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n75 im gonna cry

Discussion in 'A4/S4 forum(B5 Chassis)' started by mikeya4, May 8, 2009.

  1. mikeya4
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    mikeya4 Member

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    [May 8, 2009]
    I've only had my car a short time and its already doing my head in trying to get parts and sort things out, its the boost again, I know where all the vac hoses go around the n75 and i took the nasty mbc out and it will only boost to 4psi, when i put the mbc back and plumb it before the n75 it will spike to 22 then go to around 16-18psi, it will the drop to 12 then go back up to 16-18 and hold. I can't see it being a boost leak as it will hold there for as long as i need to. and me being an idiot and buying a 2.5 means i have to get the valve from audi and wait a week as its a "back order from germany". if i take the mbc out and it only boosts at 4psi its flat (obviously) or if i put the mbc it it spikes and goes up and down,

    right...rant over

    any ideas please?????
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  3. Lee Goodall
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    Lee Goodall ..got my head together!

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    [May 8, 2009]
    4 PSI would be limp mode.. Have you checked for fault codes?
    I pressume you are looking towards replacing the N75?

    Sounds like the MBC was fitted with a faulty N75.. possibly check the wiring to the valve if you've not already done so?

    Do you have a part number for the valve that you require as I might be able to help.
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  4. mikeya4
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    mikeya4 Member

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    [May 8, 2009]
    i haven't got vagcom at the mo. I've ordered a new n75 anyway, the valve on mine is 8d0 906 627b which has been superseded loads and needs to have new connectors etc. i might be able to borrow my bro's vagcom, dunno a bit stuck at the mo
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  5. Lee Goodall
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    Lee Goodall ..got my head together!

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    [May 8, 2009]
    I'd definitely try to get it plugged in before splashing out on parts to be honest mate; Could save you £££s.

    I don't have that valve.. Sorry.

    Symptoms definitely point towards the N75 though.

    Hope you get it sorted mate.
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  6. mikeya4
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    mikeya4 Member

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    [May 8, 2009]
    I just popped over and vagcom'd it, it came up with manifold pressure not achieved? and thats it, i've managed to figure the mbc out and got it down to boosting and holding around 13 psi, is this about right or do i need more/less? its for a 2.5 tdi so not sure what it should be boosting at,
    thanks for your help
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  7. Lee Goodall
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    Lee Goodall ..got my head together!

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    [May 8, 2009]
    What's the engine code mate?
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  8. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [May 8, 2009]
    throw the MBC in the bin, and concentrate on getting the N75 working properly

    It has three legs, one goes to the actuator, one to atmosphere and the other to boost pressure.

    Get some photos of the engine/turbo layout and post them up.
    #7
  9. mikeya4
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    mikeya4 Member

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    [May 8, 2009]
    engine code is afb. I got the hoses on the right way but it will only boost to 4 psi without the mbc, i've ordered a n75 and the fault code i believe is due to the fact when i disconnected the mbc it won't go past 4 psi which is why its limit is not reached? so basically im guessing the n75 is fooked which is why i've ordered one, but i would like to know what this car should be boosting at? any ideas


    00575 - Intake Manifold Pressure: Control Limit Not Reached
    Possible Symptoms
    Sudden complete loss of Power
    Reduced Power
    Possible Causes
    Hoses incorrect connected, disconnected, blocked or leaking
    Pressure Unit for Turbo Charger defective
    Solenoid Valve for Boost Pressure Control (N75) defective
    Possible Solutions
    Check Hoses
    Check Pressure Unit for Turbo Charger
    Check Solenoid Valve for Boost Pressure Control (N75)
    Check Basic Setting > MVB 011

    cheers
    #8
  10. mikeya4
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    mikeya4 Member

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    [May 8, 2009]
    engine code is afb. I got the hoses on the right way but it will only boost to 4 psi without the mbc, i've ordered a n75 and the fault code i believe is due to the fact when i disconnected the mbc it won't go past 4 psi which is why its limit is not reached? so basically im guessing the n75 is fooked which is why i've ordered one, but i would like to know what this car should be boosting at? any ideas


    00575 - Intake Manifold Pressure: Control Limit Not Reached
    Possible Symptoms
    Sudden complete loss of Power
    Reduced Power
    Possible Causes
    Hoses incorrect connected, disconnected, blocked or leaking
    Pressure Unit for Turbo Charger defective
    Solenoid Valve for Boost Pressure Control (N75) defective
    Possible Solutions
    Check Hoses
    Check Pressure Unit for Turbo Charger
    Check Solenoid Valve for Boost Pressure Control (N75)
    Check Basic Setting > MVB 011

    cheers
    #9
  11. Lee Goodall
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    Lee Goodall ..got my head together!

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    [May 8, 2009]
    You need to clear the codes and run without the MBC to see if that throws anything up. If there's no code for the N75 valve then there could be other issues causing lack of manifold pressure.. maybe the old owner fitted the MBC to compensate for this?!
    #10
  12. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [May 8, 2009]
    [​IMG]

    Theres the diagram i found online and modified a bit. You'll need to carefully trace all the pipes and ensure they go to the correct points on the N75.

    Green pipe will probably attach to the turbo outlet pipe.
    Blue will attach to the wastegate actuator
    Purple will attach to the air inlet pipework somewhere.
    #11

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