I've had my 98 outback on the road about 700 miles now since the engine swap using a 95 legacy 2.2 motor. The p0440 code has come up 3 times now resetting it each time it just comes back a few hundred miles later each time. What do I need to look at? When I open my gas cap the woosh sound is not present like it was on the 95.

Not sure why 3 posts occoured. Please delete the other 2 my phone posted too much

possible hole in the filler neck - often, older soobs have serious rust on the other side of that the plastic cover.

I have same problem with my 98 ObW. I replaced the filler neck, but still must have a vacuum leak somewhere in the gas tank system. It could also be a bad gas cap that is not holding a vacuum. Tracing down that code and fixing it is pretty much trial and error. As mentioned earlier, it could very well be a leak in the filler neck. Salt and crud builds up between the filer neck and the plastic shroud that covers it. I replaced my filler neck, and threw away the shroud, as I did not think it worth the trouble to replace it.