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Old 05-04-2012, 09:17 PM   #1
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Default Dear sirs,

I HAVE AN OFFER OF EMPLOYMENT FOR YOU, AT THE SUM OF TEN THOUSAND ($10,000) PER WEEK. THIS...

Wait, I mean. I'm having a problem with entering boost at full throttle.

I'm ------- fine at low to mid throttle. Boost is great, everything works as anticipated. But full throttle, it's like all the power suddenly cuts out for a second, then it kicks in again.

My hunch is that it is the BOV. My BOV does not open when I would expect it to, and my hunch is that when it sees sufficient boost, it is then forced open regardless.

Enclosed are two datalogs of this happening. Advice would be appreciated.
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File Type: msl 2012-05-04_16.46.23.msl (181.8 KB, 153 views)
File Type: msl 2012-05-04_16.47.45.msl (206.7 KB, 79 views)
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Old 05-04-2012, 10:50 PM   #2
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the blow off valve when in boost should have equal pressure either side of the diaphram but has the spring as a helper to keep it shut.
so I doubt its getting forced open.

looks like some sort of fuel cut from the log and my limited experience of reading logs.

notice the duty cycle goes strait to 0 at first part of the problem then your boost drops after the fact and you go pretty lean.

I doubt its spark related as it would look far less violent.

so go through ms and check if there are any fuel cuts going on.
im almost positive your overboost protection is set to 167kpa and you hit fuel cut.
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Old 05-04-2012, 11:17 PM   #3
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Holy ----, you are amazing. Yes, that's exactly what it is - it somehow got reverted to old settings!

Awesomesauce, thanks man!
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Old 05-04-2012, 11:28 PM   #4
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you're welcome mate.

sometimes it just takes an extra set of eyes to see.
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Old 05-04-2012, 11:42 PM   #5
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Yeah, it's totally obvious in hindsight, but I totally missed that.

Thanks again!
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Old 05-05-2012, 06:45 PM   #6
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btw BTW BTW BTW

For future tuning notes for other people too---

Your EMS and it's MAP sensor is of course, MUCH more sensitive than a typical analog boost gauge. It is common to have significant spikes up to 5+psi that last a fraction of a second etc that you will not see on a needle.

Assuming you are not going lean and your motor can handle it, this is not a big deal.

When tuning boost though, I have often run into this issue, and had to set my overboost protection much higher than the "steady state" level of boost.

A restriction in the boost controller signal line, either be it a MBC or EBC solenoid will cause spikes. It will also cause faster boost rise. Trade offs. If you have spikes with your MBC you can drill out the hole on the signal side of the MBC.

For small GT25 turbos, this is not really an issue. The turbo spools so quickly that you don't need to spend much time optimizing spool. For big turbos though, shifting that power curve to the left as much as possible is a very worthwhile pursuit.
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Old 05-05-2012, 06:45 PM   #7
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Super btw, I am not drinking today.
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Old 05-05-2012, 08:44 PM   #8
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So, update.

Went in underneath the car, and ended up taking the eBay BOV apart. Why?

It was missing the ------- adjustment screw. So yeah, there was also a big BOV leak mixed in there.

Basically rebuilt the damn BOV, and it works a lot better now too.
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