97 Ford Expedition CE light Large Evap leak

I have a 97 Ford Expedition with a check engine light on. Took it and had it diagnosed, the diagnosis was a large evap leak. They suggested replacing gas tank lid. We replaced that, and it is still coming on. We had it looked at by 3 different mechanics, and they all came up with the same answer. Has anyone had this same problem, if so how did you fix it. If no one has had this problem do you have any suggestions on what else it might be. :banghead:

Please post exact code number and engine size.

I have a 97 Ford Expedition with a check engine light on. Took it and had it diagnosed, the diagnosis was a large evap leak. They suggested replacing gas tank lid. We replaced that, and it is still coming on. We had it looked at by 3 different mechanics, and they all came up with the same answer. Has anyone had this same problem, if so how did you fix it. If no one has had this problem do you have any suggestions on what else it might be. :banghead:
was it diagnosed at a ford dealer?

Thanks for the replies. The exact code that we are getting is a #455, and the engine size I am assuming you are asking is 5.4 liter V8. We have a mechanic that we use, and try to avoid the Ford Dealership here because they just take so long. If we can't figure this one out, that is our next stop.

Anymore ideas on this one? Thanks for the ones received.

You will probably need a "smoke machine" hooked to it to find the leak. There are hoses that run from the fuel tank to the front of vehicle with valves in them. There is also a fuel tank vent that may be hanging open not allowing the pressure to build up for the test.

Is this something I can get a hold of, or is it a dealer thing? By the way thanks for the info from you.

You will probably need to take it to a shop. These machines are fairly expensive for a DIYer. Other options are get a lot of friends to smoke big cigars and blow in tank:grinno: :grinno: :nono:

I like the last idea better, might be kind of funny getting light headed and all. Thanks

I have owned my 1997 Expedition for about 6 years. I too have had this problem with the check engine light on. It does nothing to my fuel mileage or the performance of the car. I simply covered it with a piece of black electrical tape. Out of sight - out of mind..

Has the gas cap been checked? Most of the time a gross leak is due to a loose gas cap or a seal that has been damaged.

You can start visually inspecting all the vent lines to the tank. Use wire ties as hose clamps on the hoses going to all the tank vents and the charcoal canister. I use to work at an E.P.A. shop and almost every car failed because the vent hoses were not clamped. These were new high end cars.
The machine used to detect vapor leaks is the same or similar to the one used for emmission testing. Look at your gas cap to see if the seal is compressed or damaged.