> How much fuel does an engine use when you are going downhill with your
foot
> off the throttle, using engine braking? I'd expect it to be about as
much as
> with the engine idling. Just because the engine is running faster and
> there's a greater throughput of air due to the more frequent induction
> strokes, why should that cause more fuel to be used, assuming you have
fuel
> injection rather than a carburettor?
It causes more fuel to be used because the engine compression retards
your increase in speed, decreasing your roll out and requiring you to
come onto the gas sooner.
If you let gravity accelerate you in neutral you WILL find that many
hills will do work for you that require significant throttle just to
overcome the engine compression at the RPMs that your engine spins at
at this speed.
Shit...just coast on a flat. See how far you roll, losing little
speed. Then, try the same thing by lifting your foot off the
accelerator.
> Is the fuel consumption the same if you coast downhill with the engine
on
> but the clutch pressed and/or the transmission in neutral?
the fuel consumption is the same WHILE you are going downhill,
HOWEVER, in SOME cases, overcoming engine compression requires
ADDITIONAL fuel.
Trav
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