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    Thread: Over boosting with unofficial tune

    1. Semi-n00b
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      08-22-2020 10:30 AM #1
      A friend of mine works closely with a tune shop to help me backyard tune my mk4 1.8t wagon. We use nefmoto and all that stuff to achieve this. We adjust fuel, timing, n75 duty cycles, and few other parameters and constantly adjust and fiddle with them to get the right spot for power and boost.

      I’ve noticed during all of this that I have ridiculous amounts of boost fluctuations, boost waves as I call them. I have my k03 (k03s?) tunes at 15psi and under WOT, I get those waves where my boost goes from 12 to 15 and does that until I let off the throttle.

      What causes this? I’ve checked all boost hoses from the turbo, to the n75, all the TIP lines and I’ve replaced as many clamps as I could. I’m still getting this issue and neither my friend or I can figure out what’s going on.


      2004 VW Jetta GLS “Estate” Wagon - 1.8T -O2J

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    3. Member Brake Weight's Avatar
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      08-22-2020 11:55 AM #2
      Are you using an MBC?
      Quote Originally Posted by Anony00GT View Post
      Who's the idiot that deleted the EVAP solenoid?

    4. Semi-n00b
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      08-22-2020 11:58 AM #3
      Quote Originally Posted by Brake Weight View Post
      Are you using an MBC?
      Believe so. He does the tuning bit. I’ll ask him.


      2004 VW Jetta GLS “Estate” Wagon - 1.8T -O2J

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    6. Semi-n00b
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      09-16-2020 08:04 PM #4
      Quote Originally Posted by Brake Weight View Post
      Are you using an MBC?
      I have no idea why it took me so long to figure out what that meant.

      No, I’m not using an MBC. Stock k03 (k03s?) turbo. Used the same tuning on a Wolfsburg with a confirmed k03s and had the same issues. Tried swapping out the n75 and that changed nothing. Again, boost hoses are air-tight and overall look fine. Limp mode happens more often than not and I can’t really understand why, but it could be from boosting right to 15psi and then boost just pulses from 13-15 under WOT


      Sent from my iPhone using Tapatalk

    7. Member Brake Weight's Avatar
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      09-16-2020 08:45 PM #5
      So two separate vehicles with similar tune and both did the same thing with boost fluctuations? Sounds like the tune to me.

      Can you flip the DV opposite of how it is now? It’ll still work but there is more surface area for air pushing against the piston. Where is the feed for the DV coming from? Is the n75 plumbed correctly? Have you seen the ‘spring mod’ for the wastegate actuator? That could help some.
      Quote Originally Posted by Anony00GT View Post
      Who's the idiot that deleted the EVAP solenoid?

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