No Boost Help Please!!!!!!!

[AudiA4Turbo22]

I drove today and everything seemed fine i drove 4 miles today and on the last 2, my turbo builds 10 pounds of boost and then dumps it back to zero. What the hell???? it doesn't sound like there are any leaks, no dentist drill noises nothing, and no CEL PLEASE HELP!

[AudiA4Turbo22]

please help.

[AudiA4Turbo22]

no one cares about me anymore??

[SlappyB6]

I'm definitely no expert, but it sounds like a vacuum pressure loss somewhere. My first stop would be to double-check for leaks.

[AudiA4Turbo22]

thing is it boosted fine, then all the sudden, it boosts and then the turbo kinda turns off.

[kwimberly]

I'm bone stock, and mine does the same thing. Thought it was normal. lol Get to 10 after pulling hard, then it drops.

[AudiA4Turbo22]

^^i'm not bone stock and it is suppossed to boost 21 PSI, it turns off. if i climb a hill it is boost no boost boost no boost....

[widgget]

i'm not expert here but if your boost is dropping it could be due to the waste gate opening, this would be caused by the N75 being stuck closed and as soon as you build up enough pressure to overcome the spring in the actuator then the waste gate is getting thrown open and you loose your boost.

Again, no expect but that is where i would look, i've replaced two N75 valves so far.

[demea]

Whats the Mercedes Benz dealer say ?
Sounds like a nice vacuum leak. Is your car real loud upon a cold start?
DV shot maybe?

[widgget]

^^i'm not bone stock and it is suppossed to boost 21 PSI, it turns off. if i climb a hill it is boost no boost boost no boost....

yeah, sounds like the waste gate is opening once it gets to a certain boost level, the GTRS actuator is set for 14psi i think (ie: 14psi to overcome the spring an open the waste gate) it might be part open before then though, i'm not sure.

[b6quattro]

What were the rpms when it fell off?

[kwimberly]

^^i'm not bone stock and it is suppossed to boost 21 PSI, it turns off. if i climb a hill it is boost no boost boost no boost....

at least my bump got you some activity!

[skizsam]

Try this:

http://www.a4mods.com/#index.php?pag...boostleak.html

[AudiA4Turbo22]

it's not a boost leak, it makes no obseen noises and isn't loud, thanx kwimberly, haha i just changed my N75 about 6 months ago, i guess i should try unpluging it and see where i get.

[A4Dit]

My car was constantly going into limp mode after installedy GTRS before i hd it programmed. It sounds exsctly like what you are describing. I also never had a cel during it.

[MultiAudis]

sounds like the wastegate to me

[aaaudiprotein]

You make boost, but it doesnt hold it, so i think either westagate or your diverter. Make sure it is connected good.

[AudiA4Turbo22]

My car was constantly going into limp mode after installedy GTRS before i hd it programmed. It sounds exsctly like what you are describing. I also never had a cel during it.

exactly, i'm still running the K03, it boosts then dumps all the pressure.

[AudiA4Turbo22]

sounds like the wastegate to me

exactly what i'm thinking, how can i fix this?

[pondside36]

What kind of DV are you using Kirk?

[AudiA4Turbo22]

^^2 month old 710N

[pondside36]

I would test that first being the easier route.. and if failed upgrade to a Forge or other piston type. Diaphram anything is inherantly prone to failure...

[AudiA4Turbo22]

^^i mean it is holding boost fine up to 10 pounds then just dumps it to zero for no reason. the DV is very strong still i had one on here for awhile before i changed just for the heck of it.

[pondside36]

It is strange.. but isn't the KO3 internally wastegated? Checking the DV, checking for boost leaks and what would be first to eliminate the easy stuff before you start tairing into the turbo stuff... just my .02

[nihil]

I had a similar problem last week, except my boost was falling off gradually rather than a sudden cut out (but then, I'm stg1/k03). There were two of those braided sheath vacuum lines that had gone to shit, IM to DV, and IM to <something mounted under IM>. Replaced both lines and it was good to go.

[AudiA4Turbo22]

All Vac Lines And Check Valves Are New. This Sux Up The Rear.

[widgget]

i've got money on the N75 being bad.

it makes even more sense that your falling off at about 10psi if you have a K03 still since the spring pressure is going to be less then the 14psi on the GTRS actuator.

Every time you get to 10psi you have enough pressure to over come the spring in the actuator and it releases the pressure, as soon as the pressure is released the waste gate is closed by the spring in the actuator and then you build up again until you get enough to reactivate the actuator. This is what is giving you the "boost, loose all boost, boost, loose all boost, ect, ect...."

If you had a piston type DV then i might question that, but a diaphragm DV is not going to build up till 10psi and then dump it all at once if it has a tear in it (it would just leak steadily) what you are seeing is what you would expect from a piston DV that has a bad line going to the top of it to hold it closed or if the spring in the DV wasn't providing enough resistance. i wouldn't expect this to be the issue so i wouldn't spend to much time screwing around with the DV, although a nice piston DV woudl be a good idea before you install the GTRS.

[RLB6]

VAG-COM. Check the duty cycle of the N75 valve. Second thing to check is the DV. Third thing to check is vacuum lines.

[AudiA4Turbo22]

^^u rule man(Widdget), i hope it is the N75, i'll check tonight ad it is an easy fix, i remember, when i was installing the new N75 when i blew through one hole it kinda leaked, maybe it was the problem, does the dealer have warranty on these things?

[widgget]

Don't know about a warranty on part from the dealer, i got my first N75H (H is the "race" version, just holds boost longer) valve from ecs tuning and the second i picked up here in the classified. but yea, mine was leaking like you just mentioned so i replaced and and it's much better now.

[pondside36]

NIce explanation Widgget, that makes perfect sense... Good luck and let us know what was the issue..

[widgget]

thanks guys, just trying to spread what knowledge i picked up from everyone else here. I try to explain whats going on (or at least how i understand it to work), personally i want to know why it's not working not just what to replace when something isn't working right.

RLB6 had a great idea if you have vagcom, although i am not sure if the duty cycle will still register correctly if it's stuck since the power to the solenoid will still be present. does anyone have input/comments on this?

let us know what you find Kirk.

[AudiA4Turbo22]

^^u got rep

[utripn]

get a new N75 valve and call it a day, then check your diverter valve and move on. It happened to me and it was the N75 valve, go to 034 motorsports and get the race version. all done.. see it was not that bad :)

[AudiA4Turbo22]

Well guys luckily i had my old N75 in my garage and everything was fine, except i recently changed my 02 sensor and i shifted into reverse today and the car stalled, ran it real hard and tested and all is well.


Thanx WIDDGET!!!!!!!

[pondside36]

Nice...

[Papachristou]

1+ cars seem to over boost and go into limp mode with the race valve

[AudiA4Turbo22]

^^i'm using the C valve i think, came on 02's only i'm gonna raise hell at the dealership about their part.

[widgget]

Great to hear you got it resolved! how much longer until you get the new turbo in there?

1+ cars seem to over boost and go into limp mode with the race valve

Thats what i would expect and i'm not debating you, but from experience mine never did over boost using the N75H with APR S1+ or S2, and now i'm on Revo S3.
i'm sure it happens though.

[AudiA4Turbo22]

^^AS SOON AS I SELL MY WHEELS. Now there is a new problem, i shifted into reverse yesterday and my car turned off, today the car is bucking? if i leave a light it goes power...no gas...power...no gas....power, changed my O2 last week i hate this car with a passion.