No fuel usage when off the throttle?
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From: N
No fuel usage when off the throttle?
I was talking with a friend today that explained how NO FUEL is used when a car is rolling to a stop at some high rpm. Inertia keeps the engine turning but on fuel injected cars, the computer lets no fuel get burned and thus you end up with better fuel economy than stuffing the car in neutral and coasting.
Once the revs slow to 1000rpm or so, the idle system kicks in and the car uses whatever fuel it normally does for idling.
I don't think this is true, as there's still all that exhaust noise that's still present, created from the combustion process during this situation.
He won't stray from his theory, but can anyone give me a good argument to put an end to this?
///Robin
Once the revs slow to 1000rpm or so, the idle system kicks in and the car uses whatever fuel it normally does for idling.
I don't think this is true, as there's still all that exhaust noise that's still present, created from the combustion process during this situation.
He won't stray from his theory, but can anyone give me a good argument to put an end to this?
///Robin
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From: Redondo Beach
Actually nearly all modern fuel-injected cars simply cut fuel when "coasting down" while in gear. Thus you are not only using less fuel when coasting down than if you shifted to neutral and let the engine fall to idle -- you are actually experiencing a brief period of infinite fuel mileage! 
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From: Vegas baby!!
^ this may be the case, but u can sure coast a heck of a lot farther by having it in neutral. not sure how the numbers work out, but for me, if I'm approaching a red light, I'm coasting and trying to maintain my momentum so if it turns green by the time I get there, I can just put it in the appropriate gear and go from there, rather than having to get back the inertia that was lost due to engine braking.
$.02
by the way, congrats on the newest addition to your family, twohoos!
$.02
by the way, congrats on the newest addition to your family, twohoos!
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From: Saint Augustine, FL
My old boss had a fuel consumption feature in his on-board computer. I think it was an Audi. Every time he did an engine break to a red light, his fuel calculations would go thru the roof (infinite mileage - like twohoos said).
I almost always use this technique, and have had this question in the back of my head for a long time.
Thanx for reminding me.
Anyone else support the fuel cutoff theory?
I almost always use this technique, and have had this question in the back of my head for a long time.
Thanx for reminding me.
Anyone else support the fuel cutoff theory?
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I have an A/F gauge and although it's not a really good one like a wide band unit, I've noticed that whenever I in "engine decel" mode, the gauge is off the scale on the lean side. So does that mean there is no fuel being used. Not sure, but interesting anyway. While at idle, the gauge fluctuates between lean and rich the whole time unless it's going through a cold idle. Then it's rich.
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From: Santa Cruz, CA
I have a FJO wideband O2 and i can confirm that yes indeed the engine goes very lean during no throttle engine braking. The FJO indicates > 20:1 AFR.
xviper, The FJO indicates an average of 14.7 during normal idle. This usually fluctuates between about 14.5 and 14.9 once every couple of seconds, but can be right on 14.7 for breif periods of time.
xviper, The FJO indicates an average of 14.7 during normal idle. This usually fluctuates between about 14.5 and 14.9 once every couple of seconds, but can be right on 14.7 for breif periods of time.
