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Old 02-20-2015, 09:18 PM   #6 (permalink)
darcane
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Quote:
Originally Posted by California98Civic View Post
Maybe it is more accurate to say "fuel trim"? The UG displays a fuel trim figure based on readings from the O2 sensor. It displays as, for example, -10.9, and the manual says to read that as a percentage change from 14.7:1
Ah, OK, that makes more sense.

Fuel trim doesn't directly tell you what the AFR is doing, it tells you how long the fuel injectors are being held open relative to how long they should be held open for the current conditions (load, air flow, intake temp, etc).

So, a negative fuel trim means that the O2 sensor is reading rich, so the computer is cutting fuel to compensate for it.
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