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Old 10-04-2013, 08:29 AM   #1
lilfleck
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Boost Fluctuation @ WOT -- Bad DV?

Hey guys,

I noticed that the boost needle fluctuates up and down at WOT sometimes. I have a Rev C DV. When I installed it during the K04 install, I checked it and it looked fine; no tears.

I tightened the crap out of the turbo outlet pipe clamps and ensured the (green) O ring gasket was on the intercooler piping.

Could a leak on the intake cause this?
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Old 10-04-2013, 08:34 AM   #2
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Depends on what REV C you have. Newer REV Cs are actually piston type valves like the REV D but make less noise.

What sort of range is the fluctuation? Like a spike around 24 down to 20 and hold at 21-22?
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Old 10-04-2013, 09:18 AM   #3
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How do I know if its pistol vs a diaphragm style?

I spike at 23lbs and it usually holds at 19lbs. Sometimes the needle jumps up and down to what looks like 23-21-19-21-19-21-19. I think I have to adjust the needle on the boost gauge because when the car is off it doesn't rest in the exact center of 0. It rests a little bit to the left. That being said, if it is off, it could be slightly higher.

It's not easy running logs by myself. Trying to find a good stretch of road that I can run on is tough and it has to be really late at night for no cars to be around. I tried running one log on the highway after I replaced the elbow. I did hit some bumps in the road, but here are the timing vs boost requested vs actual:

0 300 1040
1.53 570 1030
3.31 1740 1100
3.31 2400 1330
4.08 2400 1720
6.38 2390 2340
6.38 2390 2280
6.63 2390 2330
6.88 2400 2310
6.88 2400 2300
6.63 2380 2290
6.38 2310 2200
6.12 2260 2110
5.61 2140 2040

Also worth noting that I recorded misfires on 3/4 cylinders during this log. I have new coil packs and plugs on standby...

Last edited by lilfleck; 10-04-2013 at 09:24 AM.
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Old 10-04-2013, 09:05 PM   #4
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It has nothing to do with your dv, if your gauge is jumping around like that on throttle then it's compressor surge. Your turbo is working out of its efficiency range at those engine speeds and making more boost than your engine can swallow. This results in a reversal of air flow through the compressor which will make it 'chop' air instead of push it; it's an issue with your tune.
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Old 10-04-2013, 10:29 PM   #5
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Go log rpm, n75, requested, and actual. See what the n75 is doing if its pegging during the fluctuations you have a leak somewhere.
Also before you log check the ambient pressure so you can subtract it from the boost values to get actual gauge pressure.
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Old 10-09-2013, 07:16 PM   #6
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Old 10-09-2013, 08:59 PM   #7
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Quote:
Originally Posted by apa11393 View Post
It has nothing to do with your dv, if your gauge is jumping around like that on throttle then it's compressor surge. Your turbo is working out of its efficiency range at those engine speeds and making more boost than your engine can swallow. This results in a reversal of air flow through the compressor which will make it 'chop' air instead of push it; it's an issue with your tune.
This

That is a documented issue with APR ko4 isn't it?
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Old 10-10-2013, 10:00 AM   #8
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since the weather got cooler here in texas, i started noticing slight rpm fluctuations as well when im going wot. i have a digital boost gauge too and boost seems to fluctuate also. inputs?
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Old 10-10-2013, 10:48 AM   #9
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great write up
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Old 10-10-2013, 11:13 AM   #10
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On my to do list... once I isolate the leak, I will look into it. I don't want to add any additional variables to the problem before resolving it.
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Old 10-10-2013, 12:59 PM   #11
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Mine fluctuates and I'm stock have the new south performance boost gauge
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Old 10-10-2013, 04:30 PM   #12
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Quote:
Originally Posted by GreasyGinzo View Post
This

That is a documented issue with APR ko4 isn't it?
Yes it is
Quote:
Originally Posted by Sleepin gti View Post
Mine fluctuates and I'm stock have the new south performance boost gauge
How so?
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Old 10-10-2013, 06:45 PM   #13
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According to that small amount of data, there is absolutely nothing wrong.

Granted it isn't perfect, but it's not a serious issue. Could be a small leak or could just be nothing. Because it is such a relatively small problem, finding it will be difficult and hard to quantify in data.
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