Testing the N75 Valve

S

Steve777

Veteran Member
Joined
Dec 1, 2003
My 01 ALH Golf has been going into limp mode and generating code 17965 - Charge Pressure Control: Positive Deviation Intermittent. So I read up on this problem, and think it may be the N75 valve. Here's what I found:

Turbo actuator/lever move when vacuum is applied via a Miti-Vac. Seems to move at the right vac levels, not entirely sure if I am getting full travel, as I was testing this with one hand on the actuator lever and one on the miti-vac. But it moves and holds pressure and position.

Overall Vac is OK not great (about 20in per the mitivac gauge). Think it might be my vac pump as it is getting old (~300K miles), but need to get a know accurate gauge to double check.

I pulled the N75 and am trying to test it, but am having difficulty in finding out what exactly it is supposed to do. When off the car no power to it, It seems the main vac and out lines are connected. But I can also blow into the relief port and get some but not full flow thru there too??? (all this testing by mouth so no extreme pressures here)

I was thinking the N75 should be a switch, the out port connected to either the vac port or the relief port 100% depending on power to it, none of this part way stuff. Is that right??? Seems like my N75 is leaking a bit between the relief and vac ports when no power is on it.

Does anyone know for sure what flow should and should not be with this valve?

TIA
 
B

bbarbulo

Veteran Member
Joined
Jan 11, 2003
Location
Windsor, ON, Canada
Test resistance, I was getting about 16 ohms iirc across the EGR solenoid. N75 should be the same. I plugged both outs, and applied vacuum on the in. Then took my fingers off the outs. Did this a few times, and the sound changed... Like it was stuck before and now not anymore. And its been working great and no codes. Again, this was the egr and not n75, but same concept. I think I have a spare n75 if you think you need one.
 
S

Steve777

Veteran Member
Joined
Dec 1, 2003
Thanks. Yeah the coil resistance tested at ~20 ohms so comparable. I did test it by connecting the coil to a battery and found that it did make a clicking sound as well as change the flow characteristics when energized.

I would just like to hear if this valve is supposed to be all one way or the other, or if it is supposed to have some minor leaking of air between the two paths when it's good.
 
Matt-98AHU

Matt-98AHU

Loose Nut Behind the Wheel Vendor
Joined
Apr 23, 2006
Location
Gresham, OR
TDI
2001 Golf TDI, 2005 Passat wagon, 2004 Touareg V10.
CoolAirVw said:
Best way to check is to do output tests with vag com with a vacuum guage on the output of the n75.
Click to expand...
Winner right here.

Put a vacuum gauge to the VAC OUT port, start the car, run basic setting 11 or N75 output test, see how much vacuum it puts out. When it switches to "off" it should be 0 vacuum. When it switches to "on," it should be the same amount of vacuum the rest of the system has (which in your case sounds like about 20" mg. A really healthy system will do 25" or more).

With that having been said, too little vacuum is a recipe for underboost, not overboost...
 
You must log in or register to reply here.
Top