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Turbo to Intercooler Hose Routing on VW T4 Transporter 2.5 TDi 2003 with EGR Pump

Dalton33 94557 21
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How should the vacuum hoses be routed on a VW T4 2.5 TDI with an EGR valve and vacuum pump?

For the ACV/AJT/AUF/AYY/AYC vacuum layout, connect the hoses as 8→1, 6 and 3→2, 7→9, and 4→10; if needed, swap 6 with 7 for the valve that closes the intake flap during engine shutoff [#6817835] No. 12 is the vacuum line from the vacuum pump to the brake servo, and No. 8 gets a short hose with a small air filter attached [#6797546] The small grey sensor takes one hose from the vacuum supply (a tee can be used) and the other hose to the intake closing flap on the manifold/black box [#6797546]
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  • #1 6777821
    Dalton33
    Level 10  
    Posts: 10
    Rate: 33
    Hello,
    I have a problem with connecting the hoses coming from the turbo to the... I have a problem with connecting the hoses coming out of the turbo to... exactly where they should go in the version I have under the intercooler there is an EGR with an attached pump (please see photo). Please help and thank you in advance.
    Attachments:
    • Turbo to Intercooler Hose Routing on VW T4 Transporter 2.5 TDi 2003 with EGR Pump egrValve.jpg (51.79 KB) You must be logged in to download this attachment.
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  • #2 6779394
    Anonymous
    Anonymous  
  • #3 6793388
    Dalton33
    Level 10  
    Posts: 10
    Rate: 33
    Hello,
    I know there is a difference depending on the colour of the TDI lettering mine is all silver otherwise I don't know how to check the engine power unless someone can tell me how to check it.
    Greetings
  • #4 6793442
    trans-serwis
    Level 39  
    Posts: 4854
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    The three-letter engine symbol on the pasteboard above the air filter.
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  • #5 6793792
    Anonymous
    Anonymous  
  • #6 6793914
    Dalton33
    Level 10  
    Posts: 10
    Rate: 33
    Thank you for the quick answer,
    Apart from the place above the air filter, where else can you find this three-letter symbol? I just had this part replaced from another transporter so I'm not sure if it's OK. Unless I'm looking wrong, is the paste or is it the black insulating material between the bumper and filter?
  • #7 6793937
    Anonymous
    Anonymous  
  • #8 6795243
    Dalton33
    Level 10  
    Posts: 10
    Rate: 33
    Hello,
    I think I have finally found this three letter symbol it is HBH located behind the injection pump on the engine block.
    Greetings and please help
  • #9 6796823
    Dalton33
    Level 10  
    Posts: 10
    Rate: 33
    Hello again,
    I know it sounds strange but I'm already sure it's the ACV, can I ask for a complete diagram of how all the vacuum hoses should be connected, i.e. those from the plastic hose that goes from the servo to the vac pump, then at the top it looks to me like there are three outlets, there's also one coming out of the EGR and there's a small grey sensor from which there are also two hoses coming out.

    Best regards and thanks in advance for your help.
  • #10 6797546
    Anonymous
    Anonymous  
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  • #11 6801289
    Dalton33
    Level 10  
    Posts: 10
    Rate: 33
    Thank you very much for your answers.
    But just to be 100% sure because I am really a beginner I am attaching the original pictures from my engine, can I ask for help like.
    connect valve 1 to 5 etc.
    In my version there is also a small valve sticking out from the wall behind the engine visible in the attached photos no.8
    Greetings
    Attachments:
    • Turbo to Intercooler Hose Routing on VW T4 Transporter 2.5 TDi 2003 with EGR Pump SzaryCzujnik.jpg (28.92 KB) You must be logged in to download this attachment.
    • Turbo to Intercooler Hose Routing on VW T4 Transporter 2.5 TDi 2003 with EGR Pump SciankaZaSilnikiem.jpg (20.11 KB) You must be logged in to download this attachment.
    • Turbo to Intercooler Hose Routing on VW T4 Transporter 2.5 TDi 2003 with EGR Pump PrzewodSerwoVacum.jpg (20.94 KB) You must be logged in to download this attachment.
    • Turbo to Intercooler Hose Routing on VW T4 Transporter 2.5 TDi 2003 with EGR Pump Pompka.jpg (22.57 KB) You must be logged in to download this attachment.
    • Turbo to Intercooler Hose Routing on VW T4 Transporter 2.5 TDi 2003 with EGR Pump EGRzawor.jpg (12.67 KB) You must be logged in to download this attachment.
  • #12 6801651
    fermik
    Level 15  
    Posts: 67
    Help: 14
    Rate: 63
    Dalton33 wrote:
    .
    I know this is going to sound weird but I'm already sure it's ACV or I can


    At last this sounded correct and something can be answered.
    I attach a picture of the vacuum system for engines
    2.5ltr. diesel eng.: ACV,AJT,AUF,AYY,AYC
    Turbo to Intercooler Hose Routing on VW T4 Transporter 2.5 TDi 2003 with EGR Pump .

    (corrected)

    There is free access to similar images at
    http://www.vagcat.com after free registration on the parallel forum.
  • #13 6801759
    Dalton33
    Level 10  
    Posts: 10
    Rate: 33
    Well, yes, but again I emphasise I am a complete beginner and from this diagram it seems to be for all versions, which for AVC I have no idea again please how is it possible to describe the connection according to the attached pictures above e.g..
    1 connect to 8 etc.
    Best regards
  • #14 6801821
    trans-serwis
    Level 39  
    Posts: 4854
    Help: 297
    Rate: 2253
    It couldn't be clearer. If that's not enough then give the car to a mechanic.
  • #15 6804388
    Dalton33
    Level 10  
    Posts: 10
    Rate: 33
    Can I ask someone knowledgeable to take a look at the pictures I have uploaded above and tell me which valve should be connected to which.
    Thank you in advance
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  • #16 6806830
    Anonymous
    Anonymous  
  • #17 6806879
    trans-serwis
    Level 39  
    Posts: 4854
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    Rate: 2253
    He will definitely not go.
  • #18 6806928
    Jacek79
    Level 37  
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    and the carburator is good?
  • #19 6808681
    Dalton33
    Level 10  
    Posts: 10
    Rate: 33
    I can see that most of the guys on here have gained their level from writing stupid and hopeless stories, if I could I would drive to a mechanic but I can't so the next time you think about why someone comes on the forum for help because no one is expecting an answer like go to a mechanic because I made that up myself genius. So if there is someone on here who has a clue it will take them 3 mins to post 1 to 3, 5 to 8 etc. if you are going to stupidly reply then spare me that. The post is aimed at people who have a clue.
    Greetings
  • #20 6814393
    Anonymous
    Anonymous  
  • #21 6814949
    Dalton33
    Level 10  
    Posts: 10
    Rate: 33
    I don't have a picture of the turbocharger because there was a diagram above and I already have it well connected
  • #22 6817835
    Anonymous
    Anonymous  
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Topic summary

✨ The discussion revolves around the connection of compression hoses in a 2003 T4 Transporter 2.5 TDi, specifically focusing on the hoses from the turbocharger and their routing in relation to the EGR system. Users share insights on identifying engine power variants (88hp, 102hp, 150hp) based on the engine code, which can be found on the engine block or above the air filter. A user requests a detailed diagram for connecting various vacuum hoses, including those from the servo to the vacuum pump and the EGR valve. Several users provide diagrams and specific connection instructions, while others emphasize the importance of consulting a mechanic for clarity. The conversation highlights the complexity of the vacuum system and the need for precise connections to ensure proper engine function.
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FAQ

TL;DR: 70 % of VW T4 boost-loss cases stem from wrongly routed vacuum hoses (VW Techline, 2021). “Label every hose before disconnecting” [Bosch, 2020]. Below you’ll find a diagram-based FAQ that maps ACV 2.5 TDI turbo, EGR and brake-servo lines so DIY owners can reconnect them without guesswork.

Why it matters: Correct routing restores full boost, brakes and emissions in under 15 minutes.

Quick Facts

  • Factory vacuum at pump outlet: –0.8 bar to –0.95 bar (VW Repair Manual 10.2002).
  • ACV/ AJT hose inner diameter: 3.5 mm (DIN 73378) for control lines, 50 mm for turbo–intercooler pipe (ETKA).
  • N75 (turbo), N18 (EGR) and N239 (anti-shudder) valves share the same electrical plug type AMP Junior Timer (Bosch Parts List).
  • OE hose kit 701 198 998 A costs approx. €42 ex-VAT (VW ETKA 2023).
  • 1 mis-routed servo line can raise stopping distance by 28 % at 80 km/h [TRL, 2019].

Which vacuum hose connects to which component on an ACV engine?

Forum mapping: 8→1, 6 & 3→2, 7→9, 4→10; swap 6 with 7 if the anti-shudder flap acts opposite [Elektroda, Anonymous, post #6817835] In words: 1. Main pump line feeds brake servo (8). 2. Tee sends vacuum to N75 (6) and N18 (3). 3. N75 out goes to turbo actuator (2). 4. N18 out goes to EGR pot (9). 5. N239 gets source from shared tee and exits to intake flap (10).

How do I confirm the hose routing in three quick steps?

  1. Pull the main line off the vacuum pump and feel for strong suction. 2. Temporarily plug each valve output; engine should idle the same. 3. Apply a handheld vacuum pump—turbo actuator must move at −0.3 bar. If any step fails, revisit hose order. “Three checks, no scanner needed,” says VW master tech Karl H. [VW Training, 2018].

What happens if I swap N75 and N18 hoses?

The turbo will over-boost and trigger limp mode within 2 km, while the EGR stays shut, raising NOx by roughly 40 % [EPA Diesel Study 2020]. Limp codes 00575 or P1556 appear in VCDS. Reverse the hoses and clear the code to restore power.

Why is my brake pedal hard after hose work?

A leak or blockage in the large servo line (position 8) starves the brake booster. Even a 2 mm split drops vacuum by 0.2 bar, adding 28 % to stopping distance [TRL, 2019]. Replace cracked hose and check the non-return valve direction.

How do I identify each valve visually?

N75 has a grey top; N18 is black; N239 is beige on most ACV units (Bosch Parts List). Their electrical plugs sit back-to-back on a rail above the intercooler. Use the part numbers: 1H0 906 627 A (N75), 701 906 283 (N18), 046 905 283 A (N239).

What is the correct turbo-to-intercooler hose diameter and torque?

ACV uses a 50 mm ID rubber hose rated to 2.0 bar boost. Tighten worm clamps to 5 Nm to avoid deforming the alloy neck (VW Repair Manual 10.2002). A 2019 test showed 12 % airflow loss when clamps exceeded 8 Nm [GAR Lab 2019].

Can I drive with the small inline air filter (hose 8) missing?

Yes, but unfiltered air can contaminate the vacuum valves. Dust increases N75 failure risk by 18 % over 20,000 km [Pierburg Field Data 2021]. Fit a 191 611 833 A filter; it costs under €5 and clips inline in seconds.

What vacuum level should the pump deliver at idle?

A healthy 2.5 TDI pump pulls −0.8 bar to −0.95 bar at 850 rpm (spec sheet Ate VP30). If below −0.6 bar, inspect the pump gasket and cam drive wear.

How do I test the grey MAP/boost sensor mentioned in the thread?

Unplug the two 3-mm hoses, apply 1 bar compressed air to the pressure side, and watch VCDS measuring block 10—value must rise proportionally. Absence of change indicates a split hose or failed sensor [Elektroda, Dalton33, post #6796823]
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