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Old 04-17-2004, 04:41 PM   #1
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Something weird is happening (MBC)

ok MBC is set for about 15PSI, but today in 3rd and WOT i was only about 11, in 2en i was still hitting `15no problem, anyideas?
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Old 04-17-2004, 05:06 PM   #2
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Its getting hotter out, The ECU is probably cutting back boost.
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Old 04-17-2004, 08:20 PM   #3
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Its getting hotter out, The ECU is probably cutting back boost.
With a MBC, you bypass the stock BPC so the ECU has no control over boost. Probably the screw of the MBC has gotten loose.
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Old 04-17-2004, 09:29 PM   #4
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if it was loose, why would it hold the boost in 2en but not 3rd? what if the air is just getting warmer(thicker) by 3rd or something.....
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Old 04-18-2004, 05:30 AM   #5
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No, I'm really sure the ECU still has some controll over it. Isnt a MBC just delaying the signal to the apc from the wastegate or something to that effect.

Either way, the warmer temps have alot to do with it.
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Old 04-18-2004, 07:42 AM   #6
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No, I'm really sure the ECU still has some controll over it. Isnt a MBC just delaying the signal to the apc from the wastegate or something to that effect.

Either way, the warmer temps have alot to do with it.
The ECU controls max boost through the BPC. Installed as designed, the MBC regulates pressure reaching the wastegate and bypasses the BPC altogether. The dood says he is using the MBC to set boost at 15 psi. Therefore the ECU cannot be affecting Max boost in this configuration.

You are thinking about the series installed MBC. SMBC has MBC between turbo and BPC. BPC still regulates max boost. If you are using the MBC to set max boost, it can't be in this configuration.

WIth an MBC installed to control Max boost, the only thing the ECU still controls is fueling and ignition. But dood is not triggering fuel cut out so ECU has nothing to do with it.

Here are some possiblitiies: leaky vac hoses to mbc. loose mbc screw. wastegate gone bad. wastegate actuator sticking. measuring boost in 2nd below 4000 rpm and measuring boost in 3rd above 4000 rpm (T25 sucks at flowing volume)
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