Hey everyone, new to the site but no noob to cars. I have had my fair share of cars and from WRX's to classic muscle, but this car has me stumped. I bought a 2000 quattro 1.8t back in november, it lacked a little power when i bought it but the turbo would still spoool and build a little boost. About 3 months ago While i was driving i lost all boost suddenly, I parked it for no more than 5 minutes, came back to drive it and the boost was back, but it did the same thing and about a mile or so down the road it lost all boost again. There were no boost leaks so i replaced the DV with the upgraded one and the vacuum line from the DV to the intake (can someone tell me what the T is that the hose plugs into?) and the good news I had tons more boost/power when it was there but it still cuts out a mile or so down the road. I tested my N75 at 30.9 ohms (im told 25-35 is good) and even hooked up 15 psi of air directly to the wastegate and it seems to be working fine. Im stumped, something is makeing my wastegate open and stay open, but everything tests out ok. I Have had 2 CELs come and go randomly, but i dont think they are related to my boost issue because they have not been on for about a week, and they come and go seperately, never together. They are a P1114 and P0420 which make me think my cat and O2s need replaced. Could those be related? Im leaning towards bad turbo internals, or a bad N75 even though it ohmed out ok. Im not sure what consists of audis limp mode but most cars Ive seen the CEL or some other light comes on, and nothing happens when the boost goes, it just goes. Any help is appreciated. so for writing the novel...

 

I am having the same exact problem it sounds like. I thought it might be the N75 as well so I ran it w/out the vacuum line hooked up. no change. If my thinkin is correct the wastegate is normally closed and the actuator opens it and bleeds pressure right? I was thinking maybe the wastegate has some crud on it and isn't quite closing possibly. Unlike you though I lost my power and never saw it again. Good luck, I'll let you know if I find anything.

 

Yes your correct, the wastegate stays closed until max boost is acheived and it opens accordingly to control exhaust flow to the turbine. since everything i tested checked out, I found this awesome write up after some serious searching. I beleive my N249 is bad, it electronicaly controls the DV, so im going to bypass it and hook my DV straight to manifold pressure and hopefully my problem is resolved, if not looks like im saving up for my complete stroker kit and new turbo.
heres the article
*DIY* - B5 1.8T Vacuum/Check Valve/SAI/PCV - Delete & Simplification

 

I did the N249 delete and all is happy, have my boost back, its a more clean and crisp delivery and it pulls all the way through rpms

 

Awesome, I'm glad to hear you fixed it. I'll have to see if I can do the same. Thanks for the link.

 

well i guess it was only time, i lost all boost again. Im almost certain its my N75 and its sticking alowing my dv to bypass all the boost, i can hear my turbo spooling but theres no power. If this wont fix it ill have to replace my turbo...

 

The N75 controls the wastegate, you mean the wastegate isn't being properly controlled, right?

 

I just looked at mine too and remembered I did the SAI and n249 delete a long time ago. I was thinkin of installing an MBC. But if you disconnect the n75 it shouldn't bleed boost at all right? Therefore it should give max boost? To me if it was a wastegate problem it would be that the wastegate wont close completely and bleeds boost through the entire band. I dont know I'm no expert here. Another guy suggested to check and make sure the wastegate actuator rod is connected to the wastegate. keep us posted on your progress.

 

My bad, I meant the wastegate not dv. My wastegate is working ok when car is shut off, i manually hooked air pressure to it and it goes back and forth no problem, not loose or sticking either. Heres the scenarios I have thought of
1) although my N75 tests out ok, somthing is causing it to stick and keeping my wastegate open patially or fully, whether it be the computer making it activate, or its sticking internally. Remember, whatever ***** up resets when i turn the car off and let it sit a few minutes. And i read a forum where a guys N75 tested ok at room temp but tested out of spec and would malfunction as it heated up.
2) My MAP is bad, causing the computer to read a wrong (overboost) situation and causing my N75 to activate. Does anyone know what the MAP should test at, or what the reading shoud be on a scanner while driving?
3) my wastegate appears to be functioning but could have an internal/actuator malfunction

Heres what im thinking, when I can afford the 45$ for a new N75 ill try that. In the meantime, can't i just hook the wastegate directly to the intake and plug the port on the N75? Or do audis HAVE to control boost with the N75 or MBC? I know some cars have an intenal spring to control boost, All the N75 does is provide a vacuum source to the wastegate when the car is boosting, alowing the computer to shut off boost whenever it deems necessary even under WOT. I drove it for about 6 miles just a little bit ago and the boost never left. This is really starting to get to me...

 

My WG actuator was bad and not holding the WG closed completely. Don't know if it could be the same for you because you had boost back for a minute. Just thought I'd let you know what fixed mine. Good Luck