Deceleration Fuel Cut Off

[RustNTrucks]

Hello,

As new in HpTuners world I downloaded my factory tune and start to read to try to understand many things.

I found the DFCO parameters and there is something I don't understand :

IMG_2727.jpg

when I see that table, I understand that Fuel will NOT cut off under 2304 rpm . But this isn't what happen when I drive.
After a Cuting Off, the Fuel injection come back around 1100 rpm , not 2300 ...

Can you explain me ?

Also my plan is to deactivate the DFCO when I'll have an unlocked PCM, someone already did it ?

Thanks for your help. ( and sorry if my English is not perfect )
Kind regards.

David. (France)

[smokeshow]

More than likely what you're looking at is the refueling RPM when your vehicle is decelerating with an unlocked converter. The refueling RPM with a locked converter is always lower; that's likely what you're seeing. It just may not be defined in HP Tuners.

[RustNTrucks]

Thanks for your very interesting answer.

Do you know if " ENABLE ECT " parameter is use in both case ( Locked and unlocked converter ) ?
If it does, I guess that put a over range value ( like 110?c ) will deactivate DFCO .


I definitely hate how my truck is braking hard on engine .. Also when DFCO is on and I put my foot back to the pedal I can feel a surge and even sometimes a click from the transmission..

David.

[smokeshow]

Yeah, it should be the same temperature. Is your vehicle modified? That bump on tip-in is called lash cross and should be calibratable, if HPT has the variables. When you get back on the pedal, the throttle comes in first and then spark follows right behind to smooth out the transition. If the throttle and spark aren't coordinated on the tip-in, it can surge torque back into the transmission.

[RustNTrucks]

My truck isn't modified but a flowmaster exhaust.

Thanks for this explanations . The bump is a bit smooth when MDS is activated, probably because only 4 injectors come back in the first time.


Change ENABLE ECT value will be my first test when I'll have my new unlocked PCM.

[spoolboy]

I have played with some of those settings and the RPM settings don't make any change for me. But raising the VSS speed up a bit definitely helped. Mine were set the same as yours. I raised them to what would be 32 and 28kmh. 20/18mph and things were much improved. This is a setting I have seen in many other factory calibrations.

To disable, set it to max temp. But you might not actually like that....

[RustNTrucks]

Thank you spoolboy for the answer.

Did you play with this for the same reason I want to ?

Did you try to disable ? Why didn?t you like ?

David.

[spoolboy]

I raised mine up because of a clunk when fueling came back in while rolling to a stop.

I didn't try disabling it in this particular instance, but I have done it before and had issues with returning to idle and also problems from the catalyst protection strategy.

A lot of guys play with the DFCO when building burble/crackle tunes.

[RustNTrucks]

Ok

I don?t looking for playing or get hp on my truck but only solve this bump problem.

I can?t support this anymore

[spoolboy]

Let me know how you like it with VSS raised.

[RustNTrucks]

Let me know how you like it with VSS raised.

Sorry for my very late answer. I was delayed in my projet because I try to buy some spare PCM to unlock by hptuners. Unfortunately both were bad so I had to buy a new one.
It will arrive in France soon, and I'll be able to test this.

I'll let you know as soon as I tried.

David.

[RustNTrucks]

I received today the unlocked PCM and installed it.
I desactivated MDS and raised VSS speed with values you gave me.

Tryed only a few dozen of miles but it seems really better !

Many thanks 😊

[eboch]

Dont mean to hijack this thread ... but I have an extended/related question. I'm running an LS3 swap (E38ECU). The engine came out of an automatic corvette and the E38 ECU is from the same car, but its now hooked up to a Tremec 5spd. the ECU has no VSS info and the LS3 is not running bank2 O2 sensors or CATs. When I decelerate, I get popping/burbling in the exhaust .... mild misfiring .... I'd like to get rid of that. I think (?) this can be done by adjusting the fuel cuttoff on deceleration. here is what my ECu programming shows under "Deceleration Fuel Cutoff"

Enable ECT: -30 oC
Disable ECT: -35oC
Enable RPM: 1200 rpm
Disable RPM: 1200 rpm

Any guidance on this?

Thanks
eboch