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Boost gauge going off the scale??

Discussion in 'A4/S4 forum(B5 Chassis)' started by Soupie69uk, Oct 6, 2007.

  1. Soupie69uk
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    Soupie69uk Owner

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    [Oct 6, 2007]
    Any ideas guys, was driving along the bypass tonight at about 70mph and was going to speed up a little.

    So accelerated a tiny bit and the car was almost jerky hardly noticable though. Then I pressed my foot down a bit more and the boost gauge flew round to 25+psi so I removed my foot and the car like stuttered. Similar to if someone bangs a clutch.

    Also another little not so important question. What does stiffening the spring in my DV do? Just last week I tightened it up a bit to stop it blowing off so easily.

    Cheers.
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  3. satans child
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    satans child project...satans child

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    [Oct 6, 2007]
    hi soup...
    1st of all im asuming you have an adjustable forge dv yes.????
    if so you have wound it up too much which is why your turbo is about to go BANG !!! if your running 25 psi

    back it off quick

    if its not blowing off your not acheiving the boost levels your dv spring now needs to let go of the pressure..
    but too much boost will kill your ko3 in no time at all

    hope this helps bud...:icon_thumright:
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  4. Jimbo.King
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    Jimbo.King Active Member

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    [Oct 7, 2007]
    I wouldnÂ’t have thought the dv would make any difference on the boost pressure the n75 valve electronically controls the pressure.

    You could have a faulty actuator / split pipe to actuator from n75 valve,
    (this will not allow the actuator to open the wastegate, causing the overboost)

    N75 valve Fault (sticking inside)

    What boost pressure are you running the k04 at usually.

    I assume you have put a different colour spring or shimmed it with a thicker washer to stiffen the dv up,
    all this will do is if you are running high boost it has a better clamping load to maintain boost pressure more reliably to prevent leaks,
    if you go too much it wont dump at all causing damage as the air rushes back into the turbo trying to stall/slow it down.

    Might be worth running vagcom to see if anything has come up.
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  5. Soupie69uk
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    Soupie69uk Owner

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    [Oct 7, 2007]
    Thanks for the replys guys.

    I have a GFB valve which you can tighten the spring on the top just by tightening in up. It diverts the air and can blow some off. I have run this for around 40k miles.

    I did this as it was activating far to easily. You think I have maybe over done it? It has been fine all week until now.

    Cheers.
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  6. Markey
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    Markey Active Member

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    [Oct 7, 2007]
    If your actuator was faulty then you could over boost a little but you have had the K04 so it would have a new one fitted so i would rule this out for the moment.
    It could be a faulty N75 if you have vagcom you can check it you can hear it open and close. When i had the N75j it was over boosting badly and then the car kept hitting limp mode.
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  7. Soupie69uk
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    Soupie69uk Owner

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    [Oct 7, 2007]
    Right guys I have been out and loosened the dv spring off a lot and it is still boosting up to 25+psi. Not sure what to do now.

    Am thinking about taking out the K04 and putting the K03s back in to see if its any better with that on. Will be such a hassle though.

    Think my clutch is slipping a bit worse now to.
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  8. Markey
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    Markey Active Member

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    [Oct 7, 2007]
    I would not go as far as to swap the turbos back, who did your map get them to have a look as it should still be warrantied.
    #7
  9. Soupie69uk
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    Soupie69uk Owner

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    [Oct 7, 2007]
    I have just got my K03s map on the car, never had any issues until now.

    Think I will need to get VAG.com to sort this out.
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  10. Markey
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    Markey Active Member

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    [Oct 7, 2007]
    Me to mate, it can't be turbo associated as you have had it on for ages now.

    If you can try swapping you N75 with a mate or somthing just to rule that out.
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  11. Soupie69uk
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    Soupie69uk Owner

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    [Oct 7, 2007]
    Few guys are thinking it could be the wastegate not opening? How could I test that?

    Yeah wish I had a spare N75 about.
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  12. Jimbo.King
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    Jimbo.King Active Member

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    [Oct 7, 2007]
    A turbo swap sounds a little drastic,
    Have you checked all the pipes going from the turbo / actuator to the N75 valve are tight on the clamps + no splits or holes
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  13. Soupie69uk
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    Soupie69uk Owner

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    [Oct 7, 2007]
    Yeah been out and had a peek at all the hoses around the turbo and on the intercooler they all seem ok. Some are hard to see.

    Think I will just have to get someone to VAG.com it and maybe I just need bite the bullet and spend a few quid and get all the bits I need for the K04. Then get it mapped by mrc so I know all is well.

    Will just be a case of checking what other bits I now need.
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  14. Markey
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    Markey Active Member

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    [Oct 7, 2007]
    Im sure mr MRC might help you out by checking it if you speak to hom about getting it mapped there.

    The waste gate is always open unless you are boosting then it closes, to reach boost by making the air pass throught the tubine rather than bypassing throught the wastegate :) it is possible that it is stuck shut maybe but then you would just boosting all the time but the N75 controlls the actuator so that would be my first thing to check as you have had the new tubbie.
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  15. jcb
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    jcb Active Member VCDS Map User

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    [Oct 8, 2007]
    lot of "odd" info on this one.

    1st - your dump valve, which I assume is a "recirc valve" doesn't control boost and can only open when you back off the throttle and dump the pressure from the inlet manifold system. If that wasn't working due to the spring in your "dump/recirc valve" you would have a more worrying compressor stall as the inlet charge came reverberating back towards the turbo when the throttle snapped shut. that will kill your turbo.
    you would see a spike but on backing off, not on accelerating and only if your gauge takes its signal from the inlet manifold before the throttle body.

    2nd - The wastegate isn't open "until boosting". it is closed and gradually opens to control the level of boost. If you are set to achive a max of 18psi it will start cracking open at a much lower level . If it didn;t or the former was true you would go from zero boost to maximum boost and back down if you alternated between throttle on of off at high revs. very jerky indeed.

    As you are running an N75 I would start here as either it or one of it's signals is likely to be the problem, check all inlet and outlet lines, check its signal line, check the wastegate actuator and signal line (skinny vac tube).
    You haven't cranked the threaded bar up on the actuator have you? (common mod to hold higher boost or to overboost, not sensible without an increase in fuelling, lean charge runs very hot and can burn your valves and pistons)

    where is the signal for the boost gauge coming from? inlet mani? tee'd into another line?

    If it has been running OK with your current map and a KO4 then the turbo is not your problem. its a boost control issue and that can only be the N75, the w/g actuator, the wastegate or the MAP.
    you could swap the N75 with a new one or a "j" or other version for quite cheap, if it doesn't work just stick it on eBay! or I will buy it from you, your only down the road!
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  16. Markey
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    Markey Active Member

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    [Oct 8, 2007]
    I knew it was one way round just could not remember if it was open or closed.
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  17. Soupie69uk
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    [Oct 8, 2007]
    Cheers for the info guys.

    The boost in not just on or off so I guess its not sticking shut then. The DV is working fine I think to as I can hear it work.

    I havent touched the actuator either, I have heard about people adjusting them.

    It is most likely to be the N75 valve, I have not touched it apart from looking at it yesterday checking the hoses. Maybe this has just come to the end of its life.

    The signal for the boost gauge is coming off the fuel pressure regulator (I think) I just followed the awe instructions.
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  18. macattax
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    macattax Member

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    [Oct 8, 2007]
    Just wondering where is the N75 valve actually located?
    Got any pics and how difficult is it to get to?
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  19. Markey
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    Markey Active Member

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    [Oct 8, 2007]
    it is located about half way down the intake hose and looks like this

    [​IMG]
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  20. Blue_Thunder
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    Blue_Thunder Active Member

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    [Oct 8, 2007]
    I'd disconnect it (unplug the electrical connection) until you figure out what's happening. This will limit your K04 to about 5psi (when the wastegate will open).

    If you're still getting the overboosting after this, it's the wastegate.
    #19
  21. Soupie69uk
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    Soupie69uk Owner

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    [Oct 8, 2007]
    Good test. I will try that.

    Thanks.
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  22. Beerzo
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    Beerzo Masa'warty 3200... Talk To Me!

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    [Oct 9, 2007]
    Soupie I am over in Greenock just west of glasgow i have a spare n75 valve and VAG-com if you want to get it checked out let me know.
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