Bad N75 symptoms

[BLUEBEAST]

Im having a boost problem, about a few weeks ago i would boost 16 psi then I installed the VMR test pipe and it would spike at 18psi, then all of a sudden about a week later boost dropped back down to 16psi so I thought maybe I got used to the car and the computer adjusted to it. So just recently had the Revo stage 2 software installed and the car would not spike past 16psi so I did a boost leak test and there were no leaks, but the turbo doesnt spike as hard, could this be a malfunctioning N75?

[hoganalley]

strong possibility. What about your DV? More than likely it would be a diverter valve. When my N75 went bad I could still boost high, it just fluttered. Felt like the car was shuddering. There are a lot of symptoms when the DV and N75 go bad. Check the DV first. If it's ok, then probably the N75.

[BLUEBEAST]

ok yea im thinking that might be the problem cause the throttle response is much slower now and it sounds like air is leaking somewhere but theres no leaks

[Groove1797]

What are you boost settings at? Do you have an SPS? You seem to be boosting low for revo software.

[BLUEBEAST]

no i dont have a sps but the revo mechanic said it said the ecu is asking for 21psi but it's not getting there and building boost slowly

[ScaryGary]

I had an n75 go bad and was spiking/holding 16/15. It also caused this weird honking noise that would eventually trip limp mode when cruising.

The n75 was the J model that I swapped in for the stock one. I tried putting the stocker back in and only boosted 10-11lbs.

I did the initial swap in the rain, and I think the water damaged the stock valve. I bought a new n75"F" (i think) and boost immediately spiked/held 22/20.

I think some adaptation has occured though and I am regularly seeing 20/18.5.

It's an expensive part, but it's very plausible that it's your problem.

[Groove1797]

no i dont have a sps but the revo mechanic said it said the ecu is asking for 21psi but it's not getting there and building boost slowly

You an I have the same problem.... exactly! I believe it is my n75 but I have not had time to fix it.

[BLUEBEAST]

yea I wanted to buy one from the dealership but they were like it's $116 and once you plug it in you cant return it so I wanted to make sure its the right part before I waste money and get stuck with it, its also making some honking noise too everytime i let off the gas almost sounds like a slight backfire

[Groove1797]

See if you have someone local with another n75. The only issue, if you break theirs.

[CO AVANT]

you haven't fixed that yet you lazy fvcker!

[BLUEBEAST]

lol yea one day I'll get around to it I been real lazy lately

[CO AVANT]

lol sorry I was talking to Groove1797(Tyler). He came up over a month ago and we figured this problem out after also finding and fixing a boost leak. I can't rag on you just yet BLUEBEAST Hope you get her figured out.

[Groove1797]

No! I was going to this past weekend but I cleaned the shit out of the car.... then it got watered by a malfunctioning sprinkler system. I know, lame excuse. Also, the right side of my car settled more so the heights don't vary as much. It's on the to do list this weekend.

P.S. those filters I ordered do not fit (wrong pt #). Sent them back on thursday last week

[CO AVANT]

I was wondering about those as I had to clean my oiled one before I dyno'd last weekend

[initiala4]

Just use vagcom and log block 115. Find an empty road and do a 3rd gear pull from 2500rpm alll the way till redline. Then from that data, find the differences between request and recieved.

[BLUEBEAST]

ok just to update this thread I took the car to the shop and the did some 3rd gear pulls and it showed that the car was asking for 21psi but was only making 16, and the actual boost curves were following what was requested but just at a lower point. So I thought it was the N75 and replaced it with a N75F valve and still the same problem and occasionaly if I play with the gas I can get the car to boost up to 19psi in 3rd gear, is there anything else i could check for?

[CO AVANT]

What DV are you running?

[Mark]

When my N75 went bad I could still boost high, it just fluttered.

my exact problem right now, fluttering at WOT and full boost. boost gauge goes from 22-20-22-20-22-20 . . . car surges with it.

[b6a41.8tbagg]

im guessing thats my problem aswell i spike at 12 and it drops down to 5 and dosent seem to wanna pick back up and my dv isnt loud anymore,not sure which version of the n75 to get and dont wanna put my ride in limp mode again any suggestions ive got giac stg1 apr tip and forge 007 dv

[A4SoftWalker]

First ur dv wont be loud anymore bcs u are not building as much psi as b4.

Second version F is the correct N75 to get.

Third have u checked all of ur vacuum lines? Replace any and EVERY stock manufacturer hose clamp u can see with a screw down type from an autoparts store.

I'm coming up with a write-up but I dont get paid for this stuff. I was stuck at 16 psi and no one could diagnose my car. Not APR, not Streekwerke, not 034.

See diagrams below:

10 clamps replaced here



Look at this rats nest of possible clamp leaks under the intake manifold:



Same 10 clamps in this pic



HAVE FUN wrenching

[diagnosticator]

The stock or upgraded diaphragm type DV are best and will provide the best operation when installed in the reversed from OE orientaion. That is with the bottom center port connected to the compressor discharge/boost pressure plumbing, and the side port connected to the turbo intake hose.

[SEATONE]

I recently found a boost leak and fixed it but the car continues to flutter. at times really bad and the car doesnt really have any power, but when I play with the pedal it kinda starts running ok and quickly back to missing. AAAHHHHHHH. I cant figure this shizzz out

[SEATONE]

Update on my issue. I had a few more leaks than I thought. I fixed them all and now my car runs like an animal LMAO. Its amazing what a couple vaccum/boost leaks can make your car feel like. Thanks guys for all the smarts posted.