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I just recently did the bleeder T mod on mkiv.com, except instead of using a 1/4" bleeder T (which gives 15psi boost), I finally ended up settling on a brass adjustable air pressure regulator to have adjustable boost. Currently, the boost is set to about 13psi so I don't hit fuel cut at 14psi. However, I noticed a problem when I performed this mod, regardless of whether it's with the bleeder T or with the adjustable air pressure regulator. The problem is that the boost is unstable. It doesn't hold at what it's set to, regardless of whether I use a bleeder T or the adjustable air pressure regulator. Either way, boost doesn't stay stable at what it's set to, and it's very frustrating . For example, right now, I've got boost set to 13psi with the adjustable air pressure regulator, and when I floor it on the freeway in 2nd gear, the boost first goes to 14psi, then quickly drops to 13psi, then holds at 13psi for a little, then as rpm steadily increases it drops to 12psi, and then drops to 11psi by 6,000+rpm all the way to redline. Then when it shifts to 3rd gear, it jumps to 14psi, then quickly drops to 13psi and either holds at 13psi till redline or goes down to 12psi or 11psi as the rpm increases toward the redline. Generally, the higher the rpm and the closer to redline, the less the boost, although on and off it will hold 13psi all the way till redline, it just depends on the gear and the "mood" of the car. Higher gears its more likely to hold at 13psi, or at least 12psi. 1st and 2nd gear for example go to around 12psi overall, and sometimes to 11psi. WTF IS GOING ON?!?!? 11psi! I WANT 13PSI THROUGHOUT THE ENTIRE REV RANGE ALL THE WAY TO REDLINE IN EVERY GEAR, not 12psi at higher rpm's and then 11psi at 6000+rpm till redline, wtf! 11psi is basically stock boost! Does any one know what's causing this problem with unstable boost? Higher gears seem to get more boost than lower gears, and the boost seems to have a mind of its own of where it wants to go between 11psi-13psi. I have some reasonable suspicions at what the problem may be, but I wanted to get some input first. Does anyone have STABLE boost on the stock turbos with no fluctuations from what you've set the boost to? If so, what boost control device are you using?
 

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(overspooled)
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Josh S said:
the bleeder t/ your air pressure reg. are poor ways to increase boost and don't work well. Get a quality MBC or EBC and that will help a lot toward stable boost control.
:bigthumb:

...And good luck maintaining such low boost, you'll likely see spikes, and...get a BCC
 

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WI-FI FTW, GTFO fuse box!
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8,108 Posts
w/g spring mod?
the reason it is getting higher boost in the +rpm range is because the intercooler is more efficient and condensing the air more
-jt
 
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