Ray, I'm not one of the seriously brainy boys you're looking for, but I've had similar duty cycle test results, with a 90% engine running measurement. Super lean, right? Yet the fuel consumption/mileage has declined to the mid-teens city/21 hwy. At some point, I'd think we should be taking the next step and testing the O2 sensor and EHA. Maybe the seriously brainy crowd can weigh in on that, too.

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1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
MBCA member

Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

There are only 10 kinds of people in the world--those who understand binary and those who don't