Getting a P0442 (small leak) & P0455 (large leak). This only happens when I get down to about a 1/2 tank or less of fuel. Stopped back at the dealership as they had just replaced the fuel tank a couple of months ago. They stated that they had checked all of the evap system back by the tank according to the service write up guy and everything back there was okay after replacing the gas tank which they said was rusted. According to the write up guy, the evap system only functions when the take is less than 3/4s full. The system was smoke tested earlier this year by the previous owner and he stated they couldn't find anything. I'm thinking it must be in a line betwen the canister in the rear and where it feeds into the manifold, but I can't find any good schematics. My tank is full once again and my MIL remains off. Anyone have any ideas as to where the problem most likely resides? I don't just want to start throwing parts on until it goes away, I would like to do a systematic test and find out what is wrong! I might add that this is a vehicle that resides in Mid-Michigan. Also vehicle has 182000 miles on a 4.0l I-6.

Thanks,
Bill

 

The rep is right in that it only takes readings around 3/4 full. Evap leaks are hard to find sometimes and really the only way is with a smoke machine. If the leak was there with the previous owner then I think the dealership is probably not the cause with the gas tank replacement. Perhaps try a good reputable independent shop. Without a smoke machine you are just taking guesses and throwing parts at it unless you see an obvious leak spot like a rubber line or a hose off or a cracked rubber on the gas cap.