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Old 09-03-2010, 11:48 AM   #7 (permalink)
dcb
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pimp mobile - '81 suzuki gs 250 t
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OBD mpg gauges usually makes an assumption that the air fuel is close to 14.7 to 1, which is reasonably accurate for a modern fuel injected/o2 sensor feedback gasoline car.

On diesels the air is not throttled, thus the air fuel ratio is all over the place, usually very lean, so you cannot expect consistent results.

I would expect that subtracting .2 l/100km from the OBC in your head would be the way to go for accuracy. the on board computer should have a very good idea how much fuel it is injecting, or at least be off by a consistent amount.
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Last edited by dcb; 09-03-2010 at 11:59 AM..
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