO activation smoother.

I think that at above 2500rpm you will go below 21Kpa.

My DFCO settings are
activate 35
disable 31

RPM
enable disable 1400rpm
activate deactivate 1150

Throttle enable 1.2%

above 36mph

Timing is
-1.010742
-1.010742
-1.010742
-1.010742
0.000000
1.010742
1.999512
3.999023
5.998535
7.998047
9.008789
9.008789
9.008789
9.008789
9.008789
9.008789
9.008789
9.008789
9.008789
9.008789
9.008789

ramp out
0.109863
0.153809
0.175781
0.197754
0.197754
0.241699
0.307617
0.395508
0.527344
0.703125
0.769043
0.791016
0.791016
0.791016
0.791016
0.791016
0.791016

ramp in
0.011963
0.011963
0.011963
0.011963
0.011963
0.011963
0.011963
0.011963
0.011963
0.011963
0.011963
0.011963
0.011963
0.011963
0.011963
0.011963
0.011963
0.011963
0.011963
0.011963
0.011963

The Base spark it ramps in from is
about 28 degrees

If it was a M6 it would be nice like this. But since its an A4 with converter - the moment the converter unlocks it all falls apart ! But this is best compromize for my car with it turning on quite well

[SSbaby]

Putting closure to my shunting issues... I discovered that the shunting at cruise was not related to DFCO but more to do with running the VE table too rich. I loaded a base HSV VY GTS VE and DFCO tables and all the driveability issues were resolved. DFCO is turned back on... just as it was on my original tune (which I later believed was perhaps a bit too lean, hence the changes).

It's ironic that I started out with the VY GTS tune... only to make continual changes... and lose my way! :bawl: Btw, I reckon the VY GTS tune is a great base tune for a cammed LS1. :D

[oztracktuning]

Hi Tony
Many workshops start with the VY GTS Tune and build from there.
I have found the VZ LS1 tunes have some good base stuff also. The timing curve is a good starting point for tunes and the VE table looks like it has had a lot more work.

The GTS is the only one to have a cam with significant lift though and its VE table is quite different.

Its sometimes hard to get cars lean enough when off throttle because the injectors cant pulse small enough - this is something i cant get any better using SVO30 injectors. It doesnt want to go richer than the 13s when off the throttle and before DFCO kicks in.

[joecar]

Putting closure to my shunting issues... I discovered that the shunting at cruise was not related to DFCO but more to do with running the VE table too rich. I loaded a base HSV VY GTS VE and DFCO tables and all the driveability issues were resolved. DFCO is turned back on... just as it was on my original tune (which I later believed was perhaps a bit too lean, hence the changes).

It's ironic that I started out with the VY GTS tune... only to make continual changes... and lose my way! :bawl: Btw, I reckon the VY GTS tune is a great base tune for a cammed LS1. :DTony, it's all part of the learning process and it looks like you're doing good. :rockon:
Cheers
Joe
:cheers:

[SSbaby]

I realised today that the plugs on the LHS bank were not plugged in properly - yes I've been driving my car for around 3 months without realising (since fitting the Crane 1.8RR). Popping the plugs back on cured my surging problem. http://ls1-australia.com/forum/images/smiles/wall.gif

And here I was losing faith in my tuning ability... :notacrook: