I started to smell gas fumes from y Aerostar, both while parked and driving. At first I thought it might have been the gasket on the fuel sender plate, which I've re-seated before. But after replacing that, the odor persisted. On a hunch I looked at my evap canister (had to remove the air filter box to get to it), and found that elbow had somehow come off of the nipple on the canister. The elbow was also kind of deteriorated, as Aerocolorado described. It seemed the line leading up to it was a little tight, and maybe that's why it pulled off. But I noted that the elbow on my Mustang, 3 years older, was still in good shape. After verifying that the nipples were the same size, I got another elbow from my local salvage yard, from the same vintage Mustang, and replaced the rotted one on the Aerostar. The gas smell has stopped, so I think I fixed that problem.

Here are some simple things to check:

If you pull the tank vent line from the canister and pull off the gas cap, you should be able to blow through that line with no obstruction. If you replace the gas cap, you should not be able to blow through that line.

If you pull the engine line from the canister (engine off), you should not be able to blow through it, as the purge valve should shut off the line.

If you then re-install the engine side line, and install another line to the tank side nipple and try to blow into it, it should also be blocked. The vent cap on top of the canister should be one-way, only allowing air to go in when the engine is purging the canister (opens with negative pressure).

I would not recommend sucking on any of these lines, as they can all have fuel vapors in them.