Need a little help w/ my 2000 S4

[titleiststud]

Hey everybody, I'm new to the forum and been reading all the good posts trying to find some answers to my problems but haven't found them yet so I figured I would post them up and see what you have to say. About two weeks ago I had multiple cylinder misfires, so I changed the plugs and the misfires stopped. After I changed the plugs though, the car started acting weird. It seems to be lacking in power below 4000 rpm and it hesitates really bad and feels like its missing between 3000 and 4000 rpm. When it hesitates, it will stutter and then give a blowoff valve sound and then pick up power again, but still not as much as it should. Above 4000 rpm, it has normal power. I've Vaged it for codes and I keep getting 17965: Charge pressure control: positive deviation (overboost) and b1 s1 and b2 s2 o2 sensor codes. Well, I took over my diverters because i figured they could be going bad since i was hearing a blowoff sound. They checked out and held vaccuum very well. I then disconnected the n75 and drove around without it to see if i would still get the overboost code. I didn't get the overboost code or the 02 codes that time, but the car still hesitated, just not quite as bad. Still gave the blowoff sound also. I'm at a loss as to what could be wrong and I need some help! I also ran the output tests and it's giving me short to ground on a lot of things including cylinders 1-6 injectors, n75, n80, and n249. Let me know what you guys think. I've got some upgraded dahlback dv's on the way and possibly an n75 to see if that will fix it. Thanks in advance for the help.

[titleiststud]

Forgot to mention that I've logged my boost and it seems to run 200-300mbar below requested until i let off the gas and then it runs 200-300 over requested. I've also got an mtm chipped ecu, but can't drive with it in right now because when it overboosts, it throws the car into serious limp mode, makes it idle funny, and i can't get the car to rev over 1200 rpm once it goes into limp mode.

[YBLEGL]

Check for a booost leak first my car was acting the same way when my TBB ripped and that is the most comon thing to rip.

[titleiststud]

I have the stuff to make the pressure tester, I just haven't done it yet. Can't be a tbb tear bc I have a Bi-Pipe.

[Dowskeet]

What about an F-hose tear..? 2000's love that.

[titleiststud]

Would it really cause that big of a problem? It did sound like I had a boost leak from my f-hose a few weeks ago, but retightened the connections and cleaned the hose and it seemed fine after that. I was thinking my n75 was going, but now I have no clue.

[lrg8683]

yes.. F-hose.. and it's a BITCH to replace.. get a samco replacement.. i tried making the home depot replacement and i felt like it leaked.

[titleiststud]

If I replace the F-Hose, I'm definitely going to go ahead and get the entire silicone kit just to avoid having to mess with it so much in the future. Thanks for the help guys. Still looking for some more opinions.

[lrg8683]

most of the other hoses hold up fine actually.. just the throttle body boot and the F hose that are the pains.

[The_Jerbel]

Build the boost leak tester and do a pressure test. Then if nothing comes up, replace the N75.

[titleiststud]

Build the boost leak tester and do a pressure test. Then if nothing comes up, replace the N75.

Thanks for the advice! The pressure test is no.1 on the priority list right now. I'll update when I find something out.

[titleiststud]

Do you guys think that I could have a bad N249 that is causing the dv's to open and thats why i hear the blowoff noise? If thats the case, has anyone done the n249 bypass on an s4?

[titleiststud]

Need some help with vagcom. I logged block 118 out of curiosity to the see the duty cycle for the n75 valve. It stayed at 0% almost the whole time and only went to 10.2% when i was hard on the throttle. Is this normal? I'm searching for info, but can't seem to find any. Need some help with this guys.

[rms-s4]

if your getting o2 codes log the calc load percentage. if its beloew 80% your maf is bad if its above it its ok. how many miles on it?

[titleiststud]

120k on the maf as far as i know. I've only had the car for less than 1k so not sure if it was ever replaced. What block is calc load percent?

[titleiststud]

But still, the 0% is not good for the n75 is it?

[rms-s4]

shit i have a snap on modis not sure about the vag-com. just take it out and clean and see if it changes any bit. if there is a setting to display current data just start it and look in there

[The_Jerbel]

Is your car stock or chipped? If stock, then that sounds about right. If chipped, then something is definitely wrong.

[The_Jerbel]

Do you guys think that I could have a bad N249 that is causing the dv's to open and thats why i hear the blowoff noise? If thats the case, has anyone done the n249 bypass on an s4?

yes and yes

[titleiststud]

Car is stock, but I have a chip waiting to go in when I get the problems solved. The car is much more driveable with the stock chip in it for the moment. On bypassing the n249, does anyone have a diy done or could give me a rundown on how to do it with a few pictures maybe. That would be greatly appreciated.

[titleiststud]

And this is going to sound like total noob question, but how do you take off the MAF? It looks like its clipped in, but I can't seem to get it unclipped. I know there are two "screws" holding it down which I would have to buy a tool to fit since it has the raised ball in the middle.

[The_Jerbel]

Sounds like normal WGDC for stock.
Here's a pic with arrows showing you what to do. Do everything you see in the arrows. Plug both ends of the line it says to plug there.

[The_Jerbel]

And this is going to sound like total noob question, but how do you take off the MAF? It looks like its clipped in, but I can't seem to get it unclipped. I know there are two "screws" holding it down which I would have to buy a tool to fit since it has the raised ball in the middle.

Do you want to take off the MAF housing or the sensor itself?

[titleiststud]

I just need to unplug the sensor and i know it's just clipped in but i can't get it unclipped for the life of me.

In the pic where you have the two hoses coming together, what fitting is in there? and for the other hose, just unplug it and plus the hose and the place I unplugged it? What bolt did you use to plug the end of the hose? and i guess I can pick up the other plug/cap at an auto parts store correct? Thanks for the pic, it is exactly what I had in mind when I asked for help.

Did you notice any difference in performance or feel of the car when you bypassed your n249?

[audiwop]

Like others have said, i would bank on your F-Hose being the culprit. Mine had a little tear in it and my car was doing the same thing as yours. I went with the samco and all has been fine since.

[The_Jerbel]

I just need to unplug the sensor and i know it's just clipped in but i can't get it unclipped for the life of me.

In the pic where you have the two hoses coming together, what fitting is in there? and for the other hose, just unplug it and plus the hose and the place I unplugged it? What bolt did you use to plug the end of the hose? and i guess I can pick up the other plug/cap at an auto parts store correct? Thanks for the pic, it is exactly what I had in mind when I asked for help.

Did you notice any difference in performance or feel of the car when you bypassed your n249?

Smoother onset of boost between shifts now without the N249. I just used a little coupler fitting from a hardware store going between the two hoses. Yeah just unplug the hose and cap it as well as the nipple that it came off of. Any vacuum cap will do. I just used a bolt that was a little smaller than the hose and wrapped it in electricians tape and pushed it in.

For the MAF, push the connector DOWN (into the senor), then pull the tab up and the connector should slide up.

[titleiststud]

Well I've eliminated possible problems with the n75 since the duty cycle seems ok, i bypassed the n249 and took it out for a spin tonight with not much improvement, and i logged the maf while i was out and it seemed normal. Looking more and more like a boost leak. It's so strange hearing the blowoff sound after I've been on it really hard. Always thought that that sound would mean a bad dv, but they checked out fine. If it's a boost leak, i still don't understand while I'm getting the overboost issue. strange.

[titleiststud]

Well I bought the zena racing silicone kit off ebay, so I'll be changing that. I also bought a manual boost controller that I'm going to run in parallel with my n75. I'll keep you guys updated.

[2fast4me]

I had the same problem w/ mine, put in the new dv's and samco kit and all is well. Im sure you will be fine

[titleiststud]

Just thought I would give everyone an update on my progress. I bought an MBC to run in parallel with my n75 to cut the boost spikes and while i was installing it, I somehow stumbled across my problem. Other than some crappy work from someone who had the car before me with some t valves, I also noticed a hose disconnected from my bi-pipe. Yep, that'll do it! I reconnected if after removing the head light to reach it and.....it runs like a champ. Installed the ecu w/ mtm chip and this thing is unbelievable now!