fuel leak

I have a 98 Suburban 1500 4 x4 . . .. a while back it began leaking fuel out the gas cap area. It would do this every other tank or so . . . sometimes every three tanks. It would continue doing it even when the tank was just over 1/2 full. We would clean teh gas off the paint only to find that it would happen again the next time we drove it.
We had the local dealer look at it. They checked teh cap, deciding that was not it. So the ran a nitrogen pressure test but found no leak in the tank or neck. So we tool it to our local mechanic. They dropped the tank and found a tiny leak at soem o-ring at the top and fixed that. But the problem returned teh next day or so. So we took it in and they completely replaced the fuel tank. We got it back and teh very next day the thing wouldn't run at all. This may be unrelated, I'm not sure. What they found was the master fuel injecter (not sure the name - sends fuel to the 8 injectors) was shot. Later we also found that the fuel filter was toatally plugged so we replaced that.

So . . . what would make fumes and gas come out at the gas cap area? The smell is very noticable and not just when the tank is full. It's in tehshop now, and the mechanics are stumped.

Can anyone help me and send advice? Could there be a relation between the two problems? Up until we took it in it ran fine but leaked fuel. Is there something up front in the engine that could be causing enough pressure to send fuel back out at the cap? Has anyone heard of a similar problem?

I'm grateful foro any advice you can send my way.

Could be a clogged vent, or a problem with the purge canister. If the canister is not being vented to the engine, or the vent line is clogged, these kinds of problems can occur.

Thanks for your reply. Are the vents in the tank itself? The shop is looking at the fuel cannister now. I hope that's it.

The vent is a sealed line (hose) that runs from the tankl to the canister. This keeps it from emiting gas fumes out to the atmosphere. I hope they find your problem.

The canister is up front by the radiator on my 97 and is about the size of a coffee can with rubber hoses going in the top, right under the top radiator hose and next to the "storage box".

You should replace the fuel filter every 20k miles no matter what this problem is.

The fuel injection system pumps more gas than the injectors can use so there is a pressure regulator on the fuel rail that allows fuel to go back to the tank thruogh the fuel return line. There shuold always be fuel returning to the tank unless you are at red line and full throttle, even then there shuold still be fuel returning to the tank. The pump is designed to over supply the injectors so they never are starved for fuel. That's why there is the fuel return line on all fuel injected engines.

The vent lines may be pinched or clogged. They are at each corner on the top of the tank and then connected together near the middle of the tank. They should run air through them and make sure there are no cloggs or pinches all the way up to the charcoal canaster. Then make sure your canister is not clogged. Also have them run air from the front back to the tank to make sure the black plastic connectors on top of the fuel tank are not clogged (leave the gas cap off for that test to see how much air comes out).

I had old BMW with a clogged canaster and the tank would actualy pop when it expanded from the fuel pressure, yours is probably leaking instead. When I got gas the cap would fly about six feet if I didn't hold on to it tight.