I like the idea of the smoke test. In my E39 it has been an exceedingly cheap way to diagnose any and all leaks. Now whether I want to know about those leaks is a different question. But a $50 kit pays for itself in its first use.
On USA models, the vent does not go thru the trunk floor, it goes to the expansion tank and has a blue hose that runs thru the car to the charcoal canister under the batteryCheck this venting from the filler neck, the hose shall have an outlet to the underside of the car (rear part of the tank) The hose may have popped of the rubber sleeve.
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This is a typical crack in the white plastic sleeve. It gets hardened and than cracks. Must be thoroughly checkedYes the plastic sleeve is in place. I guess the fuel hoses are next to be changed.
