Fuel Pump

[Malbec]

Driving today the fuel pump started sqealing. I looked in the history folder and my car is now on its 3rd fuel pump. The car has only done around 84k miles and the pump was last changed about 8k ago at audi. When i start the car it sounds like the tank is compressing a bit and air rushes in when i remove the fuel cap. It seems like the tank is not venting properly and maybe that is why the fuel pumps keep failing so quickly. How do i unblock the venting system or can i just drill a small hole in the plastic fuel cap?

Car is 1991 Audi 100 C4 2.3 (AAR)

[BIGGYIN]

On my KV K-Jet,I'm sure the tank is surposed to be pressurised?
I think cars with carbs,have a vented fuel tank?

[Malbec]

Originally Posted by BIGGYIN

On my KV K-Jet,I'm sure the tank is surposed to be pressurised?
I think cars with carbs,have a vented fuel tank?

Is it meant to be a vacuum though? The air rushes in when I remove the filler cap, not rushes out as if it were pressurised. I can hear the metal tank deform slightly when I start the car, which I don't think it should.

I think you are right that they are not vented, my mistake, but it should maintain constant slight pressure in the tank through the charcole canister. So if i've got a vacuum, then I guess the charcole is blocked or the pipework? Would I need a new charcole canister?

Cheers, john

[BIGGYIN]

Mine doesn't have any charcoal,so don't really know?

Someone else should come up with, abetter answer?

[Malbec]

Originally Posted by BIGGYIN

Mine doesn't have any charcoal,so don't really know?

Someone else should come up with, abetter answer?

Ok, cheers anyway.

Looking on the net I think there is something called purge valve somewhere that could be broken blocked, no idea where it is though. I've read that the charcole conister can be removed, but i don't know how. Want to get this fixed quickly before it knackers another fuel pump or damages the tank.

[msh]

Your car has fuel tank ventilation system consisting of non return valve somewhere around fuel tank, vent line, charcoal filter and valve. Fuel injection control unit is supposed to operate that valve in a way to keep tank pressure slightly below atmospheric - by keeping valve closed at idle [when there's low pressure in intake], cycling it at moderate loads and opening it when throttle is floored. Since I haven't experienced such a problem, I can only guess that it is caused by valve - I don't know if it's closed or open when power is applied, if it's closed, then one broken wire might be enough to cause this problem. I presume that in C series cars the valve is in the same location as in B series cars - attached on top of intake boot, with two hoses attached, one going to charcoal filter somewhere in right wing, another to throttle body. Take it off, inspect wires, test by sucking if it's open with no power applied, apply power with two wires from battery to see if it closes etc.

[Malbec]

Originally Posted by msh

Your car has fuel tank ventilation system consisting of non return valve somewhere around fuel tank, vent line, charcoal filter and valve. Fuel injection control unit is supposed to operate that valve in a way to keep tank pressure slightly below atmospheric - by keeping valve closed at idle [when there's low pressure in intake], cycling it at moderate loads and opening it when throttle is floored. Since I haven't experienced such a problem, I can only guess that it is caused by valve - I don't know if it's closed or open when power is applied, if it's closed, then one broken wire might be enough to cause this problem. I presume that in C series cars the valve is in the same location as in B series cars - attached on top of intake boot, with two hoses attached, one going to charcoal filter somewhere in right wing, another to throttle body. Take it off, inspect wires, test by sucking if it's open with no power applied, apply power with two wires from battery to see if it closes etc.

Cheers mate, that is a great guide to the system and exactly what I needed to know. I will go have a look and test the valve later. If I can't find a problem or blockage, would it be ok to just drill a very small hole in the plastic filler cap, as a work around?

[msh]

Better no.