How many people are seeing N75 units go bad or intermittent way too often ? I seem to have one bad every year, when it gets cold out I have to reset mine by turning off the ignition for a moment then the boost comes back , I would love to find a electronic method of controlling the boost on these cars .
Defective N75 units
- Thread starter akal65
- Start date
burpod
teh stallionz!!1
- Joined
- Nov 27, 2004
- Location
- cape cod, ma
- TDI
- 82 rabbit vnt ahu, 98 jetta vnt ahu, 05 parts car, 88 scirocco.. :/
are you sure it's actually the valve? take logs? when cold weather hits, depending on your state of tune + fueling hardware (bigger nozzles?) timing in the tune could be advancing, target boost could be being reduced, air is denser, and depending on how well everything is done for your hardware, that can be a reason for boost issues... lots of stuff can be going on you aren't aware of
The boost just dies , this happens when it gets around 1 or 2 degrees. by shutting off the engine and restarting it resets and all is well . what logs are you wanting me to take ?
burpod
teh stallionz!!1
- Joined
- Nov 27, 2004
- Location
- cape cod, ma
- TDI
- 82 rabbit vnt ahu, 98 jetta vnt ahu, 05 parts car, 88 scirocco.. :/
probably best to take 011-001-004 and note the ambient temps.
burpod
teh stallionz!!1
- Joined
- Nov 27, 2004
- Location
- cape cod, ma
- TDI
- 82 rabbit vnt ahu, 98 jetta vnt ahu, 05 parts car, 88 scirocco.. :/
whats probably happening is.. timing is going advanced, target boost is being reduced, and you're getting constant overboost deviation and sending it into limp mode is my guess. the extra advance will create more boost combined with target being reduced and the pid controller is for some reason not doing enough of what it needs to do.... or so i suspect 
P2B
Top Post Dawg
That's limp mode due to over or under boost, unlikely to be caused by a faulty N75 in my experience.
I have seen cold weather limp mode caused by moisture in the pressure line from the N75 to the wastegate several times. It only takes a couple of drops, which have no effect until they freeze and then the wastegate doesn't open.
Please explain what are 011-001-004 ? I have Vagcom but have not logged any data , please explain the process. Thank You
burpod
teh stallionz!!1
- Joined
- Nov 27, 2004
- Location
- cape cod, ma
- TDI
- 82 rabbit vnt ahu, 98 jetta vnt ahu, 05 parts car, 88 scirocco.. :/
standard measuring blocks - 011 is boost, 001 is fuel, 004 is timing; would be worth it to take the 3 min it takes to setup a log and just log your trip when you think it might happen. it certainly could be something physical with the n75, but always good to investigate with log data to see what's actually going on with the numbers...
all about logging here
all about logging here
GTiTDi
TDIClub Enthusiast, Macht Schnell! Vendor , w/Busi
- Joined
- Oct 18, 2010
- TDI
- '91 GTI CJAA swap,'02 Jetta wagon ALH swap, '03 GTI 1.8T rally car, '03 Sprinter 3500
1Z/AHU turbo waste gate actuators often times fill up with oil from CCV blow by oil/turbo leaking oil into intercooler piping. When it gets oil in it it will cause boost issues especially when colder as it will become more viscous/gummy. Just what I've seen in my experience.
oilhammer
Certified Volkswagen Nut & Vendor
That's why I think any of these older wastegated TDIs still on the road probably would benefit from a new set of braided hoses every so often. Timing belt time is a perfect opportunity, since you're right there anyway.
Thank You
Abacus
That helpful B4 guy
My green sedan was one of these, I’d go through an N75 once a year. Installing a new one always fixed the limp mode and I could find no other problems. I’d been all through the car searching for any reason, and it happened with no tune and multiple tunes, as well as timing belts. I just kept a spare in the car. The wagons and other B4’s I’ve worked on never had the same issue.
I have now found that if I stay in 4th gear the limp mode will not happen. going to Kenai today in 5th about every 9 min. it would go to limp , I noticed it didn't happen in town so I decided to try to stay in 4th gear on the way back and no limp mode.
wonneber
Top Post Dawg
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- Oct 12, 2011
- Location
- Monroe, NY, USA
- TDI
- 2014 Jetta Sportwagon,2003 Jetta 261K Sold but not forgotten
Are you buying a real Bosch N75 or local parts store parts.
I had funny results with the local parts store one I tried.
thechoochlyman
Vendor , w/Business number
I've tried three or four different units in succession and they all acted differently. I had a brand new Pierburg, a used one, and a couple of used OEM N75s. The one that held consistent boost the best was one of the old OEM valves. The rest would all "bounce" the boost really bad, it couldn't hold steady at one pressure without going up and down.