When I go down hill with the truck in gear and the engine holding back the truck speed, why can't the fuel be shut off.
The motor is being run by the transmission, so it doesn't need fuel to turn.
All the accesories should still work if the key is left on and there will be vacum for the power brakes because the motor is turning.
I just don't know how this could be done. Maybe a fuel pump shut off switch?
On a long grade like the Grapevine or coming from Tahoe I think this could save some gas with no real problems. When you want to start up again just turn the fuel back on and the motor is still turnig so it should start right up.
What do you guys think? Am I crazy?
I cannot comment on the mechanical side of doing something like that because it is too early in the morning for me to think properly. I can say that coasting downhill is when I use the least amount of fuel. It's when my Scan Gauge Instant MPG reading says 9999.
Not sure why I or anyone would want to go through the hassle of trying to save fuel during the engines most efficient time of using it.
When I go down hill with the truck in gear and the engine holding back the truck speed, why can't the fuel be shut off.
It already does this. Electronic fuel injection systems have been doing this since the mid 1980's. They just don't fire the injectors, so no fuel goes into the engine.
__________________ Mark
Former Ford automatic transmission engineer, 1988-2007.
It's when my Scan Gauge Instant MPG reading says 9999.
It reads that high because the speedometer shows the Scan Gauge that you're moving, but there is no fuel going into the engine, so you get REALLY high fuel economy.
__________________ Mark
Former Ford automatic transmission engineer, 1988-2007.
I don't think I have ever seen my Scanguage go above 50-something mpg in the F350, and never below .7gph. I've seen 175mpg in the Ranger when it drops to .2gph when coasting, but nothing close to 9999.
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2004 F350 XL CC 4X4 V10 4.30LS purchased from Jeff Clark at Van Bortel Ford Pics
It already does this. Electronic fuel injection systems have been doing this since the mid 1980's. They just don't fire the injectors, so no fuel goes into the engine.
I guess thats why the automotive engineers make the big bucks !!
so it is better for gas usage to leave the truck in gear and when coasting down the hill rather than take it out of gear and let the engine idle.
For a while there I played around with popping the stick to neutral when I was able to coast downhill and still maintain the legal (and then some) speed limit. I can say that with a stick you will save more fuel this way than leaving it in gear and coasting. I netted approx 1.5mpg better fuel economy this way over just leaving the stick in gear, the truck coasts far longer at far greater speeds than when I leave the gear engaged.
Problem was guessing what rpm I should be engaging which gear at what speed when I reached the bottom of the hill so as to not over rev or bog down the engine. In others words, was I saving money on fuel at the expense of the clutch and the timing chain/gears? While I got real good at guessing the correct rpm to have the engine spun up to for the appropriate gear at a given speed to reingage the trans, I stopped this practice as it was way too involved for the improvement I was getting in fuel economy vs the wear and tear I might've been putting my clutch through.
So I'm back to my old driving habits, and still getting the same old reliable 13.5mpg city/hwy combined mileage to/from work.
I can say that with my 4600lb Buick, I coast that puppy down every hill I can, leave it in gear, accelerate slowly when I can, and drive moderately and she still turns in 19.5mpg city/hwy combined mileage to/from work.
OK, I do nail it every now and then when ricers w/ fart pipes and whale tails rev up next to me at a light. Then it's ricer in the rear view, and 14mpg to go along with my grandpa woody wagon woopin up on 'em, ooops, thanks Detroit!
RustyFuryIII
__________________
'96 Buick Roadmaster Estate LTD/CE Station Wagon, 5.7L LT1 detuned Vette motor, 2.93:1 open rear, and factory 5000lb tow package
I don't think I have ever seen my Scanguage go above 50-something mpg in the F350, and never below .7gph. I've seen 175mpg in the Ranger when it drops to .2gph when coasting, but nothing close to 9999.
I'll be more than happy to snap a pic next time it shows it. Maybe it's because I have steep hills (volcanoes) here??
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I had no idea that NO fuel was injected in the engine while coasting downhill! How does the engine know when I'm coasting downhill? How does the PCM know when to shut off the fuel injectors?
How does the engine know when I'm coasting downhill? How does the PCM know when to shut off the fuel injectors?
It's done by calculating engine load. When the engine is at a relatively high RPM with a closed throttle the engine load is very low. The engine is not producing torque, it's being driven by the trans. The PCM can measure the engine load primarily from the air flow, RPM, and throttle position. When it detects this condition for a certain amount of time it shuts off the injectors.
__________________ Mark
Former Ford automatic transmission engineer, 1988-2007.
Mark, I have a small RV,a 1995 460 with E40D, and I usually drop it into 3rd going down long hills so that I don't overheat and crack the rotors(which I have done before). Would that increase engine load and fuel consumption ?
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I started out with nothing. I still have most of it left.
For a while there I played around with popping the stick to neutral when I was able to coast downhill and still maintain the legal (and then some) speed limit. I can say that with a stick you will save more fuel this way than leaving it in gear and coasting. I netted approx 1.5mpg better fuel economy this way over just leaving the stick in gear, the truck coasts far longer at far greater speeds than when I leave the gear engaged.
Problem was guessing what rpm I should be engaging which gear at what speed when I reached the bottom of the hill so as to not over rev or bog down the engine. In others words, was I saving money on fuel at the expense of the clutch and the timing chain/gears? While I got real good at guessing the correct rpm to have the engine spun up to for the appropriate gear at a given speed to reingage the trans, I stopped this practice as it was way too involved for the improvement I was getting in fuel economy vs the wear and tear I might've been putting my clutch through.
So I'm back to my old driving habits, and still getting the same old reliable 13.5mpg city/hwy combined mileage to/from work.
I can say that with my 4600lb Buick, I coast that puppy down every hill I can, leave it in gear, accelerate slowly when I can, and drive moderately and she still turns in 19.5mpg city/hwy combined mileage to/from work.
OK, I do nail it every now and then when ricers w/ fart pipes and whale tails rev up next to me at a light. Then it's ricer in the rear view, and 14mpg to go along with my grandpa woody wagon woopin up on 'em, ooops, thanks Detroit!
RustyFuryIII
Coasting down a hill in neutral must have made quick work of your brakes as well.
__________________
Chris
1994 Mustang GT
1992 Explorer XLT
2000 Expedition EB
[quote=Monsta;6174824]I cannot comment on the mechanical side of doing something like that because it is too early in the morning for me to think properly. I can say that coasting downhill is when I use the least amount of fuel. It's when my Scan Gauge Instant MPG reading says 9999.quote]
Coasting down a hill in neutral must have made quick work of your brakes as well.
Depends on the terrain and traffic. Many hills in my area have long flats at the bottom of the hill where you can coast for a long time and never touch the brakes. Its not worth it to me to pop it out of gear and coast at least with an auto tranny.
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Maybe it's because I have steep hills (volcanoes) here??
How does the engine know when I'm coasting downhill? How does the PCM know when to shut off the fuel injectors?
