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S2 3B and ABY and RS2 ADU Boost Leak Testing (Draft)

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  • S2 3B and ABY and RS2 ADU Boost Leak Testing (Draft)

    The 3B and ABY-powered S2s and the ADU powered RS2s have a fairly simple turbo to intake system, as shown here as an AAN schematic (3B/ABY/ADU details obviously vary - be patient, 3B/ABY/ADU specific info to follow below) (NOTE: Hyperlinks are underlined - click for more info):



    However, there are at least six other systems that are connected to the 3B/ABY/ADU turbo system. These other systems include:
    1. The bypass valve system,
    2. The N80 Evaporative Emissions Control System,
    3. The Crankcase Ventilation system,
    4. The N75 Waste Gate Frequency Valve (WGFV) system.
    5. The Fuel Pressure Regulating Valve system.
    6. The N71 Idle Stabilization Valve (ISV)

    There are rubber and metal components of all four systems that have and/or will fail at some point, allowing boost pressure (and air) to go missing. This results in poor performance and, sometimes, a check engine code because the ECU recognizes that less air than expected showed up at the engine.

    The purpose of this post is to identify the most likely causes of the boost/air leak and how to find them.

    The possible sources of a boost leak, based on highest to lowest probablilty, include the following:

    1. The boost hoses from the turbo to the intercooler and from the intercooler to the throttle body, particularly hose from the intercooler outlet to the intake pipe that runs along the top side of the cam cover. This "Michelin Man" hose is corrugated and made of rubber. Oily vapours tend to condense inside the hose and lay in the valleys of the corrugations. This rots and weakens the rubber until the point where it splits, causing a massive boost leak. At that point you really don't need a boost leak test. This post is intended to help you find the leak before it is massive so you can replace the hose before it fails catastrophically.

    Here's a photo from AudiHeel(GoHeels) showing the way the rubber rots and eventually splits:




    2. The "Tee" hose where the N80 Evaporative Emissions Control System and Crankcase Ventilation system connect into the intake manifold. Here is one example of one such "Tee" hose with a split, upstream of the PCV system one-way valve (happens to be on an AAN but 3B/ABY/ADUs have the same idea and same part number)



    3. The other hoses and pipes between the turbo and the throttle body, including those cut or bent by over-zealous clamp tightening.

    Here is an example ABY turbo to intercooler hose showing the branch to the By-pass valve (BPV):



    Here is a photo of the rubber boot that connects the intake pipe that runs along side of the cam cover to the throttle body. It apparently sometimes gets old, soft and splits. Note that this photo also shows the branch from the boot that connects to the ISV. These two hoses constitute plugging locations C1 and C2 in the diagram below.



    Here is an example of the intake pipe to throttle body hose that shows a split just where the clamp is located. The owner of the RS2 in question, Mr. G said "What made this one very difficult was because the tear was at the bottom of the hose. When the hose was removed, visually looking at the hose didn't show the tear, we only found it by stretching the hose to see the tear."


    Photo courtesy of Mr. G

    4. Other components of the Crankcase ventilation system, including the one-way bleeder valve and the pressure regulating valve and any and all plastic, metal and rubber piping.


    Photos courtesy of Autohauz and ECS Tuning

    5. The N71 Idle Stabilization Valve (ISV) (plastic bits crack and leak) and the attendant hoses and pipes between the ISV and the back of the intake manifold.



    Here is an ISV valve showing leaking during a 3B/ABY/ADUboost test.


    Thanks to ?? for the photo.


    6. The Bypass Valve



    7. The N80 Evaporative Emissions Control System valve



    8. The N75 Waste Gate Frequency Valve and its attendant vacuum lines.

    9. The vacuum lines between the intake manifold and the Fuel pressure regulator and the Moisture Trap and The G71 Manifold Absolute Pressure (MAP) sensor (in the ECU)


    Here are four diagrams that contain the info needed to methodically think through the boost testing procedures and what you are looking for.

    The 3B/ABY/ADU intake tract from air cleaner to throttle body (note labels (A1),(B2), (C1) etc):



    The 3B Crankcase Ventilation system diagram (Note Items 4 and 6):



    The ABY (and ADU) Crankcase Ventilation system diagram (Note Items 3 and 20 (and 21))



    The N80 Evaporative Emissions System, he WGFV and BPV vacuum lines, and the vacuum/boost lines to the fuel pressure regulator, the moisture trap and the MAP sensor:



    Here is a schematic diagram that shows a boost test that focuses only on the boost hoses and intercooler between the turbo and the throttle body (happens to be an AAN but 3B/ABY/ADU are all the same, schematically) (Option 6 below):



    Testing for boost leaks involves introducing controlled pressure, i.e. 10 to 15 psi (0.7 to 1.1 Bar) from an air compressor into a non-running engine, with a pressure testing bung, such as shown in the diagram below and various other hoses plugged off (as appropriate to that test).

    Here is an example boost testing cap with an air hose fitting (could also be a metal Schrader valve) to introduce the air and then monitor with a pressure gauge.


    Photo courtesy of 4Driver4 (Tom M.)

    Having a spray bottle filled with a very soapy water solution to spray onto the suspect parts (bubbles = leaks) is useful (the leak might be small and it might not produce a noticeable sound)

    Here is a table that outlines the various boost testing options based on the above diagrams. Note: The table was set up to isolate certain components. Many people, most notably prj (dmitri) have suggested that the simplest method of boost leak testing that captures all the possibilities in one go is to place the pressure bung in "A1" in the diagram and disconnect the hose from the cam cover to "A3" and plug "A3", leaving the rest alone. This falls some where between test Option 1 and Option 3.



    There are probably some minor errors in the above that will be corrected after people make their comments and provide their suggestions.

    ADDITIONAL PHOTOS WELCOMED.

    Thanks to those who contributed photos and diagrams used in this post.

    AAN boost testing is already done but needs to be revised and converted to vBulletin format for here.

    The 200 20VT boost testing is out for review (could have been combined with this one but I posted it on a North American forum in vBulletin format (we got 3B 200 20VTs but no S2s) so I thought I might as well port it over here intact).

    /The staff at STFA.
    Last edited by UrS4boy; 18 August 2013, 19:47.
    RS2'd 93 UrS4 5 spd sedan
    94 UrS4 V8 6 spd manual avant

  • #2
    Nice work, as ever, Dave.

    Another top boost leak culprit is the short hose at the throttle body. They quite often split underneath. But they certainly used to be reasonable cheap to replace.

    I 'upgraded' my 3B Michelin Man/Accordion hose to a stock ABY hose. It just needs trimming to length at the intercooler end. It eliminates a couple of unnecessary joints, and I am sure it must flow better.
    It can be a cheap modification with all the ABY boost hoses being traded for silicone hoses.
    SS

    Comment


    • #3
      Originally posted by 4WheelDrifter View Post
      Nice work, as ever, Dave.
      Another top boost leak culprit is the short hose at the throttle body. They quite often split underneath. But they certainly used to be reasonable cheap to replace.
      I 'upgraded' my 3B Michelin Man/Accordion hose to a stock ABY hose. It just needs trimming to length at the intercooler end. It eliminates a couple of unnecessary joints, and I am sure it must flow better.
      It can be a cheap modification with all the ABY boost hoses being traded for silicone hoses.
      Thanks. (I try )

      So the hose that I have labeled with the "C1" connection to the throttle body leaks? Anybody with a photo of one that has split (or even an unsplit one) that I can include in the post?

      It is curious (as in "wierd") why the 3B had a multi-part hose/pipe between the intercooler and the intake pipe that runs along the cam cover and the ABY and ADU just had one corrugated/bellows/Michelin Man hose.

      I can imagine 3B people "inheriting" ABY hoses when ABY people go to silicone hoses.
      RS2'd 93 UrS4 5 spd sedan
      94 UrS4 V8 6 spd manual avant

      Comment


      • #4
        Originally posted by UrS4boy View Post
        ...So the hose that I have labeled with the "C1" connection to the throttle body leaks? Anybody with a photo of one that has split (or even an unsplit one) that I can include in the post?
        I am trying to go to bed (12:30 AM here) but I managed to find this photo that I will include in both the S2 3B/ABY and RS2 ADU post and the 200 20VT 3B post when I get up in 7 hrs or so. Where exactly does it split?

        This one shows the branch to the ISV valve as well:

        RS2'd 93 UrS4 5 spd sedan
        94 UrS4 V8 6 spd manual avant

        Comment


        • #5
          Updated with a couple of new photos:

          "Here is a photo of the rubber boot that connects the intake pipe that runs along side of the cam cover to the throttle body. It apparently sometimes gets old, soft and splits. Note that this photo also shows the branch from the boot that connects to the ISV. These two hoses constitute plugging locations C1 and C2 in the diagram below.

          "

          and

          "Here is an ISV valve showing leaking during a 3B/ABY/ADUboost test.


          Thanks to ?? for the photo. "
          RS2'd 93 UrS4 5 spd sedan
          94 UrS4 V8 6 spd manual avant

          Comment


          • #6
            Looks good. Just need some stock ABY / ADU pictures to complete it, I'm sure someone will be able to help.

            Understanding the inlet and breather circuits took me a long time, as something like this wasn't readily available. I have to say, it was a good few years before I was confident what was what enough to start with the breather system upgrades.

            It may be a nice thing to do something on catch tanks using your diagrams, such as this one:-



            Basic tank connects to item xx etc. Perhaps for another thread though...
            Cheers'en, AndyC
            1994 ABY Coupe - Projekt Alpinweiss

            Comment


            • #7
              Originally posted by UrS4boy View Post
              I am trying to go to bed (12:30 AM here)
              Well Dave understanding that it was late in beautiful Canada and you were tired...
              But theres no way you can stretch the canonic 24.00 hours!

              That said, fantastic write up as usual!

              Thanks Stefano
              http://www.audisportclub.com/

              http://www.s2forum.com/forum/vbgoogl...227295&zoom=16

              Comment


              • #8
                Originally posted by Rusty View Post
                Looks good. Just need some stock ABY / ADU pictures to complete it, I'm sure someone will be able to help. ...It may be a nice thing to do something on catch tanks using your diagrams, ...Basic tank connects to item xx etc. Perhaps for another thread though...
                More pertinent 3B/ABY/ADU photos? Absolutely. Yes PLEASE. Anyone. I am doing this for you guys, it can only be made better with your input.

                As for the catch can, I have previously suggested this schematic layout, i.e. catch can AFTER the pressure regulating valve with the discharge piped into the AAN/ABY/ADU cam cover or 3B pipe and then into the MAF to turbo hose, as per stock:

                RS2'd 93 UrS4 5 spd sedan
                94 UrS4 V8 6 spd manual avant

                Comment


                • #9
                  Originally posted by veneto rs2 View Post
                  Well Dave understanding that it was late in beautiful Canada and you were tired... But theres no way you can stretch the canonic 24.00 hours! That said, fantastic write up as usual! Thanks Stefano
                  Thanks Stefano. I guess I should have converted the time to 00:30 for you 24:00 clock people. (We use 12 hr clock so 00:30 = 12:30 AM). Too late for old guys.
                  RS2'd 93 UrS4 5 spd sedan
                  94 UrS4 V8 6 spd manual avant

                  Comment


                  • #10
                    Good thread!

                    Always had a bit of moist at the T-piece, after cleaning it with brake clean a few times. Didn't know it was a common one to fail... ordered one

                    Comment


                    • #11
                      Originally posted by UrS4boy View Post
                      Where exactly does it split?
                      Where you can see where the hose clip has marked the hose at the TB end, IIRC it splits near there where the rib is.
                      SS

                      Comment


                      • #12
                        Originally posted by 4WheelDrifter View Post
                        Where you can see where the hose clip has marked the hose at the TB end, IIRC it splits near there where the rib is.
                        Thanks for the input. This should help 3B/ABY/ADU track down the more mysterious boost leaks.
                        RS2'd 93 UrS4 5 spd sedan
                        94 UrS4 V8 6 spd manual avant

                        Comment


                        • #13
                          This should be a sticky. Very useful information all in one place. Thanks UrS4boy
                          1995 Audi S2 Avant

                          Comment


                          • #14
                            Now Stuck.
                            The Perfectionist
                            sigpic
                            Audi Class Concours winner Stoner Park 2014, ADI Concours D'Elegance Class Winner 2008, Runner up 2014. Winner, S2Forum Show'n'Shine Billing 2006 & 2008.

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                            • #15
                              Traced and fixed a boost leak this morning- might be of assistance to someone else
                              The little pipe underneath the intake had to be replaced - pics attached. Had to remove the air intake pipe that runs along the engine and throttle body to get to the pipe

                              Symptoms were smoke from the exhaust at wot, huge puff of smoke when starting sometimes, fuel smell in the car and higher than usual fuel consumption. She was obviously running too rich.



                              Sent from my iPhone using Tapatalk

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