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Old December 21st, 2017, 12:46   #1
Palka3
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Default Sticking actuator or faulty N75 solenoid?

I was driving my Jetta to a meeting. After filling up with diesel I was merging onto the interstate. While merging onto 75mph traffic I felt the car jerk slightly. The Engine light came on shortly after that. I turned around and swapped vehicles.
A Scan stated it was the Turbo. I didn't think so because the car never went into "limp mode"
I've read thru the forum and narrowed it down to the vacuum lines. I replaced the original vacuum lines (180K miles) to both EGR(N18) and boost(N75) valve. The actuator tested OK under vacuum. The linkage at the turbo was lubricated while I was there. The engine light went away (on its own) after the vacuum lines were replaced.
Yesterday the same thing happened on a 275 mile trip. I noticed it occurs around 70-75MPH when merging or climbing a hill or passing another vehicle where boost is needed. It's almost like the actuator or boost valve is sticking when it gets to a certain value. I don't have a EGT or boost gage to determine if there is a change before of after this event.
Any help would be appreciated.
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Old December 21st, 2017, 13:10   #2
JB05
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What was the actual DTC(digital trouble code)? Chances are it is still stored in the ECU.
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Old December 21st, 2017, 15:09   #3
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Yeah, saying "it was the turbo" is not enough information for you to get a real diagnosis...
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Old December 21st, 2017, 15:26   #4
Palka3
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P0235 as read from AutoZone. The funny thing is I was taking the car to a friend that has a VAG COM when the code cleared itself. I suspect there was a vacuum leak and it took a little time for the ECM to reset and clear the code.
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Old December 21st, 2017, 15:47   #5
Palka3
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To clear up my last post. I still have a check engine light.

I've read that you can clean the solenoid with carb / electronic contact cleaner. Where would you be spraying?

Each port?
Isn't that just cleaning both sides of a diaphragm? Maybe the solenoid is sealed. If not, then the cleaner might loosen up the rod that controls the operation of the diaphragm.

The other location to spray would be the electrical connections. Maybe the contact points are dirty and giving a false signal to the solenoid.
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Old December 21st, 2017, 15:58   #6
BobnOH
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A light cleaning of the N75 could help, normally they don't get dirty, takes some contaminent into the vacuum system.

From Ross Tech wiki-
Possible Causes
Hoses/Pipes incorrect connected, disconnected, blocked or leaking
Charger Pressure Control defective
Solenoid Valve for Boost Pressure Control (N75) defective
Turbocharger defective
Possible Solutions
Check Hoses/Pipes to/between Components
Check Charge Pressure Control
Check Solenoid Valve for Boost Pressure Control (N75)
Check turbocharger
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Old December 21st, 2017, 15:58   #7
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Get a MityVac or similar and apply vacuum to the actuator and check to see how smooth the rod moves. If you apply full vacuum till it hits the stop and then release, it will give you a good indication if that's your issue. Sticky vanes can certainly cause overboost.
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Old December 22nd, 2017, 19:32   #8
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Quote:
Originally Posted by Palka3 View Post
I've read that you can clean the solenoid with carb / electronic contact cleaner. Where would you be spraying?

The other location to spray would be the electrical connections. Maybe the contact points are dirty and giving a false signal to the solenoid.
I took the N75 off, sprayed a bit of penetrating oil in each port, then shook it and lightly blew air to each port.
The car did seem more responsive for several days.
I did finally replace it.

I've read you use dielectric grease in the plugs and sockets.
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Old December 23rd, 2017, 00:02   #9
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Good thing you replaced it . Penetrating oil would have most likely destroyed the diaphragm over a short time.

I almost never use dielectric grease except maybe on light sockets because most automotive connectors are waterproof.
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Old December 26th, 2017, 21:00   #10
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PLEASE wear eye protection if you are taking of the N75 and spraying it to clean it with anything (compressed air/brake cleaner). I did that to mine and in a "I don't NEED no safety glasses man-moment" got blasted by carb cleaner in the eye, Not fun, thankfully no permanent damage.

On the testing of the actuator, the advice of using a mityvac or equivalent is golden. But before you buy/borrow one, get under the car and move the actuator lever with your finger or a screwdriver (its a strong spring! but you can do it). I heard a "crunch-crunch-crunch" rust sound as I was moving it with my hand and knew instantly:

1. Regardless of if my vacuum system did/did not have a leak, the smart actuator HAD to be replaced.

2. The N75 SHOULD be replace (since rust contamination was in the system), didn't want to kill the new actuator in a few weeks/months

3. The vacuum lines SHOULD be replaced

I did all three.
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Old December 27th, 2017, 00:16   #11
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Quote:
Originally Posted by VincenzaV View Post
"I don't NEED no safety glasses man-moment" got blasted by carb cleaner in the eye, Not fun, thankfully no permanent damage.
Not all of us are as bright as you
*puts ear up to the end of the garden hose tell if the water is coming
>ear infection for 3 months
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Old December 27th, 2017, 15:43   #12
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Quote:
Originally Posted by VincenzaV View Post
2. The N75 SHOULD be replace (since rust contamination was in the system), didn't want to kill the new actuator in a few weeks/months
Never heard of that one before. So how exactly does "rust contamination" get into a vacuum system? How did the rust get contaminated?
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Last edited by Ol'Rattler; December 27th, 2017 at 15:45.
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Old December 28th, 2017, 11:54   #13
flee
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Quote:
Originally Posted by Ol'Rattler View Post
Never heard of that one before. So how exactly does "rust contamination" get into a vacuum system? How did the rust get contaminated?
IDK if it's really a thing but it's not that hard to imagine a failed (rusted open)
actuator letting in some debris, including rust particles.
As far as replacing the N75 though, I've had good luck blowing out a bit of debris
just using compressed air. Original one from 2002 still working.
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Old December 28th, 2017, 12:18   #14
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Quote:
Originally Posted by Ol'Rattler View Post
Never heard of that one before. So how exactly does "rust contamination" get into a vacuum system? How did the rust get contaminated?
Broke vac pump can let in some crankcase gas, half cleaned EGR,n75,etc. could introduce rust bits, unconnected vacuum tubes. Actuators rust out but usually stay clean on the vacuum side.
I thought this was odd as well, but a few have reported various contamination of the vacuum system.
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Old December 28th, 2017, 21:29   #15
VincenzaV
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The actuator rusted out, pure and simple.

As far as the N75, Not sure how, but after it shot at my eye, I was able to use compressed air and hit the N75 and see little rusty bit in my hand from the N75.

Not sure if actuator rusted through inside completely (could explain the crunching rust noise), or were it came from.

It's all good now though!
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