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Old 01-30-2012, 07:59 PM   #15 (permalink)
MetroMPG
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Join Date: Nov 2007
Location: 1000 Islands, Ontario, Canada
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Blackfly - '98 Geo Metro
Team Metro
Last 3: 70.09 mpg (US)

MPGiata - '90 Mazda Miata
90 day: 53.56 mpg (US)

Winter beater Metro - '00 Chevrolet Metro
90 day: 61.98 mpg (US)

Fancy Metro - '14 Mitsubishi Mirage top spec
90 day: 58.72 mpg (US)

Even Fancier Metro - '14 Mitsubishi Mirage top spec
90 day: 64.03 mpg (US)
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When an engine with computer emissions control is first started up, it's in "open loop" mode, where the engine runs on quite a pre-set, rich air-fuel mixture. Once it begins to warm up (including the oxygen sensor(s)), it goes into "closed loop" mode where the air/fuel mixture is set by input from that sensor, and goes from running rich to stoichiometric (14.7 to 1).

Oxygen sensor - Wikipedia, the free encyclopedia

The faster your engine goes into "closed loop" after start-up, the better for emissions & fuel economy.
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