Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Faint hissing coming from fuel cap

Thanks for this John. Still lots to learn with using this forum 😂

I dare say if you bypass that valve and just connect the pipes, that would prove if the valve is defective or not, it’s only air in the pipe (unless the car is upsides down).

Think I've now planned my weekend now. I don't get any warning light from the ecu so I'm going to blow through a few pipes to make sure there are no blockages. I'm beginning to understand how the EVAP system works from googling, but because fuel evaporates I can't find any reason why the whooshing sound when opening the filler cap, can't be the fuel tank venting into the filler hose. I assume there is no one way valve from the filler, into the tank.

The standard cars don't have a rollover valve like that Craig. That's a modification by the dealer....

Shouldn't the open end of the rollover valve be connected back to the EVAP charcoal canister??

Otherwise it's venting to atmosphere.

Update regarding the hiss. I've ordered a refurb kit for the filler cap from ceandess and waiting for it to arrive. I have since solved the issue of the hiss. I dismantled the locking mechanism from the cap, as when I pressed on the lock barrel, the hiss got much louder. After refitting everything back together, and making sure the o ring that goes around the lock barrel was properly seated, the hiss stopped and has never returned. I'm assuming it was just a natural escaping of gas from the fuel as it slowly evaporates. It certainly wasn't a huge rush of gas escaping.

The standard cars don't have a rollover valve like that Craig. That's a modification by the dealer....
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This is how it looks now