Quote:
Originally Posted by Freon
So, the ECU certainly DOES have an idea as it uses the oxygen sensors to trim fuel. It should complain (i.e. throw a CEL) if your gasoline content is off too much and it has to trim more than is "acceptable". Pretty much any car with oxygen sensors will try to trim fuel to some extent, and here in the states even pump 87 can have 0% to 10% ethanol content. Newer cars are extremely savvy with it and store all sorts of various fuel trims for different situations.
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The ecu will adjust to the new AFR, but it can't and won't adjust far enough because of the great difference in target AFR. It can only adjust so much and will run you lean. That's the whole point. Yes O2 sensors read the amount of fuel in the exhaust and use that for targets, i never said they didn't. But its much easier to describe in terms of calculated AFR.