I'm helping a friend fix his 05 ML350. Besides a few things I fixed already, it won't take fuel.

I took it to the gas station, takes a dollar than klicks. The fuel is violently gurgling enough to splash out of the filler neck.

I think the system works by (using a pressure sensor on the filler neck) to open the canister vent valve to allow fumes/air to vent out.

Any ideas or pointers on this issue? Thanks