How do you know your wastegate actuator diaphragm is damaged?

[ROH ECHT]

How do you know your N75 or wastegate actuator diaphragm is damaged?

I have been trying to help another GTI owner in our Tuner Club with boost issues. His data shows that actual boost does not reach specified until rpm's go over 5200 regardless of preload on the rod adjustment. Once boost is met with desired/specified, beyond 5200 rpm, his specified is 2.0 bar(minus atmosphere) and actual can remain above desired boost. His actuator rod spins quite easily when I was adjusting it with vise-grips attached to the rod and so I suspect the actuator diaphragm is damaged. Have any of you gone through this exact process? And, am I on the right track suspecting the actuator diaphragm?

I asked my Tech if he can test it and he can. He also said it doesn't matter whether he applies pressure or vacuum to do the test. Is he right? Or do I need to determine which will perform the test appropriately?

Points to consider:
I found no leaks
N75 should be in good nick given it does create boost
DV is not ruptured as it does hold boost once desired is achieved...even at a minimal amount of actuator preload of 2mm.

 

[gti2slow]

Pull a vac with a handheld pump (I use a Mityvac) on the actuator itself, it should hold vac, if not there is a leak.

I would look at the n75 valve before the wastegate actuator.

 

[ROH ECHT]

↑ :thumbsup:

How would I test his N75? I can do the vac hold test on the diaphragm...not sure on the N75 though :/

I just found this: the long part of the "T" which is connected to the intake tube before the turbo SHOULD NOT leak if you blow air into the other 2 nipples. If it does AT ALL you need a new one...if you take a resistance reading between the 2 prongs in the plug it should be between 25-35 ohms.

Another thing I should check..is swap out my MAF into his.

 

[gti2slow]

Not really sure how to test operation, just a good inspection because those grey plastic barbs do crack over time.

 

[ROH ECHT]

Right on...think I will suggest to test the diaphragm with vac and try the bit I found on the N75 test next time. I will hopefully have a solution to post when or if found for future reference.

 

[donjuan1jr]

We have a reference for testing the different n75 valves, I'll see if I can get the pic for u.

Lazy mans version

Top #1 port should hold vacuum.
Middle #3 port should NOT hold vacuum.
Bottom #2 port should hold vacuum until #3 middle port is disconnected and then pressure will drop.

 

[ROH ECHT]

↑:thumbsup:

 

[donjuan1jr]

Top and middle would be the plastic ports, bottom is that brass.

 

[ROH ECHT]

:thumbsup:
Great...thanks!

 

[ROH ECHT]

We tried my MAF and no difference was made. Testing the N75 and WG is next. I will report...also going to post a graph of his boost for future reference.

 

[ROH ECHT]

Tested both WG actuator and N75...both held vacuum. I feel that the WGA needed to be tested under pressure instead of vacuum, but don't know how much the internals differ from my own Forge. Running out of ideas now.

 

[ROH ECHT]

Decided to look at the vac test again and both the WGA and N75 held...but the ohm test on the N75 came up at 23ohm and not between 25 and 35. We replaced the N75 and everything works perfectly. His boost, from peak to redline, is 20-21 to 17-18 psi.

Problem solved finally. My guess is that visually physically nothing was wrong with the N75, but the circuitry was failing or on the way out. It showed sign of a good amount of oil residue in the N75 ports as well...perhaps causing this to happen.