What is DFCO????

[blue_falcon]

What is DFCO?? I'm obviously very new.

[CatSkynr]

Deceleration Fuel Cutoff

[blue_falcon]

thanks, which tables would I change or is it better left alone?

[Keith@HPTuners]

There is a lot of information about DFCO in the help files.

[99C5R]

Very very fun to play with DFCO. My C5 no longer pops during Decelleration. Not that I care about that, Lots of C5 customers complain though. Going into turns is fun as this provides quite a bit of engine braking.

[Chris@HPTuners]

Most common thing to change here is the entry/exit MAP values. If you have a cam you will have to raise them up a little cos the bigger cam will not generate as much vacuum on decel, and hence trigger the fuel cutoff.

[QUASAR]

What would give the car more engine braking? Taking fuel out I assume right?

To get rid of the popping on deceleration, you would take fuel out right?


For reference, I have left my DFCO tables alone so far. Say I downshift into first and the deceleration of the motor starts at 4000 rpms. As it coasts down, you can notice a change in the engine braking. The car will "jerk" just a bit. And then right before the car somes to a stop it seems like the engine braking goes away.
This is a function of DFCO right? I can change the parameters of this function by adjusting the entry and exit points as well as how much fuel is supplied, correct? Is there any "target" that I shoudl be shooting for, or just getting it to a combination of where I am happy with how the car feels on decel, and saving some fuel for gas milage?

[99C5R]

I have mine set up so that not only does it take out the fuel, the timing drops to 5 advance. I set my personal car up to be rather drastic. When I take my foot off of the gas, I like immediate decel. Kind of like a carburator car did. I am very sure that I am one of very few that likes it that way. Most of it was disabled before I started playing with it.

[blue_falcon]

Mine pops pretty good when I decel after a WOT pass. I've even had it shoot a flame out of my tailpipes during decel. I don't have cats and I have Loudmouth

[Chris@HPTuners]

What would give the car more engine braking? Taking fuel out I assume right?

To get rid of the popping on deceleration, you would take fuel out right?


For reference, I have left my DFCO tables alone so far. Say I downshift into first and the deceleration of the motor starts at 4000 rpms. As it coasts down, you can notice a change in the engine braking. The car will "jerk" just a bit. And then right before the car somes to a stop it seems like the engine braking goes away.
This is a function of DFCO right? I can change the parameters of this function by adjusting the entry and exit points as well as how much fuel is supplied, correct? Is there any "target" that I shoudl be shooting for, or just getting it to a combination of where I am happy with how the car feels on decel, and saving some fuel for gas milage?

DFCO is a fuel cutoff. ie. zero fuel

Engine braking will be greater when in DFCO. There are RPM and MAP exit points for DFCO, that is the jerk you feel when it renables fuel.

Chris...

[QUASAR]

Thanks Chris..

I was asking those questions while at work not looking at HPT. I was looking over the help files last night. Alot of stuff there I will look over it in depth tonight.

Is it safe to say, if a car is popping on decel, it has not gotten into DFCO because the popping is coming from fuel being released into the cylinders?

[Chris@HPTuners]

yeah, if you log your injector pulse widths you will see they go to zero when DFCO kicks in. Also, spark timing will retard as well.

Check your DFCO entry MAP vs BARO tables and then log your MAP values on decel. If they are not lower than the entry limit then DFCO will never enable.

Chris...

[TT_Vert]

Very very fun to play with DFCO. My C5 no longer pops during Decelleration. Not that I care about that, Lots of C5 customers complain though. Going into turns is fun as this provides quite a bit of engine braking.

can you tell me what you changed and what your original DCFO #s were? Id love to get rid of that pop myself.

Dave

[striker]

so what your saying is when the engine goes into dfco its actually cutting off the injectors totally? wow i never realized that the engine isnt running at that point but rather is just rotating due to being in gear? is that a correct assumption?
this is not really any help on the topic but to me this is a pretty interesting idea

[99C5R]

Not completely turning off the injectors, they are just barely on. If I remember correctly, p/w was .5 while in DFCO.

[Dirk_Diggler]

so what your saying is when the engine goes into dfco its actually cutting off the injectors totally? wow i never realized that the engine isnt running at that point but rather is just rotating due to being in gear? is that a correct assumption?
this is not really any help on the topic but to me this is a pretty interesting idea

It pulses at .5 milliseconds which is barely enought gas for anything. The timing also drops to - advance also. Spark and fuel is cut and the engine is just pumpin air at that point

[marc_w]

FWIW, My truck usually crackles when I get out of DFCO by getting on the throttle.... Going in, it's pretty quiet.

[TT_Vert]

can you tell me what you changed and what your original DCFO #s were? Id love to get rid of that pop myself.

[blue_falcon]

TTT

[AnotherUser]

DCFO is a PITA. It is hard to figure out what to set it to on a cammed car.