Quick question about N75 valve

V

Vipaz

Member
Joined
Jun 4, 2018
Location
Lithuania
TDI
Golf MK4 1.9 81kw
Hey all, just a quick question about N75 valve:
Log starting at 3rd gear ~1200rpm with one N75 valve: https://log.malonetuning.com/chart/240632#H8KLCABBY8OMWwIDTcOLw5EKwoMwDMKFw6F3w4l1A1PDtjbCpRfDkcKGGnDCrcKkw6lwe8O6WcKFw6HDpcO5DsK%2Fw7cwwpfDlyTCmTFpaVsFw7cIwq7Do1pUwr58TAfCiTMrGcODw7XDpDfCq8KhFcOcwpF2w6nDhcOVUMKMw7jDuRPCqMKkw4XDjsKkwrLDnQ4%2FBgfDg3lQwrNSwrdVwqzDu8Oww6zCtEhkwoxkdERdR2fDmjjChB9Mw7svwqzCqQAAAA%3D%3D , with another N75 valve: https://log.malonetuning.com/chart/240631#H8KLCABtXsOMWwIDTcOLw5EKwoMwDMKFw6F3w4l1A1PDtjbCpRfDkcKGGnDCrcKkw6lwe8O6WcKFw6HDpcO5DsK%2Fw7cwwpfDlyTCmTFpaVsFw7cIwq7Do1pUwr58TAfCiTMrGcODw7XDpDfCq8KhFcOcwpF2w6nDhcOVUMKMw7jDuRPCqMKkw4XDjsKkwrLDnQ4%2FBgfDg3lQwrNSwrdVwqzDu8Oww6zCtEhkwoxkdERdR2fDmjjChB9Mw7svwqzCqQAAAA%3D%3D
Seems that with another N75 it boost better ? I'm right ? I mean that I can even feel while driving.Problem is that my car is sluggish at low RPM, MAF is ok, turbo have been rebuilt.Those are used N75 valves, I don't want to waste money on new one so I'm trying to figure out if N75 can be sluggish ? No fault codes/no limp mode.Actuator rod moves freely when using VCDS N75 test ( with both N75 valves).
 
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eddieleephd

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Location
Battle Ground, Wa
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2002 jetta Wagon
That's a crazy boost log. I would say that you need to be looking at the actuator and the lever to see if turbo is sticking open.
The overboost looks safe, 130 over isn't bad, however, the shape of the line and that it doesn't come below the requested says to me that the lever isn't moving as it should.
N75 vent line can be clogged, and so can the one to the actuator.
Also check the actuator for a vacuum leak to be sure it's good.

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V

Vipaz

Member
Joined
Jun 4, 2018
Location
Lithuania
TDI
Golf MK4 1.9 81kw
eddieleephd said:
That's a crazy boost log. I would say that you need to be looking at the actuator and the lever to see if turbo is sticking open.
The overboost looks safe, 130 over isn't bad, however, the shape of the line and that it doesn't come below the requested says to me that the lever isn't moving as it should.
N75 vent line can be clogged, and so can the one to the actuator.
Also check the actuator for a vacuum leak to be sure it's good.
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Click to expand...
I have a video how my actuator moves with VCDS test, here is it: https://www.youtube.com/watch?v=dmMima9jKfA
Any comments ?
Anyway let's say it's a problem with actuator lever or sticking turbo, how then my car runs perfect on highway at high rpm ? I mean as you can see from lines in log the boost from ~2000rpm are quite similar even though as you say it overboost a little, but as I said, car runs very good at 2500-3000rpm range at highway.

Btw, I don't know if I be able to check for actuator leak, cause I know that I need a hand vacuum pump but in my country there is no such a thing to buy or they costs a lot( like more than 100€ ).
 
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eddieleephd

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May 27, 2012
Location
Battle Ground, Wa
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2002 jetta Wagon
Yeah, you would have to have a pump of some sort. However, you can make one with a bit of engineering and a vacuum/pressure gauge.
I would use two vacuum check valves and some PVC, or other tube to create the pump. Put a vacuum check valve ahead of a T, the gauge to the T, and T to actuator. This way you can measure the vacuum created.
Now with pvc, or other tube you need to create the pump. You need to get 18 lbs of force capability so you can either find a ball that you can hook up to the vacuum line with valve and put the other valve behind it, or find a way to create a plunger in a tube with the same capability.
Pvc in pvc with the correct parts you can make it happen. I'm thinking of the slip joint ahead of the p trap in a sink drain that uses the triangular seal. Cap one end and hook to vacuum lines, loosening the slip joint enough to slide easily enough, cap the other end and hook up the other one way valve (vacuum check valve).
My first Nick name was McGuyver because of things like this. I would create one and try it myself if I had all the parts.
The below image is of the parts that are needed to create the pump seal. You will also need a piece of pvc for the pump body and a couple caps with 4 mm, 1/8" nipples to fit vacuum lines and valves.

Below is the assembly of the seal.

I recommend the flanged tube be 18in 45-46cm long and 6-9 in 15-24cm shorter for the larger pipe that glue's to the screw around the flanged tube. Cap both with vacuum outlets and use one way valves in the same direction, black facing the vehicles vacuum system. Enough vacuum tube to connect to the vehicle and not pull apart when pumping.
I would use the vacuum check valve on the car side to release pressure as they easily disconnect avoiding further need for engineering.


The flange will fit inside the exterior pipe helping to keep it straight, and a little engine oil will promote the sealing and sliding of the pump itself. Likely that you will want to sand the outside of the flanged tube to make it smooth and slide well.
I will have to make one for myself soon to see how well I can get it to work. I love to create things like this.
The plunger in a mighty vac is only an inch or so wide and spring loaded, they tend to be weak and the design above is likely to create more vacuum more easily.
 
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V

Vipaz

Member
Joined
Jun 4, 2018
Location
Lithuania
TDI
Golf MK4 1.9 81kw
eddieleephd said:
Yeah, you would have to have a pump of some sort. However, you can make one with a bit of engineering and a vacuum/pressure gauge.
I would use two vacuum check valves and some PVC, or other tube to create the pump. Put a vacuum check valve ahead of a T, the gauge to the T, and T to actuator. This way you can measure the vacuum created.
Now with pvc, or other tube you need to create the pump. You need to get 18 lbs of force capability so you can either find a ball that you can hook up to the vacuum line with valve and put the other valve behind it, or find a way to create a plunger in a tube with the same capability.
Pvc in pvc with the correct parts you can make it happen. I'm thinking of the slip joint ahead of the p trap in a sink drain that uses the triangular seal. Cap one end and hook to vacuum lines, loosening the slip joint enough to slide easily enough, cap the other end and hook up the other one way valve (vacuum check valve).
My first Nick name was McGuyver because of things like this. I would create one and try it myself if I had all the parts.
The below image is of the parts that are needed to create the pump seal. You will also need a piece of pvc for the pump body and a couple caps with 4 mm, 1/8" nipples to fit vacuum lines and valves.

Below is the assembly of the seal.

I recommend the flanged tube be 18in 45-46cm long and 6-9 in 15-24cm shorter for the larger pipe that glue's to the screw around the flanged tube. Cap both with vacuum outlets and use one way valves in the same direction, black facing the vehicles vacuum system. Enough vacuum tube to connect to the vehicle and not pull apart when pumping.
I would use the vacuum check valve on the car side to release pressure as they easily disconnect avoiding further need for engineering.


The flange will fit inside the exterior pipe helping to keep it straight, and a little engine oil will promote the sealing and sliding of the pump itself. Likely that you will want to sand the outside of the flanged tube to make it smooth and slide well.
I will have to make one for myself soon to see how well I can get it to work. I love to create things like this.
The plunger in a mighty vac is only an inch or so wide and spring loaded, they tend to be weak and the design above is likely to create more vacuum more easily.
Click to expand...
That looks so cool! Thanks for writing this, I'm also like to make similar things so maybe I will try to make it whenever I have free time..Anyway what are you though about actuator video that I posted ?
 
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eddieleephd

Top Post Dawg
Joined
May 27, 2012
Location
Battle Ground, Wa
TDI
2002 jetta Wagon
The actuator seems to be moving fine, however, it's not representative of the subtle movement needs for boost control. These can really only be felt with the finger tips.
The small ones that can be more effected by the actuator sticking.
Overall I think it's fair and would recommend checking the ambiant pressure against map pressure readings to ensure they match with the engine off.
If the map sensor is not reading properly then boost values are out of spec and readings are not correct.
Not having my eyes and hands on it it's really difficult to tell.

In my experience the stated adjustment is only viable installing a new actuator.
Really the vacuum actuator should start moving at 5mbar and stop around 18mbar. Otherwise, the actuator is bad.
As far as adjustment of the length goes, trial and error with logs for review and readjustment is the best way.
Any modifications to the fueling, or the exhaust can effect how quickly the spooling occurs and this changes the desired position of the actuator adjustment directly.
Factors driving boost are exhaust gas causing the spin(adjusted with IQ, mapping, and nozzles), exhaust restriction slowing down the gas(changes with clogging cat, reduced with upgraded exhaust), angle of the fins catching the exhaust gasses (what we adjust with actuator).

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E

eddieleephd

Top Post Dawg
Joined
May 27, 2012
Location
Battle Ground, Wa
TDI
2002 jetta Wagon
Basically the N75 is actuated with voltage. The valve is fully open at a set voltage and closed at another. The percentage of the voltage applied by the ECM is what's shown by the computer.
The computer uses assumed values based on stock hardware and cannot actually measure the percentage of vacuum actually being applied, just as it cannot measure the injected quantity of fuel. It compares values expected to values actually available in the map to adjust it's request.
If the n75 valve isn't with operation parameters then it's not able to be controlled effectively, or to control boost effectively.
Leaks in the valve or vacuum system in general affects the operation of the boost.

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C

Curious Chris

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Jun 11, 2001
Location
Pineview GA
TDI
Jetta Wagon 2003 RIP Rockford IL
eddieleephd said:
Basically the N75 is actuated with voltage. The valve is fully open at a set voltage and closed at another. The percentage of the voltage applied by the ECM is what's shown by the computer.
The computer uses assumed values based on stock hardware and cannot actually measure the percentage of vacuum actually being applied, just as it cannot measure the injected quantity of fuel. It compares values expected to values actually available in the map to adjust it's request.
If the n75 valve isn't with operation parameters then it's not able to be controlled effectively, or to control boost effectively.
Leaks in the valve or vacuum system in general affects the operation of the boost.

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Click to expand...
The ECM sends Pulse Width Modulation voltage that moves the plunger in the N75 to reach the boost specified .
 
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