DFCO timing

[maudyZ28]

been reading up alot about making DFCO more accressive to come in 'earlier' when you have a cam. ie i've got the mao set to higher values as i never get DFCO under stock values now.

This has haelped it kick in but engine braking is quite harsh. It have not been said anywhere but can I confirm the theory that as DFCO still injects fuel at the minimum PW that with more timing there should not be as much engine braking? I dont care if car pops (it sounds pretty cool tbh) but just want to stop engine braking begin so harsh that I have to accelerate again back upto speed, thereby negating the point of DFCO saving fuel :)

[macca33]

When I set my DFCO up, I used the stock C4B (VT2 - VY GTS) tune parameters - works well enough for me and doens't overly brake the engine. Your current DFCO setting may be combining with your throttle cracker / follower settings, with the rate of decay in those tables affecting your 'braking.'

cheers

[maudyZ28]

im not sure that its the TF/Tc that are causing too much braking as the car 'auto' cruises as the desired flow is a little high in gear for idle so the car drives itself :S

Some more work to do but will have a mess with timing. cheers

[Sid447]

Maudy,

Which settings do you have in B5916 & 5917?

[maudyZ28]

Maudy,

Which settings do you have in B5916 & 5917?

as stock 1.19 % for TP and 16 km/h to use base spark. In p/n this is 26 (best idle nice and smooth and MAP < 50 @ 900 rpm)
in gear this is 28 deg. (high octane is about same as basespark to blend nicely into drive, there is no bucking transisting to drive)

I do get some surging when slowing down though at low speeds but still using high octane table there

[swingtan]

FYI.

DFCO: Deceleration Fuel Cut Off. IE. Once DFCO is fully active, there is no fuel going into the cylinder. So the timing once into DFCO makes little difference. You can confirm this by checking the WB signal or even looking at the NB voltages.

DFCO should be configured to come in when you want to slow the car down. When entering overdrive down a steep hill or down shifting when coming to a stop are two examples. If you find that it's slowing the car too quickly when just driving around, then you have set your DFCO enable parameters two aggressively and it's activating too early.

If you find the entry into DFCO is too harsh/aggressive, then you want to look at the "ramp in rates" and slow them down. If you find the exiting of DFCO to slow, you need to increase the ramp out rates.

Simon.

[macca_779]

Simon I think it does revert to the min pulse width so not entirely switching the injectors off. That's for ls1's at least anyway.


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[swingtan]

That's interesting. If that's the case though, then the min pulse width would become somewhat critical when changing injectors that have different min-pulse requirements. I guess it'd be pretty easy to confirm by altering the settings and seeing if the AFR's change during DFCO.

In the E38, I see the following occur...


STFT's go to "0" indicating CL fueling control has been disabled (which you would expect).
LTFT's remain active, which I'd expect knowing how the E38 works.
IBPW is measured at a level that I would expect for normal running. IE. If I'm seeing 0.12gm/S of air, I have an indicated IBPW of 1.6mS.
WB O2 reading is 25:1
NB O2 voltage is 0mV
Calculated Intake Valve Temp reduces during DFCO.


So while the scanned data indicates the injectors are still working, the exhaust measurements indicate there is no fuel at all. My understanding is that this is how you would want DFCO to run, as no fuel=no heat. As you say though, it may be different in the LS1, I'd have to find a log with the same PID setup......

Simon

[maudyZ28]

thanks guys, hence after all my reading around I asked the question.

1: If there is some fuel (min pulse width) then surely timing would effect engine braking -> Note stock LS1 is 0* under about 3500 rpm but has 10* above this. So it has (less?) engine braking at higher rpm. If there was no fuel at all then timing wouldn't make a difference so why spark at all??
2: My NB o2 read about 0mv, actually 15 mv (at work so cant check log exactly) , the WB is lean 22.4:1 or higher and STFT did goto zero while in DFCO
3: My issue isn't that the DFCO enables too aggressively it is that it causes way too much slowing so have to get back on throttle. Although my 228/228 cam only has a little overlap, it still doesnt pull vacuum like stock and never hit stock parameters to had no DFCO and super crusie effect. My issue is it either crusies at moment (too much in gear desired air acting like TC) or it's like pressing the brake under DFCO.

[The Alchemist]

Hey mate, the "braking" effect is pretty much controlled bythe throttle cracker settings. the timing bottoms out to what ever you set it at in DCFO so the throttle/ idle air bleed determines the overrun or braking effect depending on how much you set it at .
I like to set my cars speed neutral down a medium grade. This maximises the fuel saving effects. I also set it so it kicks out at 55km/hr just before you hit town via RPM off settings. Hope this helps. Mike