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Old 02-06-2012, 06:23 PM   #1 (permalink)
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Engine off coasting?

How long do you need to coast before you actually gain increased mpg? Engine off for more than 6 seconds? At what point does it actually cost more to start (fuel enrichment) the engine back up vs just engine on coasting?

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Old 02-06-2012, 06:31 PM   #2 (permalink)
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It depends on how long and how hard you used the gas pedal before you started the coast, and how long your trip is. Typically with a Scangauge or Ultra-gauge, you'll see immediate mpg gains when you start coasting, within a block or two. Get instrumentation like that, and eliminate the guesswork.
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Old 02-11-2012, 01:24 AM   #3 (permalink)
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If you bump start does it change the mixture? (Specifically Mazda F2 engine)
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Old 02-11-2012, 03:18 PM   #4 (permalink)
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I have heard that the engine if left off to long (eoc) then when fired back up the ECM goes into fuel enrichment ... I am not sure..just curious..
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Old 02-11-2012, 07:04 PM   #5 (permalink)
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Quote:
Originally Posted by Georgboy View Post
I have heard that the engine if left off to long (eoc) then when fired back up the ECM goes into fuel enrichment ... I am not sure..just curious..
Again, it depends on the ECU software. My 2002 Sentra went into open loop (enrichment) for a full 4 minutes following any EOC. My 2006 Scion stays in closed loop most of the time when restarted, even after a 5 mile EOC.
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Have you ever noticed that anybody driving slower than you is an idiot, and anyone going faster than you is a maniac? George Carlin
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Old 02-11-2012, 07:27 PM   #6 (permalink)
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5 miles is a long coast, those are definelty worth turning the engine off, but for anything under 30 seconds i don't think it's worth turning the engine off
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Old 02-11-2012, 10:35 PM   #7 (permalink)
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Similar question: What's the shortest time where turning off and re-starting your engine is a net gain over idling? Or, at what time is it the same or better to idle, if any?
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Old 02-11-2012, 10:49 PM   #8 (permalink)
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The automotive pundits say 7 seconds is the magic number with modern fuel-injected cars. Shut your engine down at any stoplight where you'll be idling >7 seconds. You'll use less gas to restart it than you'd waste idling. The EPA says $.17 of every gas dollar is wasted idling.
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Boycotting Exxon since 1989, BP since 2010
Have you ever noticed that anybody driving slower than you is an idiot, and anyone going faster than you is a maniac? George Carlin
Mean Green Toaster Machine
49.5 mpg avg over 53,000 miles. 176% of '08 EPA
Best flat drive 94.5 mpg for 10.1 mi
Longest tank 1033 km (642 mi) on 10.56 gal = 60.8 mpg
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Old 02-11-2012, 10:52 PM   #9 (permalink)
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Thank you. Now does that figure change with kick-starting?
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Old 02-11-2012, 11:06 PM   #10 (permalink)
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Quote:
Originally Posted by wanderling View Post
Thank you. Now does that figure change with kick-starting?
Probably not. The 7 second comparison is strictly fuel used. It doesn't consider electricity to crank the starter. Bump starting is more efficient than using the starter, but you may pay by replacing your clutch sooner.

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Darrell

Boycotting Exxon since 1989, BP since 2010
Have you ever noticed that anybody driving slower than you is an idiot, and anyone going faster than you is a maniac? George Carlin
Mean Green Toaster Machine
49.5 mpg avg over 53,000 miles. 176% of '08 EPA
Best flat drive 94.5 mpg for 10.1 mi
Longest tank 1033 km (642 mi) on 10.56 gal = 60.8 mpg
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