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Old 08-05-2011, 01:30 PM   #14 (permalink)
hackish
Calibration Engineer
 
Join Date: Jan 2010
Location: Canada
Posts: 86

Subie - '00 Subaru Impreza STi JDM
90 day: 22.49 mpg (US)
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Quote:
Originally Posted by t vago View Post
Besides that, hard acceleration is bad in some OBDII vehicles because those vehicles' engine computers will go into open loop and perform enrichment of the fuel/air mix to the point where you'll see AFRs of 12:1 or even 11.5:1 (like my truck, for instance). Fuel economy goes right out the window, even if you wouldn't have to brake hard.
This is true, although many newer vehicles are staying in closed loop much longer. Some of them will stay closed loop for everything but WOT.

I just did some testing on a 1.9l TDI and actually found that the engine was more efficient under higher load with more fuel than factory. Surprised me but I don't tend to tune a lot of Diesels. Sadly, adding fuel sure didn't help the emissions. The HC and particulate readings were sky high
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