Why does my car consume fuel even when coasting (09 Accord I4 automatic)
 

My car, the 2009 I4 Accord Automatic, consumes fuel from 0.9L/h to 1.4L/h (seems mainly depend on tempereature) no matter if I am parked idling, or coasting at 35mph or coasting at 65mph.

Even if I am coasting, gaining speed on a down slope in gear, it will still consume whatever it consumes when idling.

The car goes to 5th gear at about 35mph, and I can tell that when it is coasting at 5th gear, the RPM stays with speed, which means the engine IS engaged. But it is still consuming fuel!

I thought modern fuel injected engine does not consume fuel when coasting.

This kinda of upsets me because I coast considerably shorter distance in gear, and I can't even rip the benefit of no fuel injected.

Any time the engine is turning its safe to assume the engine is consuming fuel.
The newest engines may cut fuel if you let your foot totally off the gas petal when rolling.

It's always 'running' when the key is 'on'.

The idea behind 'engine on, neutral coasting' is it should consume less gas.

The 2013 BMW 3 series turn off at stops, then restart w/ the press of the gas pedal.

He said AUTOMATIC.

I would never kill the engine with an automatic.

That now goes to the towing instructions. "Engine off, Automatic in neutral" major no-no.

Just the other day, someone said DFCO uses zero fuel, none. It doesn't seem accurate, but I don't know or use it to make it valuable. I would imagine if the engine is on, it is using fuel.

A friend who just got into ecomodding was putting their car in neutral to coast. We discussed why it might be bad, and when we checked with the UG, his vehicle was using >10% more fuel coasting in neutral than drive, but in drive, was still using approximately .50 G/h.

DFCO is triggered by specific conditions n different cars, and doesn't necessarily show on SG or UG.

My 2002 Nissan Sentra had a a primitive DFCO implementation. It had to be >2500 rpm and decelerating in gear, with the TPS at idle position. With the 6 speed transmission, DFCO didn't kick in under 70 mph in he Sentra in top gear. Worse, when it did kick in, it put the ECU in open loop for the next 4 minutes.

My 2006 Scion is a DFCOing fool by comparison. DFCO kicks in with any engine rpm >1500 when in gear with TPS at idle. That means it DFCOs at any speed >35 mph in top gear, and it goes into closed loop immediately after exiting DFCO.

My'88 CRX did just like the Scion described above. My Dakota, though, keeps pouring on the coal under about 3K, which is 70% to redline in the thing, and even then it takes a few seconds for it to do it. I suspect DFCO in the Dakota is for brakes-failed-bringing-the-boat-down-the-mountain situations.

Jayliu - SentraSE-R is right - your gauge (ScanGauge, UltraGauge?) may not be properly configured to show when your engine is in fuel-cut.

Alternatively, you could also try monitoring the Loop status (Open/Closed). You might see that change (from closed to open) when the engine is in fuel cut mode even if the fuel/hour may not.

And I bet if you went on an Accord forum, someone with the factory service manual would be able to detail the exact conditions under which fuel cut occurs. As was said, it's different for different vehicles, and depends on a number of variables.

So, I went over to SubaruForester.org and searched for "DFCO" and the first result was some guy complaining that his wife coasted in neutral to stops, several users agreed that it was a vile and terrible thing to do, and someone calling himself "TheMathGuy" made some pretty good arguments including:

Unsafe? Please show me the results of an independent study showing that the rate of accidents is higher for people driving in neutral. I want data, not speculation about why it might be unsafe. Does it actually cause accidents?

and:

The law:
Yes, there are laws relating to driving in neutral, including in Oregon. However, it's kind of vague.
Firstly, the Oregon law only applies to downgrades. Coasting on flat ground, like gently coasting up to a light because it's red and you're waiting for it to turn green: no problem.
Secondly, the way it's written, technically you're breaking the law every time you shift gears on a downgrade in an MT. Apparently (according to the text), you have to choose your gear before you crest the hill and stay there until you flatten out again, which is ridiculous.

The rest was people trying to refute what he wrote while largely ignoring it and an eventual consensus that arguing with one's wife inevitably resulted in losing the argument. They did talk about DFCO, but nothing useful.

Well, the law is an ass.

"Ere he shall lose an eye for such a trifle... For doing deeds of nature! I'm ashamed. The law is such an ass." (George Chapman in 1654 - Revenge for Honour)

Now ask yourself who makes such laws, and why and how they are made. Also ask whether they are enforceable or not.

“Laws, like sausages, cease to inspire respect in proportion as we know how they are made”