Quote:
Originally Posted by UFO
... when the CEL is lit, the ECM will retard the timing to avoid the creation of NOx and mileage will decrease.
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Bingo! there's your reason for FE getting worse by removing EGR.
EGR wil improve FE
at the same NOx level, however,
if all the other engine settings are the same, I have never, ever seen FE improve with EGR on a diesel.
This is the whole reason for the EGR vs SCR debate on diesels (see article here:
http://fleetowner.com/management/feature/scr_egr_0701/). An engine with EGR has lower NOx emissions, but worse FE. SCR can clean up the NOx after it's left the engine, but not having to use EGR buys you FE. Of course SCR means you have to add DEF (diesel exhaust fluid).
If EGR improved diesel FE, SCR would have both DEF and worse FE, so there would be no point.