Tim Comeau

Anybody have a quick answer as to why Porsche stopped using the vacuum check valve on the 88 models?
There's a roll over check ball and a vacuum valve on the earlier cars right where the filler neck mates up to the gas tank. Did they add something else or replace the check valve with something else. The PET cd doesn't help much. It shows a different hose without the valve for the 88- cars.
I didn't see anything on Clark's Garage about this.
Reason for asking:
I have an 88 924S that passes smog, but won't pass the new Calif. fuel evap test where they pressurize the fuel tank system and check for leakdown, thus for fuel vapor emmisions.
I'm aware that the big, heavy Calif. gas pump handles cause the top of the filler neck to oblong after years of use. I've rounded off mine again and it doesn't seem to be leaking air there.

Mike C.

Good question. I discovered the same while trying to diagnose a fuel smell problem in the (early 85) car. I pored over the diagrams but couldn't figure out what had changed so that the vacuum check valve was no longer required.

Tim Comeau

All the pre-88 944's have the check valve according to the PET CD.
I've heard of a cracked fuel tank....
I have 2 early steel tanks to swap in if that's the case. That would be a majorial pain in the bumpus.

Mongo

They may have deemed this vac valve irrelevant to the setup on the 944. Maybe something that could have been over-engineered on our cars.