Quote:
Originally Posted by razor02097
I don't think so. If it were emissions then DFCO wouldn't have been used. There is no way to accurately measure the efficiency of the engine when pumping pure air through the exhaust in an engine running state. That is why variable displacement engines physically hold the exhaust cycle so when the cylinder is active again it can expel the exhaust and intake air and fuel.
Think about it the O2 sensor senses O2. You pump ambient air past it and it will swing crazy lean. The ECU responds by adding fuel to that bank.
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It is the same problem in both regards with respect to lean-burn. EDIT...
EDIT: the fuel mixture issue is solved with a wideband O2 sensor.
EDIT EDIT: sorry, I'm not so certain about emissions. Lean-burn doesn't work with a 3-way cat because of the exhaust chemical composition - my bad. Low cat temp during DCD seems like a reasonable presumption to me. Maybe this is an effect I could quantify on paper if I thought about it. My understanding is that DFCO is intended to protect the cat from unburnt fuel under deceleration. The fact that it is done, and done at a low air mass flow rate I might add, may not be an indicator that DFCO is good for emissions. Perhaps it's a compromise in that regard. Tolerate cat cool-down instead of destroying it permanently. EDIT EDIT EDIT: I can find opinions, but haven't found anything definitive on the design intent of DFCO. Can you?