Black and white check valve to n75

[POWERSTROKE]

Can this cause an over boost if it’s bad? I can suck and blow (yeah I know) on both ends of this thing....

 

[oilhammer]

It will cause NO boost from my experience, although I have only come across a couple of those bad over the years.

OVERboost is generally caused by either a sticking VNT mechanism on the turbo, or the N75 itself unable to vent away the vacuum properly, and allow the VNT actuator to return to the rest position.

 

[BobnOH]

Did some quick searching, one member restored his by cleaning.
But here is the answer (yes) +
https://forums.tdiclub.com/showpost.php?p=3866650&postcount=10

 

[JETaah]

That check valve isolates the N75 and the vacuum ball reservoir from influence of other components using vacuum.

If it does not work properly then the N75 valve may not have enough vacuum on hand to pull the vane lever actuator where it needs to go. Underboost, not overboost is the result.
If you sit there madly pumping the brakes, I suppose that you could thwart its capacity to keep a steady vacuum supply to the input of the N75 valve.
I often enough find the B/W check valve faulty when a turbo actuator develops a hole in the diaphragm and rust debris and dirt get sucked all the way back to the vacuum pump. The small nipple on the brake booster check valve assembly attached to the vacuum pump can get clogged as well as the N75 valve.

 

[POWERSTROKE]

It will cause NO boost from my experience, although I have only come across a couple of those bad over the years.

OVERboost is generally caused by either a sticking VNT mechanism on the turbo, or the N75 itself unable to vent away the vacuum properly, and allow the VNT actuator to return to the rest position.

I did the output test in vcds on the n75. In my other thread I noted it would make sort of a chirp sound and the normal thump thump. How can you tell if the thing is actually bad? My overboost happens rarely, and only on long hill climbs. Happened last Saturday doing a steady 85mph up a long grade on I-91. Them I can pound on the car incessantly on the flats and runs like a champ.

Is there a way to verify for sure a bad n75?

 

[POWERSTROKE]

That check valve isolates the N75 and the vacuum ball reservoir from influence of other components using vacuum.

If it does not work properly then the N75 valve may not have enough vacuum on hand to pull the vane lever actuator where it needs to go. Underboost, not overboost is the result.
If you sit there madly pumping the brakes, I suppose that you could thwart its capacity to keep a steady vacuum supply to the input of the N75 valve.
I often enough find the B/W check valve faulty when a turbo actuator develops a hole in the diaphragm and rust debris and dirt get sucked all the way back to the vacuum pump. The small nipple on the brake booster check valve assembly attached to the vacuum pump can get clogged as well and the N75 valve.

So I know I need a check valve. I have had 2 rusty actuators so far. I installed the third last fall. Is it best to replace the check valve and n75 for what I describe? The actuator hood vacuum and seems to go down smoothly.

 

[BobnOH]

Almost sounds like there is a bunch of crap in your vacuum system.

 

[POWERSTROKE]

All the lines were replaced.

 

[Mongler98]

Was there any oil in the old lines when you took them off?
It might be worth doing an oven cleaning to the vtn

 

[POWERSTROKE]

No oil....

 

[POWERSTROKE]

I actually cleaned that check valve out with wd-40 as the other post suggested and it seems to be working properly now.. ��

 

[oilhammer]

If you have suffered rusted out VNT actuators, then your vacuum system has ingested some debris. There is no doubt about it. Where that debris ends up is usually the ying-yang valve (the black and white check valve) and the N75 valve. Sometimes you can blow them out and clean the stuff out, sometimes it gets jammed in there in such a way that you cannot, and you need to replace the part.

 

[POWERSTROKE]

Thanks guys. Maybe the best bet is to replace those two units, or watch and wait at this point. ....

 

[JETaah]

It will let you know if it is not working.

 

[flee]

It's not difficult to bench test the N75 valve by connecting it to a low pressure air
supply (15psi max) at the vent nipple and cycling it with 12VDC.
I was able to clear a bit of debris from my N75 this way.