For those of you helping me with my half-throttle boost surging issues, here is a VAG-COM graph...
05-26-2005, 09:14 PM
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For those of you helping me with my half-throttle boost surging issues, here is a VAG-COM graph...
<center><img src="http://www.personal.psu.edu/users/b/n/bnl107/Block%20115.gif"></center><p>
I made this this evening. I ran from a dead stop at 1/2 throttle (1st and 2nd gear). As you can see, the boost builds before it is requested, then drops when it is requested, and then builds again. What do you think?
I made this this evening. I ran from a dead stop at 1/2 throttle (1st and 2nd gear). As you can see, the boost builds before it is requested, then drops when it is requested, and then builds again. What do you think?
05-27-2005, 05:22 AM
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There is a small pin-hole on the bolt part of the "to wastegate" output part, which...
the instructions said should not be moved, or else the MBC would not function properly (I didn't move it). I'm not sure if that is a bleed hole or not though. What are your thoughts?
05-27-2005, 05:31 AM
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Pretty much all MBCs have a bleed hole if they are designed to function in MBC-only
configurations. I was asking if you had plugged the bleed hole on yours, so I guess thats a no.
With the bleed hole open, the MBC controls spoolup and initial boost. Likely what is happening is the MBC is causing boost to spool faster and higher at part throttle than the ECU wants. The ECU then sees this and adjusts accordingly (dumps boost, cuts throttle, or something).
Did you have the problem before installing the MBC? I think you need to plug that bleedhole, but to confirm, try running w/o the MBC (i.e., N75 only) and see if the issue goes away.
-Dave Pramanik
With the bleed hole open, the MBC controls spoolup and initial boost. Likely what is happening is the MBC is causing boost to spool faster and higher at part throttle than the ECU wants. The ECU then sees this and adjusts accordingly (dumps boost, cuts throttle, or something).
Did you have the problem before installing the MBC? I think you need to plug that bleedhole, but to confirm, try running w/o the MBC (i.e., N75 only) and see if the issue goes away.
-Dave Pramanik
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05-27-2005, 05:39 AM
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Does that hole on the output stock sound like a bleed hole then? (more...)
If so, what would be a good way to plug it? Would a dab of good epoxy glue do the trick? Is there a way to plug it that isn't permanent?
As I had said before, the problem might have started with the MBC, I'm not really sure. Sounds like that probably is the problem though. Thanks for the info.
As I had said before, the problem might have started with the MBC, I'm not really sure. Sounds like that probably is the problem though. Thanks for the info.
05-27-2005, 05:48 AM
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Yes, that's definitely the bleedhole...
The MBC only has two connections, unlike the N75. So without the bleed hole, any pressure that it sent to the wastegate line would remain in the line and hold the wastegate open even after boost pressure dropped below the MBC setpoint. The bleedhole serves to vent the pressure in that line so the wastegate can close.
Depending on the size of the hole, you could JB Weld or epoxy a nail or screw into the hole. That way if you wanted remove it at some point in the future, you could easily do so.
-Dave Pramanik
Depending on the size of the hole, you could JB Weld or epoxy a nail or screw into the hole. That way if you wanted remove it at some point in the future, you could easily do so.
-Dave Pramanik
05-27-2005, 05:55 AM
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If the MBC body is just a plain brass T fitting, buy another T fitting and swap the guts over.
It's the cheapest non-permanent but permanent way I could think of 
Worked perfectly too, go figure.
Worked perfectly too, go figure.