Questions about boost

[thomastollar]

Am having some issues with boost and as I track them down I have a few questions.

Boost leaks are all taken car of, check valves all replaced, and ran requested and actual boost via VCDS, which finally brought up a code for the n75 and under-boost.

This morning I unplugged the n75 to wastegate actuator hose and took the car for a just above leisurely drive. From this a few things became apparent - I am almost certain the n75 has been bad since I bought this car a year ago, because the car was boosting more consistently and for the first time I could hear the turbo clearly at around 4000rpm in 3rd and 4th (which has not happened before)...but another sound became more apparent too and this is where my real question comes in. As the car is under load in 2nd or 3rd and boosting at around 10-12 psi there is a fairly loud humming/whining (imagine a cartoon duckbill dinosaur) noise that usually lasts for one or two seconds...the Frankenturbo is less than 5000 miles, the DV is also a fairly new 710n....Any ideas?

[old guy]

If you drove with the wastegate disconnected from the N75 you should be getting well over 20 psi boost as soon as you push the gas pedal. Are you getting to that boost pressure easily?

A torn DV diaphragm has often been described as producing a “quacking” sound. I suspect you may have a defective DV.

You can check the DV holding ability by disconnecting the DV from the TIP. Plug the hole in the TIP but leave the port on the DV open. Then run a boost pressure test. The DV should be able to hold the boost pressure. If there is any air coming out of the open port on the DV you will need to replace it.

The reason you have to disconnect it from the TIP is because otherwise you are pressurizing it equally from both sides and consequently you will not be able to tell if it is capable of holding pressure.

[thomastollar]

Okay OG,

just did boost leak test as you suggested. First time around ran 15psi and after about a minute blew the PVC contraption off the TIP and scared the stuffing out of myself. Second time around 10psi, listening and feeling very carefully there is a very small amount of air escaping the DV (not sure if it matters in this case, but I do have the DV installed backwards).

Also, as a side note during leak test I hear a gurgling noise...is that normal?

Edit: Oh yeah, and with the wastage disconnected car was boosting much more easily and quickly...I did run it fairly modestly though as I read over-boosting could be accomplished quite easily without wastegate.

[old guy]

Been there, done that. Smacked my head with the PVC boost tester. Ouch!!

Gurgling noise is normal.

It sounds like your DV is holding OK. I believe the spring pressure on the 710N is around 6 psi. If the DV wasn't getting a proper boost adder or the diaphragm was torn you would have felt a significant amount of air coming from the open DV port.

When you ran requested versus actual boost I assume it was way off? Thus the underboost DTC. Beginning to sound like a sticky N75.

[thomastollar]

No kidding...maybe a pressure check valve on the PVC tester...its kinda of hard to be all stealth, listening for escaping air when there is the possibility of the thing shooting off loud as hell.

Okay:

gurgling noise - check.
DV - check
N75....I will run the requested vs. actual again right now and give you a specific answer to how far off it is.

[old guy]

No kidding...maybe a pressure check valve on the PVC tester...its kinda of hard to be all stealth, listening for escaping air when there is the possibility of the thing shooting off loud as hell.

Okay:

gurgling noise - check.
DV - check
N75....I will run the requested vs. actual again right now and give you a specific answer to how far off it is.

Also log the duty cycle of the N75 along with the boost logs.

[customa4]

I believe logging block 115 and 118 should cover the categories OG is looking for.

[thomastollar]

Did the logs, but cannot figure out how to get them to save in anything but .CSV files.
What I was able to notice in real time - on 115 things were okay until the boost request went over 17 then the actual could not follow.
Also, with N75 to wastegate actuator connected turbo spool sound is gone and boost is much slower to engage.

Will look into how to save logs into readable format.

[old guy]

Just copy and past the CSV file and I can probably figure it out. So far it is sounding more and more like a sticking N75.

Edit: Basically all I'm looking for is the N75 duty cycle in conjunction with the requested/actual. if the requested is above the actual and the N75 duty cycle is still high that would be an indication that the N75 isn't opening up all the way. You already confirmed that the turbo is capable of providing the boost and that the DV is capable of holding boost. That pretty much points to the N75.

Sometimes it's as simple as spraying a little WD40 or similar into the N75 while you activate it with a 12V signal and get it functioning properly.

[thomastollar]

OG - PM'ed the CSV's.

Will WD-40 the N75 tomorrow...the light is running out here for today.

[thomastollar]

WD-40'ed the N75 while using 12V to open and close it...the valve is at least operating well enough to open and close, and as fun and empower as it was to attempt to 'fix' once back on results were still the same...intermittent boost.

OG - PM'ed the CSV from todays logs 115 and 118....will post a sample here for curiosities sake.


,159.30,3840,81.2,1130.0,1440.0,159.13,3800,30.0,1 .2,1440.0,,,,,
,159.64,3840,78.9,1070.0,1440.0,159.47,3840,30.0,1 .2,1440.0,,,,,
,159.98,3880,74.4,1050.0,1430.0,159.81,3880,30.0,1 .2,1430.0,,,,,
,160.33,3920,73.7,1050.0,1400.0,160.16,3880,30.0,1 .2,1410.0,,,,,
,160.65,3920,74.4,1050.0,1430.0,160.49,3920,30.0,1 .2,1420.0,,,,,
,160.99,3960,73.7,1050.0,1410.0,160.82,3920,30.0,1 .2,1430.0,,,,,
,161.32,3960,74.4,1060.0,1410.0,161.15,3960,30.0,1 .2,1410.0,,,,,
,161.65,4000,78.2,1120.0,1430.0,161.49,3960,30.0,1 .2,1410.0,,,,,
,162.00,4000,80.5,1140.0,1460.0,161.82,4000,30.0,1 .2,1450.0,,,,,
,162.34,4040,82.7,1130.0,1460.0,162.17,4040,30.0,1 .2,1450.0,,,,,
,162.68,4080,81.2,1120.0,1460.0,162.51,4040,30.0,1 .2,1450.0,,,,,
,163.03,4120,79.7,1110.0,1450.0,162.86,4080,30.0,1 .2,1460.0,,,,,
,163.37,4120,80.5,1110.0,1450.0,163.20,4120,30.0,1 .2,1450.0,,,,,
,163.72,4120,60.2,980.0,1390.0,163.55,4160,30.0,1. 2,1450.0,,,,,
,164.06,4080,19.5,980.0,1240.0,163.89,4120,30.0,0. 0,1350.0,,,,,
,164.41,3920,15.0,980.0,1120.0,164.23,4000,30.0,0. 0,1170.0,,,,,
,164.75,3600,14.3,980.0,1060.0,164.58,3760,29.0,0. 0,1080.0,,,,,
,165.09,3000,26.3,980.0,1010.0,164.92,3000,29.0,0. 0,1050.0,,,,,
,165.44,3000,60.2,980.0,1060.0,165.27,3040,30.0,0. 0,1010.0,,,,,
,165.76,3000,70.7,1040.0,1150.0,165.60,3000,30.0,1 .2,1110.0,,,,,
,166.10,3000,72.9,1030.0,1270.0,165.93,3000,30.0,1 .2,1210.0,,,,,
,166.43,3000,73.7,1020.0,1320.0,166.26,3000,31.0,1 .2,1300.0,,,,,
,166.76,3000,72.2,1020.0,1340.0,166.60,3000,31.0,1 .2,1340.0,,,,,
,167.10,3000,74.4,1170.0,1340.0,166.93,3000,31.0,1 .2,1350.0,,,,,
,167.43,3040,86.5,1250.0,1380.0,167.26,3040,30.0,1 .2,1350.0,,,,,
,167.76,3040,89.5,1230.0,1420.0,167.60,3040,30.0,1 .2,1410.0,,,,,
,168.11,3080,91.0,1220.0,1430.0,167.93,3080,30.0,1 .2,1430.0,,,,,
,168.47,3080,90.2,1210.0,1430.0,168.29,3080,30.0,1 .2,1430.0,,,,,
,168.81,3120,88.7,1190.0,1430.0,168.64,3120,30.0,1 .2,1430.0,,,,,
,169.16,3160,86.5,1180.0,1430.0,168.98,3160,30.0,1 .2,1430.0,,,,,
,169.50,3160,88.0,1260.0,1420.0,169.33,3160,30.0,1 .2,1420.0,,,,,
,169.84,3200,92.5,1280.0,1430.0,169.67,3200,30.0,1 .2,1430.0,,,,,
,170.19,3240,94.0,1270.0,1440.0,170.01,3240,30.0,1 .2,1440.0,,,,,
,170.53,3280,94.7,1270.0,1440.0,170.36,3240,30.0,1 .2,1450.0,,,,,
,170.87,3320,94.7,1270.0,1440.0,170.70,3280,30.0,1 .2,1450.0,,,,,
,171.22,3360,95.5,1270.0,1450.0,171.04,3320,30.0,1 .2,1450.0,,,,,
,171.56,3360,94.0,1260.0,1450.0,171.39,3360,30.0,1 .2,1450.0,,,,,
,171.90,3400,94.7,1270.0,1450.0,171.73,3400,30.0,1 .2,1450.0,,,,,
,172.23,3440,94.7,1270.0,1450.0,172.07,3440,30.0,1 .2,1450.0,,,,,
,172.57,3480,94.7,1270.0,1460.0,172.40,3480,30.0,1 .2,1460.0,,,,,
,172.90,3520,93.2,1250.0,1460.0,172.73,3520,30.0,1 .2,1450.0,,,,,
,173.24,3560,92.5,1260.0,1460.0,173.07,3560,30.0,1 .2,1460.0,,,,,
,173.58,3600,91.7,1260.0,1460.0,173.40,3600,30.0,1 .2,1460.0,,,,,
,173.92,3640,92.5,1250.0,1460.0,173.75,3640,30.0,1 .2,1460.0,,,,,
,174.27,3680,92.5,1230.0,1460.0,174.09,3680,31.0,1 .2,1460.0,,,,,
,174.62,3720,91.0,1220.0,1460.0,174.44,3720,31.0,1 .2,1460.0,,,,,
,174.97,3760,90.2,1220.0,1460.0,174.80,3760,31.0,1 .2,1460.0,,,,,
,175.31,3800,90.2,1220.0,1460.0,175.14,3800,31.0,1 .2,1460.0,,,,,
,175.66,3840,88.0,1210.0,1460.0,175.48,3840,31.0,1 .2,1450.0,,,,,
,176.00,3880,89.5,1210.0,1460.0,175.83,3880,31.0,1 .2,1460.0,,,,,
,176.34,3920,88.0,1210.0,1460.0,176.17,3920,31.0,1 .2,1460.0,,,,,
,176.68,3960,89.5,1210.0,1460.0,176.51,3960,31.0,1 .2,1460.0,,,,,
,177.01,4040,89.5,1190.0,1470.0,176.85,4000,31.0,1 .2,1470.0,,,,,
,177.35,4040,86.5,1170.0,1470.0,177.18,4040,31.0,1 .2,1460.0,,,,,
,177.69,4080,86.5,1170.0,1460.0,177.51,4080,31.0,1 .2,1460.0,,,,,
,178.03,4120,87.2,1170.0,1460.0,177.86,4120,31.0,1 .2,1460.0,,,,,
,178.37,4160,85.0,1130.0,1470.0,178.20,4160,31.0,1 .2,1470.0,,,,,
,178.71,4160,28.6,980.0,1380.0,178.54,4160,31.0,0. 0,1390.0,,,,,
,179.05,4040,16.5,980.0,1180.0,178.87,4120,30.0,0. 0,1270.0,,,,,
,179.39,3840,13.5,980.0,1090.0,179.22,3960,30.0,0. 0,1130.0,,,,,
,179.73,3160,15.0,980.0,1050.0,179.56,3640,30.0,0. 0,1070.0,,,,,