N75 vacuum testing question

[roadhard1960]

I have my Mity Vac with a vinyl hose. I put my finger on the hose and pump to about 25" and it holds that vacuum. I attach it to the black port on the N75 and put my finger on the two white ports. It bleeds down pretty fast. Is the N75 supposed to hold a vacuum in this test? I would hope so as it would seem that the device at the end of the white ports would not getting the proper amount of vacuum. I also tried to attach the vacuum to the large white port and cover the remaining ports and I get the same quick leakdown. That would be about 4 seconds to go from 20" to zero. Note that the Mity Vac cannot get 25" like it does with the finger test.

I am wondering if my weird throttle stuff that I did not notice 150,000 miles ago when I had the car chipped is related to this N75 having an internal vacuum leak.

 

[sdeck]

just posted the exact same question. Mine does the same thing. Not sure if it is normal (I suspect not), but if it is bad, it could explain my dismal power.

Anybody know this answer?

 

[roadhard1960]

Well my car has no lack of power. It smokes like crazy as I cannot get the IQ to adjust where I want. Well it only smokes at moderate and heavy throttle.

The weird surge I have depends on throttle position. I have not figured out exactly where it is but some days I keep hitting it. I guess the days I hit it I am not driving egg footed.

There are a number of threads on frozen turbo linkage. Some related to the internal linkage getting frozen up. Ohters related to the actuator going bad. The turbo internal linkage looks like a bit of drama to fix. The actuator looks relatively minor to repair.

No power can come from bad Mass Air Flow sensor. It can come from a clogged intake. It takes somewhere about 100,000 miles or so to really gunk up the intake. Clean freaks will clean the intake the same time they are doing the 100,000 mile tining belt and water pump.

On my car I can hear the turbo spool up easily when the windows are open. Not so easy when the windows are closed. I guess my bad hearing is not real bad in the turbo frequency yet. If you are not deaf then listen for the turbo noise.

Right now I am at the ask questions and spend no money stage. The weirdness can hang for a few months or more as it is not that bad. The IQ and smoke bugs me but not to the tune of hundreds of dollars for a different chip. I like the Banks diesel power advertisement where they do so crazy fast drag strip stuff without a huge black cloud.

 

[sdeck]

I just installed Sprint 520s in my '03 auto as well. Smoked like crazy, but had lots of power. Funny thing is the MAF actual still wouldn't get above 500 or so regardless of requested. MAP seems OK, lags a bit but gets to the requested boost pressure. Dialed up the IQ as high as it could go in VAG-COM (32645, 5.8/6.0) and the smoke is now almost reasonable, but power is down significantly. I have gone thru all of the low-power stuff: new MAF, VNT is smooth and travels 3/4", turbo vac line is solid, vac in system is 25", clean intake/EGR, new air filter, new fuel filter, cleaned snow screen. N75 clicks very softly during output test, but like yours, it will not hold vacuum when isolated. That makes me wonder if it is bad. Near as I can tell, the top white port is the vac supply, the bottom white port is the VNT line, and the black port is the vacuum relief.

If you plug two and vac the third, shouldn't it hold vac?

I can't believe nobody has tried this.

 

[Deevo_3000]

I'm also wondering....

BUMP

 

[roadhard1960]

Well it humors me to no end some of the geek stuff people know but this simple question remains unanswered. I guess I need to buy a new N75 to answer the question. OK, in the spirit of science I ordered a new one from TDIParts.com. Maybe I will have an answer next week. I doubt the postal service will have it here by the weekend. Of course it will arrive faster than the parts I ordered from Germany and Ireland. Coming up on 3 weeks to a month on those parts and still no sign of them. ;-(

 

[sdeck]

If the winds calm down tomorrow, I will try to get to the EGR valve and check that one. I'll wait to order an N75 until you post that it cured your problem

 

[roadhard1960]

http://www.haywood-sullivan.com/vanagon/TDI/tdi-technik-eng.pdf
This a great article. I have an electronic Bentley. In days of old the paper manual would sometimes explain how things work.

 

[sdeck]

I pulled the N75 and EGR valve and tested both with a Mityvac. N75 could not hold vacuum when pulled in vac port and other ports blocked off. EGR valve held vac much better, but still bled down slowly. I switched them and went for a drive. No change in performance. Still low power, smoking under acceleration. MAP looks good, MAF sucks. see graphs below (rpms on right). This is a new MAF and I have done everything I can think of(new air filter, clean snow screen, new fuel filter, clean intake/EGR, checked case pressure relief valve, VNT moves smoothly ~3/4 inch under vac and mityvac, timing is OK) short of dropping the exhaust. (That's coming, just need time, but I am not convinced that could explain the low MAF readings)

Also, during an N75 test cycle with the EGR valve controling the VNT, the system pulls 24-25" Hg. At idle, there is about 15" in the line.

How long can I leave the valves switched?

Any other suggestions? Here are the latest straws I am grasping at:
Could a weak battery cause this??????
clogged intake ports??????

 

[alphaseinor]

low maf (say under 500) says you are at a higher altitude.

 

[sdeck]

Is that really all it is? I have been tearing my hair out for a month trying to get more air through the system. I can't believe there isn't some kind of compensator through the atmospheric pressure sensor. I live at about 5200 feet. Not real high.

I used to have power and thought the P520s would help. Is it possible they won't work at this altitude? It really isn't that high!

 

[lekolite]

I have a similar question. I was testing vacuum today and noticed the vacuum reservoir was empty after sitting for a few minutes. Reservoir holds vacuum, rest of system does not. I was assuming I had a cracked hose(s), but that may not be the case if the N75's won't hold vaccum on their own. Anyone know if those vacuum valves hold out of the box?

 

[roadhard1960]

You will not find residual vacuum after a few minutes. New N75 is in the mail. Basic testing to be done soon.

 

[Lefty]

Is that really all it is? I have been tearing my hair out for a month trying to get more air through the system. I can't believe there isn't some kind of compensator through the atmospheric pressure sensor. I live at about 5200 feet. Not real high.

I used to have power and thought the P520s would help. Is it possible they won't work at this altitude? It really isn't that high!

I too live at about 5400 feet but I know most people live closer to sea level or about 1000 ft and less. So remember 5200 ft is high altitude. I'm sure he didn't mean 14,000 ft.

 

[sdeck]

Yeah, but is that higher enough to cause this kind of problem? My power kind of dropped away over several months and after borrowing a VAG-COM, the only thing I can find that is not right is that air actual is well below the air requested. MAP is fine. Can't figure it out.

 

[sdeck]

Hey RoadHard, any news on the new N75 vacuum worthiness? I checked my EGR valve and it lost vac slowly, no where near as quick as the N75 (it wouldn't hold more than a few seconds). I am still running my N75 and EGR valves switched.

 

[roadhard1960]

25" at vacuum in. Plug on out. 10 seconds to bleed down. Also plug the the manifold pressure in port and the bleed down takes over 20 seconds. Apply MityVac pressure port to pressure port on N75 and air pumps out. I need to hook up a better air source in tomorrow to test.

I need to compare directly with the existing 5 year old one. I do suspect that there is no airtight anything between the ports. I need to do some more experimenting and measuring tomorrow.

Last weekend my pump sprung a leak. I had been reading about the issue the past two weeks so it was no huge shock or cause for concern. I ordered an oring install kit and a pump reseal kit from Dieselgeek Sunday night. Seals were at the house Wednesday. I had that oring changed that night and the mess cleaned up. $10 versus $900 or worse for a rebuilt one. Given that the seals are $30 there must be a bit of labor to replace the seals and test. That distracted me from other obsessions.

Hey as a side note, before I discovered that oring leak the car tone would change within about 5 seconds of starting. I thought it was just valve lifters pumping up. The change in sound was sort of like the change you hear when you are doing an IC adaptation. After the oring change the car is starting a bit quicker and the tone does not change. Interesting symptoms and byproduct that no one mentioned.

 

[sdeck]

Try the Mityvac on vac in and plug the other two ports. Mine won't hold when I do that.

 

[roadhard1960]

Reread my post. ;-) I said when I pull 25" on the vac port and I plug the big white port it takes about 10 seconds to leak down. When I plug the big white port and the black manifold pressure port it takes about 20+ seconds for the 25" to leak down.

 

[CTD&TDI]

so what is the right way to test? apply mityvac to port "?" and block port x and y?

 

[sdeck]

Just to keep my head straight:

top white = small white = vac in

bottom white = large white = VNT actuator

black port = manifold pressure port = bottom of air box (I don't think this actually gets any pressure, I think it just allows relief of the vacuum when the valve cycles off (could be wrong though)

 

[CTD&TDI]

so test would you apply vac to top left port, block off port going to actuator and leave the black port open? or block it off as well?

 

[roadhard1960]

What does the Bentley say about the test? My Bentley has you checking resistence. It has no spec for leakdown. I just posted the observed leakdown numbers on a new N75 with various ports plugged for reference. What have you observed with the ports blocked as I did?

I believe that the black port is just a vent as sdeck suggests as does the Haywood article. I believe it is attached to the intake just to keep the valve clean.