We recently had on 2 occasions where after filling up, the mileage on 
our 2002 Cougar went down to 26 MPG, and remained there several 
tankfuls, and the after taking on fuel at a  certain brand station in 
Ohio, mileage went back to normal. This is on a 700 mile trip that we do 
frequently with usual fuel stops. The vehicle's on board instantaneous 
and average mileage computer readings were confirmed when our first fuel 
stop was 60 miles short of our usual stop. I blame it on poor quality 
fuel which likely was gasohol.

Briggs & Stratton Engine have a $8 alcohol percentage checker, it is 
basically a calibrated cup that one adds water.

Bob Blick wrote:
> microsoftwarecontrol wrote:
>   
>> I checked my car. It is running at too rich codition and using 20% more gas.
>>
>> !t not make engine light on, only reduce mileage per filling tank.
>>
>> I read, o2 sensor can decade! 
>>     
>
> What test did you perform to determine it is running too rich?
>
> Because if an O2 sensor is bad enough to change the mixture, it is
> likely bad enough to trigger the check engine light an any fuel injected
> car.
>
> Mileage is a poor indicator of mixture. Anything can affect the mileage.
> Snow. Alcohol in the fuel. The nut behind the wheel.
>
> Cheerful regards,
>
> Bob
>   
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