Getting back to the question at hand...how can a car which otherwise runs normally be only getting about half the mileage it should be getting? We confirmed it was running normally by having Terry drive and examine it. He owns the same model and confirmed there is nothing unusual about this one. Typically, things that come to mind which would affect MPGs could be:

1) dragging brakes (let's assume you don't drive with one foot on the brake pedal - so called "riding the brakes")
2) slipping tranny
3) clogged exhaust
4) bad injector(s)
5) injector timing
6) fuel leaks
7) ECU/Sensor problem

Since Terry says the car drove more or less "normally" I would tend to eliminate 1, 2, 3 and 4. That leaves 5, 6 and 7. I'm assuming Terry also would have noticed fuel leaks, even if they were not from the usual locations, though you could have one that only occurs under certain conditions. I guess if it was my car I would have the injector pump timing checked to make to someone didn't mess with it. It is not that costly to have it done, even at the dealership...I would guess a couple hours labor if they claimed they had to remove the Intake Manifold to do it.

I'd also invest in a scangauge II and try and monitor MPGs from it to see what it reads. That will confirm if you really are completely free of any leaks. Maybe you have a leak which only occurs while you are driving?

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz