Scotty C
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Registered: 6th Nov 05
Location: Kidderminster Drives: 1.6 16v Sport
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I swear I heard Clarkson once say ''That a modern diesel engine uses NO fuel whilst coasting in gear (engine braking) so when you pull upto a juction you're getting those 300 yards or so for free'' This was on the one where he took that big Audi to Scotland and back with one tank of fuel.
I didn't think much of it, until we was on braking systems at college, and my teacher mentioned that a big lorry has to use engine braking when then the air brakes get too hot - basically as soon as your foot is off the pedel in gear, the injectors shut down so no fuel is being used to help to stop the vehicle.
So, that's the case with lorry engines, what about cars?
Thanks 
[Edited on 09-11-2008 by Scatt]
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Ian
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Registered: 28th Aug 99
Location: Liverpool
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It's the case with most modern engines. Vauxhall call it deceleration fuel cut off and if I remember correctly it's been a feature of everything they've made for years.
The difference between lorries and cars is that the lorry will have more momentum so the engine will continue to turn with no fuel with just the weight for propulsion. In a car, there is still a certain amount of fuel required in most cases to keep it from stalling, ie. enough fuel for tickover which presents itself as deceleration when you take your foot off. You see mileage in the hundreds on the trip computer. You need a bigger hill to see it jump to 999, which it will if fuel is cut completely.
There's also a lubrication issue with diesel engines, not sure how that is got around. Perhaps it doesn't matter for short spells.
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Scotty C
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Registered: 6th Nov 05
Location: Kidderminster Drives: 1.6 16v Sport
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Oh right. Didn't know petrol engines did it too.
My brothers Astra is always reading 999.9MPG when going down hill, good to know it's using to no fuel 
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Fro
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Registered: 20th Jun 06
Location: Rainham, Essex Drives: A3 2.0TDi Sport
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Pretty sure 1.6 sports did this as im pretty sure i read it in the manual.
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D-A-V-E-
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Registered: 2nd Mar 08
Location: Northern Ireland!
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My dads 2.2 petrol omega reads 999.9mpg when you lift your foot off the throttle....is this the same thing??
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Scotty C
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Registered: 6th Nov 05
Location: Kidderminster Drives: 1.6 16v Sport
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quote:
Originally posted by littleredrocket
My dads 2.2 petrol omega reads 999.9mpg when you lift your foot off the throttle....is this the same thing??
Yup.
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