What the heck causes the loss in fuel economy?? I was averaging 17 mpg up until a couple of weeks ago and bam, down to 12. My driving for that mileage was 75% city and the rest highway. Is the fuel being mixed with K1 do it ? If it is then is there less btu's in kero than diesel. Also the exhaust smells alittle different now, not quite as propanie as before.