Apparently DFCO has other uses. I got it working properly by analyzing my logs and plugging the right values in (+15kpa on enter and exit MAP). Now my fuel trims are way closer to what they should be because they are not going mysteriously rich on decel. Does this make sense to anyone else that this would happen? My reasoning is that under normal throttle (low vacuum) at x airflow your fuel requirements are different than the same airflow during decel (high vacuum). Just looking at the VE table this makes sense to me, and having DFCO working seems to "mask" the problem. The only place it does not seem to help is -10mph where DFCO is not active...but that is also where proportional idle (if it were enabled) would affect the trims...so that is the next thing I will tinker with since everything else is actually working now. The reason I bothered with getting DFCO working is because the PCM seems to want to dump extra fuel in the engine during decel and this was making my trim spread really high. This seems to have decreased the spread by a considerable amount.

 

I see the opposite. DFCO cause lean 19:1 spike on my ve table

 

I agree with HumpinSS, mine makes a lean spike.

Deceleration
Fuel
Cut
Ooff

 

Your trims go positive in DFCO mode? Mine go to 0. Sometimes the trims spike coming out of DFCO, but not most of the time. Are you sure you got all of your DFCO settings right?

 

I am not sure about the trims since i am using a WB. But i will assume they 0 out when the FTC=DFCO

19:1 is the lean limit on the WB so DFCO is working

 

Your AF ratio should max out lean on DFCO. It cuts the injectors to almost no pulse width.

 

With DFCO enabled, my AFR would spike really lean letting off the gas, anywhere from 16-19AFR in MAP15.

 

Perfectly normal. The key is that your trims stop updating because fuel is cut to a specified (negligible) level.

 

Another - I have the same issue with the car under decel in gear A/F will go to 11:1 and sit there, then get back on the gas it spikes up to 16:1 or so then falls back into place.

is this what you would see as well?

if yes what were all the things to did to eliminate the problem?

 

Yup, depending on the cell I am in ... as much as 6 or 7 on the LTFTs. My DFCO settings are factory stock, I have not touched them yet.

 

That sounds about right. On decel the car was just dumping fuel in because of positive trims. I fixed my DFCO entry and exit MAP to cover up those areas. I suspect that they do that on a stock vehicle as well. I added +15kpa to my entry and exit MAP, and that covered any decel areas (above the MPH threshold of 10MPH, below that and I get the same spikes). I need to do some more logging today, but it made a HUGE impact on those positive trims on decel.

If you have a cam, chances are you need to hit those DFCO MAP values. When I was running MAFless I did not have this problem (which makes sense since the fueling is done by RPM and kpa not just airflow like the MAF...I don't think it is accounting for VE...I think)

 

Chalk me up as another one that saw lean spikes with DFCO enabled.

 

DFCO should read very lean, if any reading at all. On my scanner everything goes to 0 or freezes and injector pulsewidth goes to 0. If i'm decelerating with my foot on the brake, no dfco, i'm slightly rich.

 

Have you tuned your DFCO? It should work when you are pressing the brake...at least that is what I thought...I will have to do some more logging and check.

 

When in DFCO my LTFT goes way lean as well.

 

You shouldn't. The LTFT's are not supposed to update while in DFCO.

 

When I was refering to DFCO lean I mean o2 readings, my LTFT freezes around 0. At low speed with your foot on brake DFCO can't be actve or the motor would die because the TC clutch unlocks when foot is on the brakes.

My DFCO is factory stock but I'm sure it works differently in M6's.

 

I should rephrase…My LTFTs go way positive and my AFR pegs at 19.x on the scan tool and the WB shows 20.7.

John

 

The only time I ever hit DFCO was in the Smoky Moutains, on very steep hills. If I was in 2nd, for example, and the car was still accelerating and the rpms exceeded a certain point, the exhaust note would suddenly change and you can tell more of a load on the engine. It shouldn't just happen when you let off the gas under normal conditions!

 

That is exactly when mine kicks in. If I have the trans in 4th, then they go right to zero for a split moment. If I am in 1st, 2nd, or 3rd I will get very lean when I let off the accelerator at speeds.