Hey guys, I have been roaming around the forums for about a month or two now and I think its time I come out of the woodworks. My name is Andrew im 20 and a student at The University of Texas in Austin majoring in Computer Science, this coming up fall I will be starting my junior year. I am fairly new to the Audi scene, I had a 93 Honda Accord for about 4 years till I decided its time to move on up. I purchased a 98.5 Audi A4 1.8T 5spd w/ 84k miles for a beyond killer deal. I have every maintinece record from day one of the car, it was serviced entirely at an Audi dealership and has had nothing but Mobil1 full syntetic oil (it was owned by a lawyer then a college professor). Obviously the car is entirly stock, but I plan on doing some minor modifications to the car nothing terribly exciting.

I am fairly proficient at using the search button, and I normally like to stay back and observe from a distance rather than giving my 2 cents, I doubt I have every had a post count above 10 if you get my drift. For some reason though I have the sudden urge to be part of something again like I was in high school, so why not my cars forum.

But onto the more important stuff, I received a vag com from a friend and have been tinkering around with it. I pulled the ECU codes the first night, didn’t see anything worth freaking out about. Cleared the codes and pulled them again a week later (today) and I got 1 code: 17956 – Boost Pressure Regulation Valve (N75): Open Circuit. Did some searching and I found mixed results. Here is the deal, I have a boost gauge and it shows about 7lbs of boost under load and I see it drop to about 5lbs around 4-5k RPM. I hear the turbo spool, and I deffinatly feel it. The problem is why is the ECU throwing this code? I cleared the codes tonight and will pull them again in the next day or so. If it needs to be replaced I plan on replacing it with the N75F, the most I plan on doing with the car is MAYBE getting it chipped and an exhaust. I hear so many different things about which version is better my head spins, and that if you plan on getting it chipped stay with the stock version because there are less problems (or so I hear). If I need to change the N75 I hear to change the DV while you are at it, I plan on replacing it with the 710N DV unless that’s a bad idea.

Here is my biggest problem though, I like details. Ive messed/read about the vag com more than ive driven the car. I understand my car is the pre-facelift, and ross-tech says “Use as a general guide for engines starting ABOUT 1999…” on their standardized block groups listing but pretty anything that I care to pull (ie: 032, 110-119) doesn’t exist on my car its just says “N/A” I wanted to check block 115 to see how my boost was, and now with the N75 ECU code I wanted to check the duty cycle of the valve to see if it was malfuntioning, but I cant. I cant seem to find a block listing for my car, unless its in the bently manual which I plan on buying soon. I figured “about 1999” would include my car, obviously that doesn’t seem the be the case unless I am doing something wrong.

I have some more clarifications but im still reading about them and do not want to pre-maturly ask, and this is already fairly long. I plan on doing a major tune up/some modifications this weekend already (trans and diff fluid, replacing my rear deck speakers, airbox mod??, tons more) so I wanted yalls input on what I should do about the N75 valve.

Obviously any input is greatly appreciated.
Andrew

 

I would assume that that means that your N75 is eithere going or dead. I know if the vac line is off the DV you will only get about 5-7lbs of boost. You should be able to check the N75 with a multimeter but im not too sure what kind of readings you should be getting. Hopefully someone will chime in with more info.

 

I would go through each channel and see what kind of info you can find. For instance, mabe the boost readout is not on channel 115 on your car.

The DV does not need to be replaced unless it is broken or you get a chip.

Check the electrical connection to the N75. A new N75 will run you abou $100.

I beleive the cars became DBW for 99.5 and newer models. Your car is DBC.

welcome

 

Late last night I did just that, I went through every block 001-150 and there are not many blocks that contained anything. Looking at the chart on ross-tech I figured I was looking for anything that contained “mbar” I found one (block 113) that read Abs. Pres. – 1003.2 mbar and it never changed even when I drove it around the block. So I think that the vast amount of information on vag com does not pertain to my car, which is a big downer. Is there anything that pertains more towards my car elsewhere? Because the more I read it looks like a majority of the information is for 99.5+ A4’s
As for the N75 I have a VW dealership not 5 mins away from me that want 105 for the part. I found a post that has the resistance ratings for a variety of the sensors and I plan on checking that once I start my work this weekend. Are the resistance ratings a good gauge to tell if my sensor is bad?

 

well i got done with alot tonight, i was very surprised and relieved that the wire had broken off in the connector. i checked the resistance and it was well within the spec (29ohm).

i ended up doing alot today on my car, pretty much worked on it all day. i extended my FOB antenna but i dont think it helped much at all to be honest, hacked in a aux in for my MP3 player without having to buy an adapter, did the airbox mod to an extent didnt want to go too crazy with it.

i do have one question though, i absolutally cannot hear my DV when i let off the gas. i know i am not suppose to hear an audiable "pssh" frankly i dont care if i do but i want my car to be in tip top shape so i dont have to deal with much when im at school. am i suppose to hear anything stock?

 

you wont hear much with stock boost

 

how did you hack you aux for a mp3 what radio do you have

 

i think for anyone to do this mod you have to already have a cd changer, because otherwise there is no way for you to fake the data easily so the radio thinks you are playing a cd. i have a cd changer and i just used a 2 pole switch to switch the left and right channels from the cd changer to my mp3 player. in my case the diagram was on top of the radio for the left and right inputs (pins 19 & 20 if i remember correctly) i took some pictures while i was doing it. if more people are interested i can throw something together. it works great for what i need, and it cost me $5 in parts.