The E30 was built with with a vent-free fuel cap, and it was for a reason. If you’ve ever placed your finger on the end of a straw with liquid in it, you will have found that the liquid doesn’t fall out the bottom.

Similarly, the 80’s fuel system is designed with this pressure difference in mind. If the gasket at the fuel cap is leaky, it will not allow for pressure to form and therefore allow vapors to escape freely. You would think that the smell would come out the back, but it most often comes out of the engine bay, from the charcoal canister vent.

Ferrari actually explained the how a fuel system from the 1980’s works pretty well in this period correct manual:

If you’re running an original E30 fuel cap, there is a 99% chance that after this amount of time, it is no longer sealing.

Luckily the seal is under $20 from the dealer, or ~$50 for a whole new cap.

This entry was posted on August 16, 2021 at 9:27 pm and is filed under Do it Yourself. You can follow any responses to this entry through the RSS 2.0 feed.