Evaporative emission system faults 996, 997

I get the P0455 major leak combined with P0450 Tank pressure. Watching my driving habits, I reset the code - and it comes on reliably after about 30 minutes of driving while taking off from a stop. Seems to be coordinated with letting the clutch out - could it be because the pressure is dropping to the vent valve with the RPMs? Is there a recommended way to check the function of the vent valve before I replace it? Thank you for your expertise.

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[Casey at Pelican Parts]

What year is your Carrera? Seems to me that you've got an evap leak somewhere. The source of the leak could be the evap canister purge valve. I would recommend using your scanner to check the fuel trim values while out on your drive. If you notice them moving all over the map rich and lean chances are you have a faulty evap canister purge valve. If they stay mostly lean I would be looking for an EVAP leak. The purge valve is located in the engine compartment on the driver side.

- Casey

[Frogger80]

Thanks, it's an '01. Thought I had this fixed with driving habits, until it came on again about a week ago (while best behavior in place). I'm using the Durametric scanner, and don't see a reading for fuel trim -- or anything particularly relevant in this area.

Thanks for the suggestion on the canister purge valve... I was originally thinking it may be the fuel line vent valve... which I need to research more... they seem the same, but different location across different years? I suppose it could be a general evap leak, but that sounds difficult/expensive to diagnose...

Thanks for any more advice.

[Frogger80]

Thank you for the advice.
Mine is an '01. Is this the same as the Fuel Line Vent valve?

I'm using the Durametric scanner, and don't have a reading on Fuel Trim... or any thing else that seems relevant. I guess your recommendation may have been for a different year.

I'll start digging in and looking for a general evap leak, but that sounds a bit more time consuming.