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Old 07-17-2017, 10:08 PM   #41 (permalink)
JSH
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Join Date: May 2009
Location: PDX
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Adventure Seeker - '04 Chevy Astro - Campervan
90 day: 17.3 mpg (US)

Dieselgate - '14 VW Jetta Sportwagen TDI
90 day: 38.24 mpg (US)
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Quote:
Originally Posted by Old Tele man View Post
Automotive MPG gauges are only high-tech "guesstimations" based on the premise that the A/F-ratio is always 14.7:1 which is NOT absolutely true (initial start-up, wot, over-heating, etc.)
When I connect a cheap OBDII scanner to my car it shows A/F ratios that vary based on conditions. Are you saying the onboard computer throws away this information and replaced it with a fixed number? Why would it be programed to do that?

I've found the onboard fuel economy gauge to be quite accurate in my cars. In the 130K miles I had my 2005 Prius the difference between my calculated MPG and trip meter was 1.4%. Tank to tank it could be huge (up or down) but the average was very close. I trust the MPG gauge more than the gas pump shut-off.

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