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Old 10-05-2014, 08:39 PM   #7 (permalink)
ever_green
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Join Date: May 2011
Location: Toronto
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gueff - '19 Mercedes Benz A250 4MATIC AMG
90 day: 30.55 mpg (US)
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yes that's correct. I'm monitoring my EGT using scangauge and romraider datalogger...EGT jump significantly under stoich or leaner conditions with just a slight increase in load.

for example cruising at 40 mph @1800RPM the egt is around 500-530'c . move up to 60 mph @2500 RPM where load increases from 35% to 45% and EGT jumps to +650'c. that's quite a bit of increase for just a slight increase in throttle opening and RPM, and this is at stoich operation! don't get me started on lean tempratures at mild RPMs, i have managed to max out my sensor's voltage by just flooring it at 2500 RPM with lean fueling. Therefore i'm running richer under load and leaner under cruising condition for balance of fuel economy and reliability. sure the EGT are higher but not high enough to cause damage, which is why i'm not going leaner than 16:1, plus going any leaner can cause surging. Also it's quite difficult to stay in lean conditions as it requires low engine loads, which pretty much restricts me to ~45 mph cruising speeds. However in combination with pumping friendly drivebywire and over square engine operation it nets me good results ~38 MPG which is not bad for a full-time AWD 3200 lbs sedan.
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