Fuel Filler Cap Cork Seal
Discussion
I bought one of these a couple of years back when I spotted this while browsing the equivalent parts thread 
'The petrol cap cork sealing washer is the same as that used on old Triumph motorcycles. It's a 2½" cork seal.
Part No is 82-4048 and they can be bought from www.btinternet.com/~hawkshaw.motorcycles/triumph8....
or I got mine from eBay believe it or not!!
The fit is very tight with the new seal, but I expect this to loosen as the cork gets squashed.'
'The petrol cap cork sealing washer is the same as that used on old Triumph motorcycles. It's a 2½" cork seal.
Part No is 82-4048 and they can be bought from www.btinternet.com/~hawkshaw.motorcycles/triumph8....
or I got mine from eBay believe it or not!!
The fit is very tight with the new seal, but I expect this to loosen as the cork gets squashed.'
aide said:
Hi!
The Fuel Filler Cap Seal on my car has perished.
Does anyone know what to replace it with?
The difference in performance when there is no fuel pressure is astonishing.
Any help would be greatly appreciated
Aide.
Just curious as to why the cork seal would impact the fuel pressure?The Fuel Filler Cap Seal on my car has perished.
Does anyone know what to replace it with?
The difference in performance when there is no fuel pressure is astonishing.
Any help would be greatly appreciated
Aide.
The bottom of the tank feeds the LP side of the fuel-pump which then pressurises the fuel rail up to the regulator. The regulator then bleeds-off the excess back to the tank.
If the cap is letting air in, it shouldn’t affect the HP circuit at all… should it?
I have a feeling I’m about to learn something here.
Do you not notice the hissss when you open the cap to fill up at a petrol station when the tank is empty?
The whole system is pressurised.
The cap does not let air in. It is the opposite.
There is a breather line. It comes from the fuel rail and runs all the way back to the fuel tank. It allows the tank to breathe.
Inside the breather line there is a metal bung with a 2mm hole in it. It allows the tank pressure to equalise while the fuel pump can maintain the fuel pressure to feed the injectors.
When the breather line is changed, the bung is often overlooked as it's impossible to know its there unless you are aware of it. It is very important.
A damaged cork seal on the filler cap means that the fuel pump can't maintain fuel pressure to feed the injectors.
So when you wide open the butterfly's there's not enough pressure to proportionally feed fuel.
Best way to demonstrate is to simply go for a drive with no seal in the cap.
The difference is unbelievable.
Check if you have the bung as well
The whole system is pressurised.
The cap does not let air in. It is the opposite.
There is a breather line. It comes from the fuel rail and runs all the way back to the fuel tank. It allows the tank to breathe.
Inside the breather line there is a metal bung with a 2mm hole in it. It allows the tank pressure to equalise while the fuel pump can maintain the fuel pressure to feed the injectors.
When the breather line is changed, the bung is often overlooked as it's impossible to know its there unless you are aware of it. It is very important.
A damaged cork seal on the filler cap means that the fuel pump can't maintain fuel pressure to feed the injectors.
So when you wide open the butterfly's there's not enough pressure to proportionally feed fuel.
Best way to demonstrate is to simply go for a drive with no seal in the cap.
The difference is unbelievable.
Check if you have the bung as well
Yeah, the breather hose bung with the 2mm hole in it, I found out about by accident when I was ordering new hoses a few years ago.
Someone at Raceproved mention it when I was ordering a few bits from them.
They actually didn't know the diameter of the hole and went off and found out, then called me back a few days later. Top chaps.
I made the bung by cutting a bolt, drilling a 2mm hole in it and cutting a slot in the top so I could screw it 10cm inside the breather line.
Someone at Raceproved mention it when I was ordering a few bits from them.
They actually didn't know the diameter of the hole and went off and found out, then called me back a few days later. Top chaps.
I made the bung by cutting a bolt, drilling a 2mm hole in it and cutting a slot in the top so I could screw it 10cm inside the breather line.
phillpot said:
A more sophisticated system than earlier cars.
Yes, when you couple that with the closed loop real time adaptive fuel map that auguments the base map, which self adjusts by using feedback from the narrow band lambda sensors, it really is quite beautiful. I think if there was a way to add variable length induction, like 993 VarioRam, it would be really wonderful.
https://en.m.wikipedia.org/wiki/VarioRam
Thanks for taking the time to explain Aide, and that’s very interesting about the return pipe.
So, if the fuel pump pulls fuel from the tank, delivers it to the injectors and returns only a fraction of it back (through the breather pipe as you describe), then the breather pipe must also be adding some air back into the tank (to equalize the pressure and avoid the tank collapsing).
I’m not sure whether the system runs a bit of vacuum in the tank or positive pressure (the whoosh upon opening the filler cap could be air rushing in, or out).
Either way, I’m still not understanding how having an open (or leaky) cap, would make any difference to the pressure in the fuel rail (the high pressure side of the fuel pump, up to the regulator at the back of the rail).
:-(
So, if the fuel pump pulls fuel from the tank, delivers it to the injectors and returns only a fraction of it back (through the breather pipe as you describe), then the breather pipe must also be adding some air back into the tank (to equalize the pressure and avoid the tank collapsing).
I’m not sure whether the system runs a bit of vacuum in the tank or positive pressure (the whoosh upon opening the filler cap could be air rushing in, or out).
Either way, I’m still not understanding how having an open (or leaky) cap, would make any difference to the pressure in the fuel rail (the high pressure side of the fuel pump, up to the regulator at the back of the rail).
:-(
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