The fuel tank on my 1997 740i has been building up great amounts of pressure. It is almost impossible to get the gas cap off and then when it does come off there is a huge "whoosh" sound from pressure release. My mechanic said to get a new ventilated fuel cap but problem remained. My fuel tank on the drivers side has actually imploded and is sitting in my garage leaking gas. This problem is also causing the fuel to stop flowing when I get down to 1/4 tank. BMW says there is no recall on this issue. Seems like a dangerous situation to me.
Yeah pretty common thing it seems. It's generally related to the charcoal canister, which was actually redesigned on 3/97 and later models to try and avoid this particular issue. What specific month model is your car? It's possible yours was built just prior to this change coming into effect (remember there's a difference between the PRODUCTION date and build date - my car is a 1996 build but production was in 95 for my motor, if I've got that right).
My 09/00 740iL is doing this too. Used to be a loud thumping after being left overnight followed by a funky whistle sound. All goes away if fuel cap is left off.
Given the production year, I have the newer vent hose and just replaced the vent piece by the fuel pump.
Thump has become less intense and loud but whistle is still there.
Does anyone have pics on how to vent fuel cap by drilling holes?
Just turn the (spare) cap over and drill a 3mm or 1/8" hole in the centre of the metal part only. This will solve the bong problem for the moment. I lived with this for a while, as I couldn't trace the source, so in the end I did change the charcoal canister, put my original cap back on, and no bong since.
I'll drill the hole and eventually replace the charcoal canister as that is likely the issue even though I'm not pulling codes.
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