Inconsistencies with Deceleration Fuel Cut Off

[YHWilliam09]

I'd like to get other people's input on some inconsistencies I've been having with the Deceleration Fuel Cut Off (DFCO). I drive an '09 Liftback Automatic 1.5L.

I have a ScanGaugeII, and I know when my MPG is displayed as 9999 it's in DFCO mode. I've read that it only goes into DFCO mode when the vehicle is engine braking and over a certain RPM.

My issue is that it seems to have a mind of its own when deciding when to switch to DFCO. For instance, when the engine is cold and still heating up, no DFCO. Once the engine is warm, it still won't always go into DFCO even when the RPM is above 1500. Sometimes I can tap the brake pedal, and then it will kick in. Sometimes I can tap the accelerator, and then it will kick in. Sometimes I can downshift to 3rd gear, and then it will kick in. Sometimes it won't kick in to DFCO no matter what I do even though my foot is off the accelerator, and it's engine braking over 1500 RPM.

Does anybody else notice these inconsistencies, or is it just me? I strive to increase my average MPG as much as possible, so it's been a little frustrating trying to figure out this DFCO and when it's supposed to kick in and when it doesn't.

[IllusionX]

I do not have a scangauge, but i'm pretty sure it won't kick in if you are decelerating on a uphill, since your car is decelerating faster than engine can..

[CTScott]

On my 09 AT liftback, DFCO is predictable. Any time I take my foot off the accelerator with the RPMs over 2500, I see DFCO mode. If I leave my foot off and let it coast, I see DFCO stop as soon as I drop below 1000 RPM.

The key though is the 2500 RPM or greater when you release the accelerator. If it is below that it will not kick into DFCO.

[dj92]

Originally Posted by YHWilliam09

For instance, when the engine is cold and still heating up, no DFCO. Once the engine is warm, it still won't always go into DFCO even when the RPM is above 1500.

I can only speak for my 3cyl, but it idles at 1200 RPM when cold and 800 when warmed up.
I have not really looked after the DFCO operation up to now as I generally push the accelerator just as far and often as needed, but I think this is because the engine needs higher RPM when cold to run smooth and the fuel consumption is increased in order to warm up faster.

[YHWilliam09]

Originally Posted by IllusionX

I do not have a scangauge, but i'm pretty sure it won't kick in if you are decelerating on a uphill, since your car is decelerating faster than engine can..

I think this depends on your speed and how steep the hill is. DFCO will kick in for me sometimes on a gradual uphill.

[YHWilliam09]

Originally Posted by CTScott

The key though is the 2500 RPM or greater when you release the accelerator. If it is below that it will not kick into DFCO.

In my case, this is not true. Today I had DFCO kick in at 900 RPM one time. If DFCO is based on being above a certain RPM, my car doesn't follow the rule. Either way, I'm pretty sure DFCO works quite consistently at RPMs below 2500.

[Kaotic Lazagna]

I have an '07 manual transmission. My DFCO won't always kick in if I'm above 65 mph. Other than that, it will usually kick in. no matter what RPM or gear I'm in.

[Dark Paw]

How does one know when it has kicked in without a scanguage or some other such device?

[trunkout]

this all sounds about normal for our automatic slushbox transmissions!

[why?]

Originally Posted by Dark Paw

How does one know when it has kicked in without a scanguage or some other such device?

You really don't. Sometimes If you are really paying attention you can feel it go off at around 1100 rpms, but you can't feel it go on.

[mirapatec]

I can always expect particular areas of roadways to have this effect kick in. Almost like clockwork, they happen. This is with a daily commute, so it is expected.