Hello,

This is my first post to this board, although I have leaned lots
about working on my 1990 240 from this board in the last few year.

I recently failed California smog for a leak in the fuel evap recovery system.
Using clever methods from this board, I have trace the leak to a poor
sealing surface on the fuel filler neck where the gas cap gasket is supposed
to seal. The filler neck may not be round or it may be scratched or something
that prevents a good seal at that location.

Replacing the gas cap is not the answer - the smog test includes a off the car
test of the gas cap and my gas gap passes. The test that my car failed is when the smog tester pinches off the hose to the charcoal cannister, then puts a cap on the fuel filler, and pressurizes the system with nitrogen to 0.5 PSI. The pressure must not drop below 0.45 PSI in a few minutes. Mine drops right away.

My system holds pressure if my fuel filler neck is sealed with a bicylce inner tube stretched around the neck and thereby sealed.

Any ideas on how to fix the fuel filler neck so it gets a good seal, in place ?
I would rather not remove it and mess with the gas tank connection.

thanks for any ideas.