On my 2000 SLE.....its got 78K on the clock.

I only got 350 miles to my last tank in the car... i drive 40 miles each way to work.....90% of that drive is 60-65 highway speed. I don't drive the car hard at all....

I have put a brand new gas cap on it from stealership.

Here are a few probably stupid questions....
1. When you remove the gas cap and put the gas pump filler in, you see a metal flap of sorts that is spring loaded at the filler neck. i noticed mine does not fully close for whatever reason..staying open some. is this a problem?

2. When i stopped at a light over the weekend, i noticed a gas smell and happened to look out my side view mirror....and i saw what looked like gas fumes coming from the gas cover area........

All i know is that the new cap is definetely on all the way...always make sure i click it many times when putting back on. Also, i have cleaned the metal on the filler neck to make sure of good seal.

I picked up new TR55 plugs for the car, but, hadn't bought the wires yet. Was going to start there on the tune up.

Any ideas on the gas smell/cap issue? Always the same P0440 code.

There are many things that can cause the P0440 code. Once common issue is the vent valve near the rear tire. Taking it apart, cleaning and lubing, and reinstalling often solves the problem. Other areas to check are the filler neck, the evap cannister under the car, the solenoid under the hood, as well as all of the tubes, and connections for each.

thoughts on the metal flap on the filler neck not closing all the way? this be a problem?

I believe the gas cap will seal that area pretty well, so I don't think it is a problem. I can't give you a 100% on that, though.

Follow Archon'* advice and check those items he mentioned. One of them is likely to be the culprit.

If you check each one of those items and the problem persists, then you should also do a careful and thorough check of all your vacuum lines, hoses and connections. Small cracks in your rubber connectors or lines can and will produce the P0440 code too.

It is most likely that the fix for this will be very inexpensive, just tiresome to trace down.

question....can the vent solenoid issues cause bad MPG on the car?

I ordered my beldon wires today. got my Tr55s also...will put that all on this weekend...as well as basic tune up items. Starting to wonder if its time for a new O2 as well.

i can't say that it is a sudden issue really. have only owned car maybe 2 months now..and hadn't checked or watched mileage till now.

i am working with the solenoid or vent back by the rear tire tonight...

only thing i am seeing is the rubber lines that tee and whatnot on the assembly were dry rotted looking and crumbling. so i replaced those...not sure what else i can actually do on that assembly though.

If the lines were crumbling, that could very well be the problem that is setting the code. The vent valve comes apart by un-clipping the plastic tabs that hold it together. Clean it up, lube it with either silicone, or white lithium grease, and reassemble. A problem in your evap system will not be the cause of poor gas mileage.

Whenever I see that, my first thought is that someone tried to siphon gas.