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Old 12-22-2014, 06:01 PM   #1
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Default Oscillating boost when reaching boost target

I don't know if this is normal but I have my target boost set up at around 8-9psi using a MBC and 5.8psi EWG spring. You can see on my log that boost initially oscillates and spikes more than I would like it to. On this log it went up to 168kpa and then it tappers to 150-155 kpa. Ultimately my goal is to run 180kpa across the board but I am afraid that when I start reaching target boost the wastegate spring will oscillate and boost will spike to 190-200kpa.

What can be done for boost to be more gradual without going up and down? Maybe this is normal...

The red line on the top graph is KPA, white is RPM
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Old 12-22-2014, 06:19 PM   #2
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I've had this happen on a friends msm. Is the oscillation visible on the boost gauge?
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Old 12-22-2014, 06:53 PM   #3
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I've had this happen on a friends msm. Is the oscillation visible on the boost gauge?
I haven't actually looked at the boost gauge, but I don't think it moves around, its an old jackson racing gauge and I wonder if its even accurate, I just go by the logs. The MS vacuum source is to the back of the intake manifold. I have the wastegate source coming from the intercooler outlet about 4 inches from the throttle body.
The MBC is a cheap NSX one, I took it apart and I have my doubts about the cheap looking spring in it.
I am trying to decide if I should buy another MBC (High Perfomance Boost Controller - TurboXS)
or install a 11.6psi Tial spring and be done with it
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Old 12-22-2014, 08:23 PM   #4
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where's the boost source EXACTLY?
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Old 12-22-2014, 09:34 PM   #5
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The ms source is next to the fpr on the original fpr source nipple.
The boost source is on the end tank of the intercooler. I have a water to air cooler so that makes the end of the intercooler about 4 inches from the throttle body

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Old 12-23-2014, 08:12 AM   #6
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looking again, it's not just your boost signal that's noisey fwiw.
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Old 12-23-2014, 09:38 AM   #7
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looking again, it's not just your boost signal that's noisey fwiw.
What do you sugest I do? The wide band is grounded to te back of the head by itself to one of the holes were the coil pack was bolted to before having cops. Before that I was grounded to the ground by the fpr. The ms vacuum surce it's on the recomended location.
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Old 12-23-2014, 09:47 AM   #8
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yeah actually, your o2 is pretty stable. your MAT and CLT is also stable, so looks like the spark and fuel is reacting to the MAP Signal.

typically the fpr source is a very clean signal. Id suggest trying a little fuel filter on the line to dampen it.
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Old 12-23-2014, 10:11 AM   #9
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do you have the higher wg spring? I'd eliminate the variables by taking the mbc out of the equation
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Old 12-23-2014, 11:30 AM   #10
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Default no mbc

Here is a log with he 5.8psi spring and no MBC.
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Oscillating boost when reaching boost target-ewg-5.8psi-spring.png  
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Old 12-29-2014, 08:36 PM   #11
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Thanks to Braineack, I added an inline fuel filter to my MAP vacuum source to the MS, the graph looks much much better.
Also, I want to add...I'm proud of my stock 1.6L and journal bearing T25 making 8psi at 2960rpms!
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Old 12-30-2014, 08:59 AM   #12
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yeah that looks typical now.
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