Need help asap!!! S4 overboosting!

[Allaidback]

I have an audi b5 s4 and was driving on the interstate and check engine light came on...I'm getting the code checked in the morning but one thing I noticed is when I accelerate at wot the boost gauge spikes at 25psi and stays at 25psi and acts light a rev limiter and the whole car starts to shake and acts like it bogging and cutting fuel. I have awe's stage 3 kit with fueling on the car. What could be causing the overboosting? What should I check. Thanks guys for the help. This is my first s4 so I am clueless. The car pulls hard till it spikes at 25psi and then this happens.

[exorcet]

either boost leak or bad N75 valve would be my first guess. i would stay out of boost until you diagnose what is going on, as it sounds like you might be spiking over 25 lbs.

[RolledMySTi]

either boost leak or bad N75 valve would be my first guess. i would stay out of boost until you diagnose what is going on, as it sounds like you might be spiking over 25 lbs.

+1

[exorcet]

also, it try unplugging your N75 (sensor right in front of the MAF housing/accordian hose.. brown square connector) -- this will allow you to test if you have a leak in the wastegate line, which can cause overboosting.

unplug the N75 (just the electric connector, not any hoses/tubing), and see if you only get 7-9 pounds of boost at WOT. If you do, your wastegates/lines are probably ok and you can rule that out. If you go higher.. you'll know that's where your leak is.

Here is where the N75 is, circled in red. This is also something AWE recommends replacing as preventative maintenance on any higher mileage stg3 cars.

/thanks to Cole for letting me steal this image of his engine from another thread without his permission. ;)

[Allaidback]

also, it try unplugging your N75 (sensor right in front of the MAF housing/accordian hose.. brown square connector) -- this will allow you to test if you have a leak in the wastegate line, which can cause overboosting.

unplug the N75 (just the electric connector, not any hoses/tubing), and see if you only get 7-9 pounds of boost at WOT. If you do, your wastegates/lines are probably ok and you can rule that out. If you go higher.. you'll know that's where your leak is.

Here is where the N75 is, circled in red. This is also something AWE recommends replacing as preventative maintenance on any higher mileage stg3 cars.

/thanks to Cole for letting me steal this image of his engine from another thread without his permission. ;)

So if my psi goes higher than 7-9 pounds then its my wastegates/lines? how would I replace those? and if I it stays within 7-9 pounds then what would be my problem? How would I tell if it is my N75 valve?

[The_Jerbel]

either boost leak or bad N75 valve would be my first guess. i would stay out of boost until you diagnose what is going on, as it sounds like you might be spiking over 25 lbs.

The only way it would be a boost leak is if it was a WG or a boost reference line that was leaking.

OP, you should log block 119 and 115 and post them here. Pressure test the line coming off the side of the N75 toward the driver's side of the car. Make sure it holds pressure. What exorcet is saying is that if you unplug the N75 it should throw you into limp mode and you should only boost to 7-9psi. If you do, then your WG lines and WG's are functioning properly, if not, then they may not be. The most fool-proof way of testing the N75 and its lines is to log it, and pressure test the lines, like I mentioned above.

[offroader1006]

I VAG'd the car and drove it this morning.

only has catalyst eff. codes.

its hitting WAY more than 25, as its going past 25 by at least 5psi on his AWE gauge.

maxed out the MAP sensor as well. working on uploading the 115 log i took.

N75 looks original, so i told him to get one monday, our dealership's closed on sat's.

BTW, his doesn't have the shiney blue, red, orange and yellow things or shiney cap pictured here:

could that be part of the problem?

[offroader1006]

[exorcet]

BTW, his doesn't have the shiney blue, red, orange and yellow things or shiney cap pictured here:


could that be part of the problem?

No, not part of the problem. What is the setup on this car - i'm assuming K04's... if not i think the K03's would be dead now.

Do you what software/hardware this car has? From all the information I'd say WG line or N75.

[johnkent1212]

You also may have coolant leaking into your oil...common problem when the seals leak.......if you taste the oil and it's at all sweet that's the problem....or one of them.

[The_Jerbel]

^^^?????

Anyways, offroader, I can't read that log you posted, try emailing it to me [email protected]

[Allaidback]

Ok...one of the hoses hooked into the N75 valve had come off! Replaced the hose and now car only boost to 15psi. Checked all hoses and tightened up everything. Unplugged the ecu and restarted the car...runs at 18psi and holds with no spiking??? Car was spiking before to 24psi, holding at 22psi and glides to 18-20psi. I ordered the a new n75 and vast mbc...you think this might fix the issue?

[exorcet]

Ok...one of the hoses hooked into the N75 valve had come off! Replaced the hose and now car only boost to 15psi. Checked all hoses and tightened up everything. Unplugged the ecu and restarted the car...runs at 18psi and holds with no spiking??? Car was spiking before to 24psi, holding at 22psi and glides to 18-20psi. I ordered the a new n75 and vast mbc...you think this might fix the issue?

yeah, there is a good chance it will, i think. but you should also do a pressure test to make sure you don't have any other leaks.

[Allaidback]

It's funny...this is my first turbo car and you can really tell the difference in just 2psi!!! I never even thought that could make such a huge difference in acceleration.

[AudiSportB5S4]

if you taste the oil and it's at all sweet that's the problem....or one of them.

yeah i mean if you put it on your steak and you die that means you're good to go. lol

[johnkent1212]

1 psi = roughly 15 horses.

[johnkent1212]

yeah i mean if you put it on your steak and you die that means you're good to go. lol

I didn't say drink the stuff...just a little taste. I kinda set myself up for that one...haha

[offroader1006]

one place i didnt check visually was the "F" hose. definitely a likely spot for a leak.

andrew, if you search "F" hose in the B5 S4 forum you should find some pics and a description. jake has an upgraded "F" hose, if you want i am sure we could put one on yours sunday.

[exorcet]

1 psi = roughly 15 horses.

no wonder when i had my MBC set to 15psi it only felt like i had 225hp.

[S4 in_lowplaces]

some of these replies are funny. haaa

[johnkent1212]

some of these replies are funny. haaa

You're funny.