Audi A6 2.4 petrol. fuel sensor problem!

**callamarn** · 21-11-2009,11:29 PM

Hi everyone,
Just bought an old audi A6, 1998 model which has a fault in the fuel line area. The fuel gauge reads empty all the time and the fuel tank seems to pressurise as I can here a his from the fuel filler cap. The car runs perfectly. Anyone have any ideas where to start?

**Peter D** · 22-11-2009,08:48 AM

Under the rear seat drivers side is an inspection cover for the fuel tank pump and gauge sensor. Bepending on the model you may have two sensors. You need to check the connections and measure the resistance with a meter. The tank should not pressurise so you may have a blocked breather pipe. Regards Peter

**callamarn** · 22-11-2009,10:21 AM

Thanks Peter. Will check that out.

**nskeates** · 24-11-2009,08:18 AM

I also have a hissing noise that comes from around the fuel filler cap, same model and year as well. car runs fine. Could anybody tell me what needs to be looked at as car going in to garage next week for a thermostat change and cam gasket, so they could look at the hissing as well.

thanks

**Peter D** · 24-11-2009,10:09 AM

There is a vent control valve that is normally open unless the car is inclined by 45 degrees. It is called a garvity valve and vents the tank all the way forward to the Charcoal Evap Filter in the front wing.
This valve can stick. If you PM me with your email address I'll send you a drawing. Regards Peter

**nskeates** · 24-11-2009,10:13 AM

Thanks Peter,

This is related to the tube which is just under the car near the drivers door. i have been getting funny sounds from that but did not realise they where related. You emailed me the pictures of that and i haven't got around to checking due to the weather. Will get garage to look at it. does it do any harm if this vavle is stuck ? ie can it be left a week ?

thanks

**Peter D** · 24-11-2009,10:35 AM

A sticking gravity valve can cause feul starvation. A sticking evap valve can cause a mixture/feuling problem at lower rpm and at idle. Regards Peter

**nskeates** · 24-11-2009,10:39 AM

thanks Peter,

so from what i understand there are 2 different valves on my car that could be playing up by the noises i'm getting, are they both related in any way ? My idle is a little rough.

thanks

**Peter D** · 24-11-2009,12:17 PM

The Charcoal evep filter obsorbs petrol fumes when the engine is turn off and from the tank. When you start the car an evep solenoid opens ( pulses ) and sucks in fresh air through the filter and uses it in the engine. On cold days this can be pulsing for 10 to 15 minutes. If this valve stick open and the engine is hot, air enters the ststem and can cause the rough idle. This can also cause the sucking noise mentioned on here as this should be short pulses not continuos and in wet weather water can get sucked up the pipe. The tank gravity valve is up near to top of the filler tube. This allows free movement of air in and out of the tank unless the car has an accident and turns over the gravity valve closes and avoids fuel slippage. The vent pipe from the gravity valve it fed to the Charcoal filter, if the soleniod has failed open guess it can suck the gravity valve closed thus the hiss. Regards Peter