Do I have a faulty MBC? Symptoms ->
05-18-2004, 06:56 AM
#1
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Do I have a faulty MBC? Symptoms ->
When I pressure tested my charge system, I heard only a hissing that I identified to be air escaping at the drilled vent hole in my JoeP MBC. Had no other leaks. My logic is: the system was only pressurized to about 5-10 psi (couldn't tell exactly from the compressor gauge), so the ball and spring should have been holding the air back from reaching the wastegate side of the MBC (it's set to 15psi). The pressure wasn't reaching the wastegate side from the other direction either, so why would air be escaping from the bleed hole? My only answer would have been that there is a leak or something internal to the MBC. Other than this it seems to work pretty well. The only other symptom is a slight reduction in boost as rpms increase (decreases maybe 1-2 psi max). What do you think? Any other explanations?
05-18-2004, 07:10 AM
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Ok, I know what the hole does. Yes, it's useful, explanation:
The hole (for those that don't know) just bleeds pressure from the wastegate line after you let off boost so that the wastegate can shut quickly.
Since it's on the side of the MBC that goes to the wastegate, it shouldn't see ANY pressure until the other side of the MBC hits MORE than the preset pressure - 15 psi in this case.
Since it's on the side of the MBC that goes to the wastegate, it shouldn't see ANY pressure until the other side of the MBC hits MORE than the preset pressure - 15 psi in this case.
05-18-2004, 07:12 AM
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It's not. I'm positive. After all, if that were the case I'd basically be running with
wastegate shut ALL the time, and I should get boost creep, but I don't. I can actually control boost with my MBC as is, and it goes no higher than 15 psi right now.
05-18-2004, 07:57 AM
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No it would not be running shut, you have the version with ball bearings on each side of a spring...
correct? It is possible to reverse the MBC. The purpose of the hole is to bleed off any residual pressure when MBC is closed and eliminate creep.
It only take 5 psi or so to open the actuator with no boost control at all.
As far as your leakage, hmm thats a tough one if the MBC is installed correctly, must be getting some bypass somewhere.
It only take 5 psi or so to open the actuator with no boost control at all.
As far as your leakage, hmm thats a tough one if the MBC is installed correctly, must be getting some bypass somewhere.
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05-18-2004, 08:40 AM
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if the MBC were reversed, it would take more than the desired pressure to open the wastegates
because the bleed hole would bleed off some of the pressure before finally passing through the MBC...right?
