The Project Pad

The Audi has been down on boost lately. I figured I'd see whats going on with the car today, its been running spring pressure (6psi) for awhile now with no codes in the ECU. Today I pulled the WG vac line and plugged it, hello 15 psi & fuel cut. I'm now convinced I need to fix my boost issue. I started with the N75, cleaned it out, and it clicked when I ran the output test on it, seemed to function properly. But still no boost. So I decided to see if I could read the duty cycle on the N75, 30% at 5k rpm, WOT. Hmm, why is the ECU limiting boost so low? I cleaned the MAF, made some difference. The car is now running just over spring pressure, maybe 7 or 8psi. I will check the N75 duty cycle again tomorrow with the clean MAF. Any insight on where to go from here would be welcome.

And some pics with a friends E36, from last week:

Small update. Found the MFTS connector full of coolant and disconnected it. After disconnecting the MFTS I immediately test drove the car and it did reach 11-12psi of boost. However the next day (MFTS still unplugged) the car started limiting boost to spring pressure again. I also think the thermostat is stuck open. I will replace the MFTS, thermostat, and knock sensors next weekend.

How did the connector get full of coolant? Weird. Good find though.

The MFTS was leaking into the rubber boot around the connector, the boot was filled to the point where the connector was almost completely submerged. I must have disturbed the sensor when I had the engine out, causing it to leak.

Nice to see someone else bringing an old avant back to life. Don't give up on it, there's only so much to break... Haha.

I'd go ahead and replace the N75 valve (MAC valve can be had for less than $40 and supposedly works with stock ECU, i'm on VEMS though) and if you can get a hold of a pressure testing or smoke testing setup do that. Or at least take a mightyvac to the ECU boost line.
Are you privy to sjmautotechnik? Invaluable resource.

Also any chance you could send me a higher res image of that window sticker? Never seen one for the 200 avant before

I'm kinda pissed at the car right now, it locked me out again yesterday. I had to punch the hatch lock to get in.

I have thoroughly checked the n75. I've read the duty cycle under boost on a test drive. I've Ohm'ed it out. I've run the ECU output test on it. And I have wired it to a switch that I can manually activate while under boost. I can't find a thing wrong with it, based on the duty cycle reading I got I believe the ECU is limiting boost for some reason.

Yes, sjm is the only reason I have made it this far with the diagnosis.

I'm not so sure that the stock turbo should need a whole lot more than 30% DC (for stock boost). Just something to consider. That could be totally wrong.

How did it lock you out? The keys were in the car?

Isn't the n75 DC the amount of time it would be closed?

The lock linkage inside the passenger door broke, drivers side has been broken for a while. I never had the key for the hatch.

The duty cycle is how long it's open during one cycle.

If you haven't taken a look at the lock linkage yet, it's probably just one of the plastic pieces attaching either end of the metal rod in place. Pulling the door cards and a couple of bucks' worth of parts should get you back in business. I'd guess one of either pn# 443839821A, 443837305A, or even 443837079F, but my money's on the first one, as they're the most brittle.

Thanks for all the help/advise with my boost issue. I replaced the MFTS and Thermostat over break and that seemed to do the trick. Next up is installing the HP2s I have hiding under the bed in my dorm room. I have read that sometimes machining of the caliper bracket or mounting ears is required. The brakes I have are from a B5 S4 ('01 i think) anyone know if that is required on these calipers?

The locks not working is kinda low on the list of things to fix, it doesn't impact drivability or safety. I think it probably is a little plastic piece of the linkage, but I can live without locks for now.