Question about 2002 Audi TT

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Fuel tank pressuring

When fuel cap is removed the tank vent a lot of air and is running rough at low speed

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Problem with evap system. Charcoal cannister may be full of liquid gas, if so drain or replace. In the future, do not top off tank when filling.

Posted on Oct 22, 2013

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Posted on Jan 02, 2017

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Acts like its running out of fuel

p { margin-bottom: 0.25cm; line-height: 120%; } My Car Drives and Then Cuts Out. It Restarts After a Couple Of Minutes
Your car starts and drives okay and then suddenly, it splutters and slows down and then picks up speed again. Or it slows down, splutters and then dies. The fault is erratic: some days the car drives perfectly at all speeds and other times, the symptoms reappear. There's no warning lights on the dashboard. Sound familiar?

It could be caused by a sensor failure, yes, but the symptoms are also classic signs of :
1. A partial vacuum in the fuel tank
2. Blocked fuel filter
3. A failing fuel pump.

Partial Vacuum
Fuel tanks are vented to atmosphere. Air should be able to get into the tank. To achieve this the tank has a small tube which probably appears somewhere underneath the car in the vicinity of one of the rear wheels, or the fuel filler cap itself has a small vent hole in it.

If that vent tube becomes blocked by debris thrown up by the wheels or the vent in the filler cap becomes blocked, a partial vacuum builds up inside the tank. As the fuel level drops the vacuum 'holds it up' and restricts fuel flow to the engine.

A quick check is, when the car begins to splutter and die, is to quickly remove the fuel cap. If you hear air rushing into the tank you know that there was a partial vacuum inside.

Fuel Filter
A blocked fuel filter causes the same symptoms. However, you won't hear air rushing into the fuel tank when the filler cap is removed. There's no way of dealing with a fuel filter other than by replacing it with a new one.

A lot of fuel filter problems are caused by corrosion - that's corrosion from the tank and filler pipe itself. It blocks the fuel supply. It mainly applies to older cars but as the fuel filter is a service item it makes sense to change it every couple of years anyway.

Failing Fuel Pump

The most classic symptom of all.

The way to test a fuel pump is by disconnecting the fuel line that runs into the engine bay. Get somebody to turn the ignition on for you - and fuel should literally spurt out. Not trickle or dribble .. it should spurt out.

However, herein lies a problem. Fuel pumps that are nearing the end of their lifespan still work - it's those erratic moments when they stop pumping your car splutters and slows down. An erratic, failing fuel pump can still throw fuel out of a disconnected fuel line. You're no further forward.

Other than pressure testing the fuel supply a workshop can not do much else that you can not do. They certainly won't remove the fuel pump from the tank and test it. They would simply replace it. You would have to do the same if you suspected the fuel pump was failing and causing the problems.

Usually, the fuel pump is situated in the fuel tank. Access is via an inspection cover that is screwed to the top and accesible from inside the car (usually).
Some vehicles have two fuel pumps. There is the pump in the tank which lifts the fuel into the fuel line. The second fuel pump - either fitted underneath the vehicle or in the engine bay - pushes the fuel up to the injectors.

In such twin-fuel pump systems it is usually the in-tank lifter pump that fails, simply because it is the one that does the hard work.

Oct 15, 2015 | 2003 Dodge Caravan

1 Answer

No tank pressure. runs rough. ?

Most tanks now have a vent tube, a dirt Dobbler might of blocked it.

Feb 27, 2015 | 1999 Toyota 4Runner

1 Answer

Buildup gas tank pressure I the cap off hear the fumes pressure come out

run the fault codes and look for purge valve and canister problems as the tank is not venting correctly

Feb 10, 2015 | Cars & Trucks

1 Answer

Landrover discovery idles rough when hot but idles good when fuel tank is low

Hi have you made sure the fuel tank is vented? or if the vent is blocked as i know of a couple of these that have done a similar thing, the fuel cap vent got blocked and the tank was under a lot of pressure causing problems in the idle, worth a try anyway

Apr 08, 2012 | 1996 Land Rover Discovery

1 Answer

After traveling, there was high air pressure in the fuel tank? is it normal?

Are you sure is was high air pressure and not vacuum? Most modern automobiles have fuel tank purge systems which will place the fuel tank under low pressure (or vacuum). If you remove the fuel cap immediately after travelling a long distance or while the engine is still running, it could be normal to hear a "hissing" sound when removing the cap as the pressure in the tank will equalize when the cap is removed.

Apr 06, 2012 | Toyota RAV4 Cars & Trucks

1 Answer

My problem is a come and go thing. At times i can get no more than 50 mph when this has happened I have noticed when I remove the fuel cap theres is a lot of pressure released or it is air taken in. It is...

The tank breather is blocked.
The tank needs outside air to enter as the fuel is pumped out, if this is not happening, the tank is pulled into negative pressure and this will prevent the fuel from being drawn at the correct rate.
The tank vent is a pipe from the tank which is then usually attached to the chassis and nothing else. It may have some form of vapour lock on the end to prevent gas fumes from escaping and forming a fire risk. This is the pipe that is blocked or the vapour lock is blocked. Locate it and remove it to clean it but DONT leave the vapour lock off the pipe when you refit it..
Some fuel tanks are vented through the fuel cap and don't have this pipe so check and make sure that the correct cap is fitted. You can also drill a very small hole through the top of the cap which may allow air to enter the tank although this is not advisable as there would be no vapour lock.

Jan 21, 2011 | Dodge Ram 3500 Cars & Trucks

2 Answers

Fuel tank holds extremely hi pressure after changing out fuel pump on a 2000 silverado 5.3 engine.the more distance you drive the higher the pressure gets in tank.

You may be referring to the lowering of pressure in your fuel tank. As fuel is used, the pressure in the fuel tank drops to prevent vapours in the tank escaping to atmosphere. Ths is to comply with emission standards. The further you drive, the lower the pressure. When you remove the tank cap, air rushes in which makes you think it's coming out.

Mar 22, 2010 | 2000 Chevrolet Silverado 1500

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