Mk5 gti with low boost issue

Discussion in 'Mk5' started by Eliters, Jun 10, 2019.

  1. Eliters New Member

    Joined:
    Jun 10, 2019
    Likes Received:
    0
    hi all, hoping someone can shed some light on this.

    Got the car last week with a boost shown on gauge of 0.5 bar max, usually 0.3.

    Car drives fine apart from the obvious lack of power.

    So far, it’s had a new maf, diverter valve which is the new type with o ring as opposed to the diaphragm version, I’ve cleaned the maf again anyway and also the map sensor, checked and cleaned all earths under the battery tray, measured fuel pressure on boost which is 1500psi+ and atmospheric pressure reads at 14.5 bar so is about right and there are no lights on.

    I unplugged the maf but it made no difference. Weirdly, it didn’t show a warning light either though which I thought odd, but is measuring airflow ok. At 0.4 bar it’s showing about 110 g/s. At full boost I know it should show 190-210 so at the lower boost, I’d imagine this to be about right.

    Unfortunately I no longer have a windows laptop so cannot log requested boost. I have an app but it’s showing calculated boost at 75psi so I’m guessing this car doesn’t show boost in a digital way very well with most apps.

    I’m tempted to try a map sensor as when the car reaches 0.5 bar and the revs climb a bit, you hear the dv open slightly and the gauge drops a bit then it closes and it climbs back etc. This cycles until you change gear or keep the revs up which in turn makes the boost drop to around 0.2.

    I’m guessing that it’s more or less running on actuator boost and the n75 isn’t commanding any boost, that or the new diverter was fitted wrongly by the previous owner. Not sure that’s possible though? Also blown through the pcv and it’s nit possible so that’s ok.

    So, any other fresh ideas anyone?

    To sum up,

    Common parts replaced as above, common failings addressed, no eml, drives fine and has fuel pressure, just next to no boost!
     
  2. GVK

    GVK Forum Addict

    Joined:
    Oct 23, 2003
    Likes Received:
    426
    Location:
    Lincs.
    wastegate actuator could be weak.

    Have you had a smoke test to check for leaks?

    Flat out you should see 160 g/s for a 200hp engine.
     
    Last edited: Jun 10, 2019
  3. Eliters New Member

    Joined:
    Jun 10, 2019
    Likes Received:
    0
    Perfect, thanks for the reply.

    I haven’t smoke tested so far. I’ve visually checked all hoses and the only one that shows even a slight misting of oil is the hot side pipe where metal meets rubber at the front. It doesn’t sound like a leak though when out on the road.

    It has a ramair stage 2 induction kit fitted so you get a hiss when on boost through the filter, but also get a slightly different pitch of hiss on lift off, so I think what I’m hearing is the turbo spooling and sucking air.

    I’m seeing 110g/s at a push at 0.4-0.5 bar so I’d guess at full boost I should see higher as it will be pushing more air?

    Do you know if it’s possible to fit the new revision dv incorrectly? If so, I’ll pull it and double check as I didn’t fit it although I can see it’s new.

    It just feels like it’s not asking for boost and relying mainly on the actuators pre-load. But without logging I know it’s impossible to check.

    Although there are no lights on (it comes on and goes off on start) when I scan with a paid app, it shows me 4 p codes but these do not show up on any obd scan so I’m guessing they must be manufacturer specific?
    I know p codes are powertrain so are to do with this issue no doubt, but without the proper software I can’t read them. Just find it odd that it doesn’t show any lights for these or when the maf is unplugged.
     
  4. GVK

    GVK Forum Addict

    Joined:
    Oct 23, 2003
    Likes Received:
    426
    Location:
    Lincs.
    My hotside pipe mists oil in the same place too.

    110 g/s would be about 137hp, think from memory you should see at least 0.7 bar maybe with a 0.9 spike on initial accel.

    Not had much to do with the DVs, slight chance could get the diagphragm trapped when fitting as they aren't in the easiest place to fit on the K03s

    I use OBDeleven app on mine, you can get it from ebay for £60 or so, it gives full VAG codes and diag. Much cheaper than VCDS. Think they support IOS now too.

    Some P codes will still be present but show no MIL, things like the P0441 purge valve flow code that every mk5 seems to have.

    Really need to know what those other codes are before you start throwing the parts cannon at it.

    What area are you from, you may have someone local with VCDS or something that can be used for logging?
     
    Last edited: Jun 10, 2019
  5. Eliters New Member

    Joined:
    Jun 10, 2019
    Likes Received:
    0
    Ahh ok, it didn’t look terminal I must admit so doubt it could lose that much through that.

    That seems to coincide with what I’ve read online and videos I’ve watched. They seem to spike to around 15 psi and settle at around 11 so I think that is about right. I get a spike to 0.6 if I’m really lucky and go from no throttle to full, otherwise if I feed the throttle in I get 0.3 religiously.

    Think I may pull the dv then just to rule it out. It does look and intense pain to get to though, even with the wheel off and liner out!

    I’ll have a look into that, thanks.
    I had vcds but now have a MacBook and there’s no support for Mac sadly.

    It feels like it’s not requesting boost on the drive to be honest, feels ok when accelerating but unless you get the throttle right it’s reluctant to boost above 0.3.

    It’s supposed to be mapped too as the previous owner, like some people do, thought that would solve it! Needless to say it didn’t!

    Cant wait to get it right, just seems to be challenging me hah!
     
  6. GVK

    GVK Forum Addict

    Joined:
    Oct 23, 2003
    Likes Received:
    426
    Location:
    Lincs.
    Last edited: Jun 10, 2019
  7. Eliters New Member

    Joined:
    Jun 10, 2019
    Likes Received:
    0
    That fits in with the 190-210 that I originally thought I should be seeing then.

    Originally I was looking towards n75 or map sensor. I did all the earths tonight hoping it would help but no joy so back to the drawing board!

    As you say, those codes would probably at least point me in the right direction. I did 14 years as a diagnostic tech so have no issue with understanding how things work and what I should roughly be seeing etc, just annoying not being able to test each sensor and having a heads up from the codes.

    I’m based in Sussex I’d theres anyone local who had vcds and a laptop :)
     
  8. GVK

    GVK Forum Addict

    Joined:
    Oct 23, 2003
    Likes Received:
    426
    Location:
    Lincs.
  9. Eliters New Member

    Joined:
    Jun 10, 2019
    Likes Received:
    0
    Perfect, thanks. I did sign up to there, but when I tried to post in the new users thread to say hi, there was no “new thread” button so I gave up haha
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice