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Here's the situation: My commute starts at the top of a hill. I start in my parking space, use a little engine power to exit, then it's ~150' of gentle downhill coasting to a quick stop & left turn (which is blind so I do take a moment for an extra traffic check). Then it's just a quick boost in first gear to get the car rolling followed by several hundred feet of elevation loss over something like 1/2 mile. It's steep! My question is, how would you manage the descent?

So far I have had success letting the car gain its own speed up to ~30mph and then putting it in 4th to engine-brake down the hill. Mind you the car is still in warm-up mode, and the ScanGauge reports the normal idling fuel flow rate of 0.3GPH as long as it's turning at >1500RPM. (Keep in mind that I've never, ever seen the ScanGauge report closed injectors. The lowest fuel flow rate is 0.2GPH from 1100-1500RPM at closed throttle with a fully warm engine.) Some brake application is necessary to keep speed reasonable but the engine does enough of the work to prevent riding them the whole way. Sadly, there is a stop sign and another left turn at the bottom of the hill (though it is followed by an excellent FAS&coast opportunity).

What do you guys think? It seems like a waste to burn fuel down the hill, but it wouldn't do much good to key off and cook my rotors and pads, either.

(BTW, PR of 47.7mpg on the way in this morning. The truth is I'm just greedy and need help gunning for 50 ;) )

If you are handy at wiring, I have an idea for you. I did this on my Saturn and it works great for long/steep downhill grades; also for everday FASing. I spliced into my fuel injector wiring and installed a 5-pin relay. The rest of this will be on the assumption that Honda does things similar to Saturn. There is a common wire to all of the injectors that supplies power to them. The ECU only switches the ground. I cut all of the power wires to the injectors and combined them. I then hooked the wires to the pin on the normally closed side of the relay. Then, you hook all of the wires coming from the injectors(which are now the "cold" side) to the other normally closed pin of the relay. At this point the car will still run normally. You then take a wire from the "hot side of the injector power wires and run it to one of the pins that actuates the relay. You then take a wire from the other pin on the power side of the relay inside the cabin to a switch and run a wire from the switch to a good ground. When the switch is activated, the relay switches to the other contact and the injectors shut off and the engine dies immediately. This comes in handy for steep downhill grades since you can use the killed engine to scrub off speed and still have the key on so mileage is being accumulated. When I visited a friend in PA a couple of times this spring I did this on a 3 mile 20% downhill grade and the really cool thing was that since the key was on, I still had my alternator, power brakes, and A/C if I had needed it.

Brick,
I doubt that you are actually injecting fuel during engine braking conditions. Others have reported that thier scangauge never shows zero when the engine should be in fuel cut mode. I would use engine braking and let the SG think you are using fuel. It has gotta be a SG bug.

Brick,
I doubt that you are actually injecting fuel during engine braking conditions. Others have reported that thier scangauge never shows zero when the engine should be in fuel cut mode. I would use engine braking and let the SG think you are using fuel. It has gotta be a SG bug.

I'm not real familiar with Honda's, but I think they DO cut fuel. My Saturn however slowed down noticeably more when I went from just letting off the gas in 4th to also cutting the injectors. As for the SG, mine reads .1 gph even when I'm in the middle of an FAS. Odd.

I really need to figure that out once and for all. Some kind of simple indicator that taps into the FI circuitry to tell me when the injectors are pulsing would do the trick.

Perhaps an LED inline with one of the injectors?

Brick it sounds to me like you are doing exactly what can be done for fuel efficiency.

The main reason I say that is because you're starting off with a cold engine and those hills are creating a negative engine load- just perfect for warmup. The hills are keeping your parts spinning...not the fuel....and tossing in a tiny part of fuel to heat things up for when the load begins.

I can't think of any better way to drive on a cold engine.
-Steve

I made a super-simple injection light for the Prius a while ago,
written up at http://techno-fandom.org/~hobbit/cars/squirt/ which
I just updated slightly for better spike-suppression. Via
this I 100% knew that NO injection was happening during warp-stealth,
and yet people with Scangauges were reporting some small token
fuel flow so at that point I knew the SG was lying.
.
Sounds like an injector-cut is one of the simplest but most
effective hacks a non-hybrid MPG fiend can install. And even
some of the hybrid owners, i.e. one evidently makes life much
easier with an Insight. No real need in a Prius, and it would
probably throw every DTC in the book if it realized it wasn't
running normally...
.
_H*