How does DFCO work in your car?

[dleefoto]

Some people had concerns about heat fluctuations in the engine if certain injectors were killed. I'm interested in any gains from the cut off switch.

[Piwoslaw]

Arragonis - My turbodiesel is the same, engine braking down to 1000rpm or even lower shows 0.00 l/h on the ScanGauge. On the other hand, my Grandma has a Corsa C with the 1l, 3-cyl petrol which I get to drive every few months. I'll try to remember to take my SGII with me next time and check DFCO. I have noticed that engine braking is totally different in that car - tiny engine with smaller compression ratio...

[Arragonis]

Originally Posted by Piwoslaw

Arragonis - My turbodiesel is the same, engine braking down to 1000rpm or even lower shows 0.00 l/h on the ScanGauge. On the other hand, my Grandma has a Corsa C with the 1l, 3-cyl petrol which I get to drive every few months. I'll try to remember to take my SGII with me next time and check DFCO. I have noticed that engine braking is totally different in that car - tiny engine with smaller compression ratio...

This is the thing I am finding tricky. In the TDI the relationship between fuel used and the throttle is linear, well with an effect for engine speed, but more or less - foot down, more fuel, lift off no fuel. As it's fuel controlled that makes sense.

In the small petrol there is less of that relationship, from observation anyway. I am using my DFCO trick more and more though, and hopefully 1st bar on the gauge at 140+...

[TheMarkofPolo]

The DFCO for the Vibe usually works between about 40 and 65 mph, once the engine is at least partially warmed up.

If I have the A/C on, DFCO is a bit more hesitant to engage, and has a range closer to 50-60 mph.

It's very handy on the highways and non-trafficky parts of town.

[busypaws]

If I remember correctly from the SG manual. It does not exactly "read" DFCO. It "assumes" DFCO when RPM is greater then some value and TPS is 9. You really have to feel it in your rear end to see if your going into DFCO. As the RPM coasts down to 1200 or so I can "feel" the injectors start back up because the deceleration "engine breaking" is not as great.

[dennyt]

My '94 Subaru Loyale will do DFCO down to ~2000 RPM depending on what the Idle Air Control (IAC) valve is doing. When I had the IAC unplugged, it would DFCO down to idle at 750rpm, which was awesome. Driveability was terrible though, so I put a restrictor plate on the IAC and plugged it back in. Now it can only bump the idle up to 1100, which is fine by me.

[tjts1]

Rather than describe DFCO I can show you how it works on my car. Below is a screen shot from a megasquirt datalog.
At the top is RPM, TP is throttle position sensor angle, PW is injector pulse width in milliseconds, and at the bottom is air fuel ratio between 10-20 afr.

I took my foot off the gas around 2100rpm. After the TPS closed to below 0.4% it waits 1/2 second before it shuts off the injectors. There is about a second delay between the moment the injectors shut off and the WBO2 sensor recognizes a change in the AFR. I coast down to 1200rpm when the injectors kicked back in. You can see a 2 second delay between the injectors turning back on and any AFR change. Total DFCO time was 15 seconds on a slight down hill from ~30mph to a stop light. You can see where I applied the brake initially when the RPM line bends downward then increased brake pressure before coming to a stop. The recording was done a while a go before I had idle control really nailed down. The RPM is a lot more stable now when I press in the clutch without all the big swings. You can see a quick PW blip to zero when idle RPM jump up above the DFCO trigger point. This is the type of thing you look for to fine tune MS for daily driving.
cheers

[t vago]

My truck enters DFCO on all of the following conditions:

continued coasting in D down a steep (>5% grade) for greater than 20 seconds
the moon has to be exactly at 0.125632 phase
the wind has to blow exactly from the north
there has to be some chicken bones in the bed

Well... maybe some of that is exaggerated.

To date, in 2 years of owning my truck, I think it has entered DFCO exactly 4 times.

[Mustang Dave]

In my Mustang, DFCO only works after the coolant temperature has reached ~150°F. Then it will DFCO down to about 1500 RPM. With cruise control engaged, it will DFCO down to ~1000 RPM. Tapping the cruise control down is a great way to shed speed for a lower speed limit zone.
My (diesel) truck DFCO's anytime my foot is off the accelerator pedal and RPM is above idle RPM.

[rmay635703]

I think I speak for most everyone who has taken the time to look.

DFCO works very poorly when it works on most every vehicle I have driven.

In my cobalt it takes about 5 seconds to engage, it usually only kicks in as my rpms slow through 2000rpms above that and it doesn't usually engage, below and it will only engage after a long wait in 4th & 5th and not for very long.

I think DFCO is really only usefull in situations where you have a long steady hill that you do not want to gain speed on.

My key works much more quickly and effectively than DFCO.