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Old 05-15-2009, 05:28 PM   #31 (permalink)
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Originally Posted by PaleMelanesian View Post
That's true during that instant, but when you look at the whole trip, the balance tips the other way. I've tested pulse-and-DFCO against pulse-and-neutral idle and against steady speed driving. The results:

Best: pulse and EOC
Good: pulse and neutral idle glide
Ok: steady speed
Worst: pulse and DFCO

You only want to use DFCO if you're needing to lose speed, like coming up to a red light, or down a mountain. Any other time, it's a net loss in mileage. The drag from engine braking overwhelms the gains from no fuel being used.

My honda does DFCO down to 1200 rpm, and below that it restarts the fuel flow. You can feel a surge when this happens.
o.k. your priority list is probably right, for most cars. The thing that bothers me about pulse and EOC is that it involves a lot of extra cycles on the clutch and transmission. Neither were designed for this use. One has to question whether the added fuel economy is worth the extra wear. Not to me, but that's just one opinion. I suppose that for short competition it makes sense, but not for day-in-day-out activity. I still maintain that method 1 has to impose a fairly heavy wear load.

Incidently, EOC=engine off coasting, DFCO= decelleration fuel cut off, FAS= forced auto stop. Many of these acronyms are defined in the glossary link on:

CleanMPG, An authoritative source on fuel economy and hypermiling

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