How do i diagnose bad n75 valve??

[wesleyfbm]

so im thinking i have a faulty n75 valve but i dont know for sure and def dont wanna blow money and not have that be the problem.

im just having horribly consitancy with my boost. could be spiking 16 one day then 7 the next.

no CEL either.

how should i go abouts finding the problem. thanks guys

[lifwanian]

Running through similar problems. Could be anything really... Anywhere from plugs, to coils, to air temp, to MAF, to ICM, to boost leak, to N75, etc...

Any codes?

[as4driver]

I removed my n75 on my a4 due to a similar situation. I replaced it with a MBC set at 18 psi.

[FrancoTheTanko]

you can look at the duty cycle percentage in blocks 114 and or 118. That's all I know, not sure what you should be seeing to diagnose a bad valve though.

[danphines]

if your looking at the valve there are 3 vacuum hoses going to it. unplug the one on the top and test drive it. DO NOT GO WOT! make sure you keep an eye on the boost cause your wastegate will not open

[Neelym90]

Had a very similar problem, Danphines diagnosed it as a bad DV(mine was stock, trying to hold 21psi)...we put on his splitter and it held. Ordered my splitter today will confirm that was the problem when I recieve it.

[wesleyfbm]

so if i unplug the top vac line to the valve this cuts off the waste gate? and how does that effect the car?

[Jc61990]

so if i unplug the top vac line to the valve this cuts off the waste gate? and how does that effect the car?

should be getting little to no boost i think

[dcampana]

that will not allow the wg to open and cause boost to increase. as danphines said, watch your boost and dont go WOT....

this is a way to fidnd out if the n75 is faulty, or if you knwo someone local that you can swap them with to see is another way.

[wesleyfbm]

alright thanks guys ill have to give that a try.

if it is the problem whats a better solution, new 034 n75 race or a manual boost controller?

[danphines]

since your an 01 i dont think a race will work for you its just gonna throw you in limp mode. to be safe i would just buy another stock n75 if you conclude thats what the problem is because they are sub $100 level. mbc is just going to have a jerky as hell ride its going to shoot into boost and not be smooth at all thats why you dont run a mbc by itself.

[wesleyfbm]

wait so what does it prove if i remove the top vac line im confused now?..maybe just tired.

so will i see more boost or no boost on my gauge??

and if i get more boost then that means the n75 is faulty?

[wesleyfbm]

??

[walky_talky20]

By removing the vacuum line from the N75 to the wastegate acuator you are basically disabling the wastegate actuator - the wastegate will never open. The boost will be higher as it is no longer being limited. If you go WOT you run the risk of overboosting and running lean or detonating.

If you remove the line and are able to achieve the correct amount of boost (whilst being careful not to overboost) then you may have a bad N75. If you remove the line and it runs the same then you have a wastegate problem, turbo problem, or a large boost leak.

Even if you don't have a CEL, check the codes first before you do anything else. Not all codes trigger a CEL. Could be soft limp mode or something.

[wesleyfbm]

thanks walky talky that was a big help

[wesleyfbm]

so took the waste gate line off the n75 and was up to 17psi and still rising. so im guessing i do have a bad n75 valve.

so question is....should i find a used one cheap or just be safe and get a new one??

thanks guys

[walky_talky20]

It is probably best to get a new one as these things do wear out over time. Although I'm a cheapskate and would probably try to track down a used one myself, haha.

Have you checked to make sure you have no codes (not just a CEL, you have to scan for codes). The other possibility besides a bad N75 is the computer is actually limiting boost - called soft limp mode - based on any number of things (boost pressure too high or too low, or weird maf readings, etc). On these cars you really have to check for codes first before you do anything else. Good Luck.

[KBB5]

yo wesley what sofware you running and how many miles on the car?

[wesleyfbm]

i have apr and at 91k

and havent checked codes on vagcom but obd doesnt read anything. it has a new maf too.

[walky_talky20]

Definitely get a vag-com if you don't have one already. It is invaluable when trying to diagnose these cars. Also you can do a few cool tricks with it.

http://cgi.ebay.com/ebaymotors/Vag-C...motiveQ5fTools

The cables can be had for less than $15 shipped and work with the free version of the Ross-tech software. I can't imagine owning my [high miles] Audi without it.

[KBB5]

im guessing it could be secondary O2 sensor

[wesleyfbm]

okay so heres a little update.

i installed another n75 that i bought for $30 from some random on vortex....and i have same results. nothing over 12psi

i did take off the vacuum to the wastegate and got high boost(17 and rising)...so what is my problem? im agrivated.

the new-used n75 junk aswell?

also are all 1.8t volkswagon and audi n75 valves the same?

[terraflata]

BTW Just a little suggestion. If you completely remove your N75 for testing purposes. Accelerate in a higher gear when testing (3-4). Bad things can happen flying through RPM's with nothing to control boost pressures.

Terraflata

[wesleyfbm]

yah i knew this(previous posts) thats why i stopped at 17psi..didnt want to overspool. thanks tho

[wesleyfbm]

anything??

[walky_talky20]

If it is not the N75, then it is the signals to the N75. Check the vacuum lines going to it and make sure they are OK and connected properly. Especially make sure the line to airbox (atmospheric input) flows freely. The electrical signal that controls the N75 comes from the ECU. Do you have any codes?

[wesleyfbm]

no codes and when i unpluged the electrical line i went from 12psi to 5psi.

i heard maybe wastegate actuator??

[walky_talky20]

When you unplug the electrical side of the N75 it goes open and sends full boost pressure to the wastegate actuator. Basically the boost control is then run completely by the wastegate spring which opens somewhere around 3-5 psi.

If you've got an '01 your car has a charge air pressure sensor so the ecu can monitor the boost pressure. Use vag-com to log actual boost vs. requested boost. Also compare these numbers with what you see on your boost guage.

I think if the ecu is actually requesting 16+ psi, and your getting less than 10, you should have a code. Perhaps not a CEL, but at least a code.

[wesleyfbm]

well what pops up when even tho i dont have CEL is lean fuel code...idk its been like that pretty much since i bought the car.

[wesleyfbm]

and yes it is an 01

[walky_talky20]

I'm not exactly sure which things in particular can cause soft limp mode, but I think the ECU could definetly be limiting boost due to a lean condition. Try logging actual vs. requested boost. As long as those values line up pretty closely, then everything in the boost control system is working fine (wastegate, N75, actuator, etc). The only problem would be why the ECU is not requesting full boost. Have you logged the MAF lately? A faulty or dirty MAF is a common cause for lean issues.

[wesleyfbm]

i wish i owned a vag com. its a fairly new maf sensor. want to say maybe march i purchased it.

[walky_talky20]

Well, I'd suggest fixing known issues first. If you know the car is throwing a lean code, fix that first before trying to fix other stuff. I wouldn't want to go to full boost anyway if I knew my car was running lean. My suggestion is to spend $15 and get a vag-com cable. You are really flying blind without it.

[wesleyfbm]

thanks for all the help man. appreciate it.

[wesleyfbm]

do the ebay vag com's really work good and how hard is it to use?? ive never really looked into it before.

[walky_talky20]

Yep, mine works great. You get the vag-com shareware (free) edition software from ross-tech's website, version 409.1. When looking for cables on ebay, find one that says "409.1" to make sure it works with the newest possible free version.

It is a bit limited, however. You can read out all the Trouble Codes, but it doesn't "decode" all of them for you. A quick search on Audizine or google usually takes care of that. Also you can only access measuring blocks up to 025, the rest are blocked. In your case you could look at and Log the MAF values, but not the Boost pressure. You can unlock it for $99, but if you are going to buy it, it is best to get an official cable and the newer software. Their newest software versions only work with their official cables AFAIK. That would be $229 and up depending on which cable you get. The more expensive cables work with newer (2003+) cars.

Here is a great thread to check out. Sections 1 & 2 discuss purchase, installation, and software stuff pertaining to the Ebay cables.
http://www.audizine.com/forum/showthread.php?t=158766

[wesleyfbm]

yah i had checked that link out earlier today. i just dont have the money for anything crazy expensive and dont want to buy a cheap one and not have it work.

[bob12312357]

Running through similar problems. Could be anything really... Anywhere from plugs, to coils, to air temp, to MAF, to ICM, to boost leak, to N75, etc...

Any codes?

ICM=In coil packs as his car is an 01

[HumbleTurbo]

By removing the vacuum line from the N75 to the wastegate acuator you are basically disabling the wastegate actuator - the wastegate will never open. The boost will be higher as it is no longer being limited. If you go WOT you run the risk of overboosting and running lean or detonating.

If you remove the line and are able to achieve the correct amount of boost (whilst being careful not to overboost) then you may have a bad N75. If you remove the line and it runs the same then you have a wastegate problem, turbo problem, or a large boost leak.

Even if you don't have a CEL, check the codes first before you do anything else. Not all codes trigger a CEL. Could be soft limp mode or something.

Been a loong time since anyone has posted on this thread. This information just saved my ass though. I did exactly this test and discovered a bad n75, an issue I've been dealing with for waay too long. Thanks again

[walky_talky20]

Long enough I didn't even recognize it was my own quote. ;) You're very welcome. Glad it was helpful.


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