Hey fellas,
Im a noob to the audi world, however I have been working with turbocharged cars for years and I am working on my friends 2002 A4 to solve a particular boost leak. After briefly reading some of the stickies, I learned that air is measured through a MAF sensor on these cars so a boost leak could mean much more then a bad vacuum line or popped off coupler. Forgive me if I get any of this wrong but the car is modded with a K04 turbine and a stage 4 ecu upgrade with DV (not BOV) and catback exhaust. I tee-ed a boost guage into the intake manifold and took the car out for a few freeway runs to see the boost pattern, here they are.

1st gear 11psi to redline.
2nd gear 11psi drops to 7psi redline
3rd gear 0psi
4th gear 0psi
5th gear 13psi

The only time I can get 3rd and 4th to boost is when downshifting from a higher gear and getting on throttle. I can get 13psi on both gears doing this but nothing upshifting. My buddy who owns the car doesnt know d*ck (no boost guage with those mods wtf?) about the car so it makes it harder to troubleshoot not knowing what the thing is set to boost at.

I apologize in advance if this is an obvious fix that i didnt read in the FAQs, I would really like some help pinpointing the leak (if it is a leak) without having to tear things down since I am a noob to this car.

Thanks for reading, much appreciated.

 

there's a thread a few down called tennis ball method. if you have an air compressor you will find the boost leak really eassily.

 

This sounds beyond just a boost leak. Also, if you didn't know, boost is actually controlled electronically by a solenoid (N75 valve) via the ECU. With such erract boost amongst the gears I would start with the ECU programming in corelation with the N75 valve and go from there.

 

Who is the chip manufacturer?? Stage 4??? Never heard of that for k04. Are there any noises to go with this lack of boost? Like hisssing?? Check the turbo outlet hose on the bottom of the turbo. Is he using a manual boost controller or n75? If n75 is it stock or different version?? But again, i dont know about this stage 4 stuff for the k04 so it may be a chip/programing conflict.. Like, is it APR, GIAC, Revo??

 

Thats what I thought originally, something more then just a vacuum line because the ECU controls boost (through the N75) by getting air readings from the MAF right? He says its chipped "stage 4" whatever that means. What kind of boost should he be getting with this upgrade? I think I need to speak to the guy who put this together in the first place.

smokeU - thanks for the direction, thats an interesting way to check for leaks : )

 

Im trying to get more info on the chip as we speak. As far as noises, I cant hear a real audible swoosh/hiss or venting of boost. Turbo outlet looks good visually. There is no aftermarket boost control so I assume its actuated through the n75 you speak of. I will try and find out if the n75 valve has been upgraded? Sorry for the lack of info, hopefully more coming soon. Thanks for the reply.

 

Yeah find out who makes the chip. If he is using anything other than the stock n75 valve he will have problems with it because the k04 and "performance" n75's dont mix well.

 

Take it to autozone and get it scanned for free. Post the codes here.

Did he upgrade the DV? If it's still running the stock DV (it's plastic), the rubber diaphram may have torn.

 

I would think that if the DV is torn..it wouldn't build boost at all and if it was not totally damaged, then it would build boost, weak boost, but in all gears though. This car is having problems to where its not building boost in some gears, but others, and only on upshifts. Very weird but not out of reach to resolve.

 

OK he says the ECU is GIAC "x chip" or something of that matter. Says its the best chip they make? Anyway the DV is fine, its been upgraded to the hyperboost one from what im told. I have had a similar problem with my RX7 in the past and it turned out to be a slit in a vacuum line. It would push boost out the slit upshifting but once the motor decelerates and creates vacuum, it would seal the slit thus giving back some boost in 3rd and 4th just like his car is doing now. The difference is boost is controlled via MAP sensor and TCS (turbo control solinoids) not ECU like the Audi. Hmmm...