2000 5.0L explorer evap problem

[Paveway]

I have a 2000 XLT explorer with the 5.0L V8 in it.
Over the last few months, my fuel economy has dropped through the floor. I used to be able to do about 400-440 km a tank (roughly 14 mpg combined city/highway) though now it's dropped to about 280 a tank (roughly 9 mpg) I've done a recent tuneup on it, replaced plugs, air filter, and fuel filter. When I do a scan with my diagnostic scanner, it doesn't come up with any codes, but it flashes the yellow light and the evap icon. Any ideas from anyone on where I should go from here?

I have also noticed a bit of a power loss, more noticable at highway speeds

 

[robertoa1a]

It's posible you have two spark plug wires crossed.

I have a 5.0 and it gets great fuel economy like 21 mpg. I can't convert that to metric in my head but, I would start looking at everything under the hood tune-up wise. The diagnostic system doesn't always pick up problems. The exaust should not smell like fuel and should not smoke mutch at all. Its hard for some people to tell in the winter because fog comes out. If your exaust smells like fuel then it isn't being burned in one or more cylenders. Instead the computer tries to compensate by adding more fuel. You need a volt/ohm meter to check your coils. A repair manual from your parts store is cheeper than the gas you are using and has all the specs. If you cant find one just reply and I,ll look stuff up for you. Old spark plugs tell a story about what has been going on in your engine by wear, deposits, and color.