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Please read through all of the instructions here and make sure you understand them before attempting this procedure!

You are about to do work on your car's fuel system, which can be hazardous to your health and your vehicle's. Please read the following warnings before proceeding:
  • No smoking!
  • No drinking!
  • No eating!
  • No power tools, including vacuum cleaners.
  • No halogen lights. (Halogen lights create a lot of heat, and could create a fire hazard around fuel)
  • No compressed air. (Compressed air can generate static electricity and sparks)
  • Before starting work, clean the general area you'll be working in of dust, dirt, and grease.
  • Have a place to put used components and old gasoline. Keep in mind that used components may dribble old gas wherever you put them down, so don't put them on something nice (like your spouse's car).
  • Cover open components such as fuel lines and hoses with a clean rag or dust cap if they will be open for more than a minute or so. Use your own discretion here; you just want to keep stuff out of them. Don't use tissues or fluffy towels that could leave lint.
  • Only install new, clean parts.
  • Do not remove replacement parts from their packaging until immediately before they are to be installed.
  • Do not use parts that have been stored without packaging (i.e. in a toolbox).
  • Don't attempt to start the engine while any fuel lines or components are disconnected.
    This procedure is written for an A6, but will work for any car that has the fuel filter under the hood. This eliminates 80/90, Coupe, and possibly Cabriolet and A4 cars.

    This is a pretty easy job, but it requires a bit finesse. First off, decide where you are going to do the job. Park the car and leave it off overnight. This will allow the fuel system to slowly lose pressure, so that when you begin to loosen the fuel lines, gas won't be spraying all over.

    Definitions and Acronyms

    • EVAP: EVAPorative emissions control. An emissions control system that controls emissions of fuel vapors from the fuel system.
    • MAF: Mass Air Flow sensor. The MAF sensor senses the amount of air moving through the intake to accurately meter fuel injection.

    Tools Required:

    • 10mm open end wrench
    • 14mm open end wrench
    • 17mm open end wrench
    • 19mm open end wrench
    • Large adjustable wrench
    • 10mm 6-point socket
    • 6 inch (or so) extension for socket
    • Your favorite ratchet drive
    • Small needle nose pliers
    • Felt tip pen or magic marker
    • Shop rags that can get gas all over them
    • Paper towels
    • Small jar (at least 2 cups) to hold old gas
    • Small container to drain fuel filter in (you might need to make multiple 'trips' with this)

    Parts Required:

    • Fuel filter
    • Aluminum or copper crush washers for filter outlet


    1. Open the hood and locate the fuel filter.
    2. Clean the general area where the fuel filter is with some paper towels. Lay some paper towels on the black plastic shelf in front of the windshield, and put your tools there.
    3. Disconnect the electrical connectors from the EVAP pressure sensor and EVAP frequency valve.
    4. Remove the EVAP frequency valve and its rubber holder from their mounting bracket by pulling them towards the firewall.
    5. OK, here comes the gas. You should only get a few drops if you let the car sit overnight like I told you to. Put some paper towels under the rear filter flare nut, and loosen the nut using your 14mm and 19mm open end wrenches. The 19mm wrench is to prevent the filter from turning, and the 14mm wrench is to actually twist. Don't remove the nut completely, just loosen it.
    6. Remove the filter clamp using your 10mm socket and ratchet. The dome nut closer to the engine is a bit hard to remove, but removing the EVAP frequency valve should have given you enough 'wiggle room' to get it out. Don't worry about the brass inserts right now, unless they are easy to remove.
    7. Now finish unscrewing the rear (inlet) fuel line. Pull the inlet fuel line out of the fuel filter (adapter) to make sure that it's free. Don't abuse the flared end. Don't bend the fuel line. Use some finesse!
    8. Lift the fuel filter off the stud mounts. Watch those brass inserts! You might need to remove them with your small needle nose pliers.
    9. Place your old gas collection container under the rear of the fuel filter and hold on to it with your left hand. With your right hand, lift the filter and tip (rotate) the front of the filter up to drain the gas out of the filter and in to your container. That piece of rubber hose on the output line is handy, isn't it!
    10. Finish draining the filter and set it down gently. Use some paper towels for a cradle if you want.
    11. Get the old gas out of the general area.
    12. Now use the adjustable wrench and 17mm open end wrench to loosen the banjo bolt on the front of the filter.
    13. Use the adjustable wrench to prevent the filter from rotating, and use the 17mm wrench to actually twist. When the fitting is loose enough to rotate by hand, put the tools down. Finish removing the fitting by hand, and make sure that you don't lose either of the two washers! There is a washer on both sides of the banjo fitting.
    14. Place the washers and banjo bolt in a safe place where they won't get lost.
    15. Remove the fuel filter from the engine bay and drain any fuel that is left in it.
    16. Clean the old filter with some paper towels.
    17. Wash your hands and take a break, you've earned it!
    18. Take the new filter out of the box and set it next to the old filter. Use your marker to mark the position of where the mounting bracket should go on the new filter.
    19. Use a 10mm open end wrench to loosen the mounting bracket from the old filter and remove it.
    20. Use the 10mm open end wrench to remove the adapter and copper crush washer from the old fuel filter. Add them to your 'collection.' You may even need them some day!
    21. Clean the mounting bracket a bit and place it on the new filter. Make sure that the bracket orientation is correct, with the mounting holes pointed towards the front (inlet) of the filter. Place the bracket in between the marks you made and tighten it with a 10mm open end wrench.
    22. Remove the dust caps off the ends of the new filter.
    23. Place the fuel inlet tubing in the filter and hand tighten the flare nut.
    24. Reconnect the banjo fitting and hand tighten. Don't forget the crush washers!
    25. Place the fuel filter on the mounting studs while making sure that the fuel line on the banjo bolt is pointed at approximately 4 o'clock. The outlet hose needs to be oriented below the middle of the filter body.
    26. Place the brass inserts into the filter mounting bracket using needle nose pliers. You can just fit your fingers in there if you're young and flexible.
    27. Place the washers and nuts on the mounting studs.
    28. Finish tightening the flare nut on the back of the filter using 19mm and 14mm open end wrenches.
    29. Tighten the mounting bracket nuts with the 10mm socket and ratchet. Don't tighten the nuts till the studs snap off or the nuts strip, use some finesse.
    30. Finish tightening the banjo bolt using the large adjustable wrench and 17mm open end wrench.
    31. Place the EVAP frequency valve on its mounting bracket.
    32. Re-connect the wiring harness connectors for the EVAP frequency valve and EVAP pressure sensor.
    33. Now place a couple of rags under the front and rear fuel lines at the filter.
    34. Wash your hands and get your car key.
    35. Now remember the filter doesn't have any gas in it. Turn the key until you hear the fuel pump coming on (the 'on' position of the key, before 'start.'). Turn the key off and then repeat.
    36. Now start the engine. You may need to crank for a bit to get the rest of the air out of the system. Don't crank for more than 10 seconds -- if you need to crank longer, wait for 10-20 seconds before trying again.
    37. Only run the engine for 5 seconds or so. Turn it off!
    38. Check for fuel leaks at the filter. Touch the lines, feel all around them, and make sure that they are dry.
    39. If needed, tighten the fuel lines a bit more. You didn't forget to put both washers on the banjo bolt, did you?
    40. Do a 5-second re-test if needed.
    41. Start the engine and let it run for a few minutes.
    42. Check for leaks again.
    43. Turn off the engine.
    44. Remove the rags and your tools, and clean up. Wash your hands again ... you're done!

    Procedure by Seattle Scott, who takes no responsibility for your actions. Questions/comments about the procedure go to him.


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