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Old 03-31-2010, 10:57 AM   #4 (permalink)
Daox
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Very simply, open loop is when you are not running at stoichiometric air/fuel ratios. Your vehicle is using the maf or map sensor in combination with a few other sensors to determine how much fuel to inject. In this mode you are almost always injecting more fuel than necessary (except in a fuel cutoff situation, in gear deceleration for instance). During closed loop the fuel injection is based mainly off of the oxygen sensor in the exhaust. It holds the air/fuel ratio to stoichiometric ratios and is in general more efficient than running in open loop.
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