Boost Leak, Strange Noises, and Other Intake Madness

[Zk20495]

Hi all:

I've been experiencing some interesting boost/intake issues with my B5 for a few months, and I've finally spent enough time reading, searching, and getting frustrated to post about it.

The car: It's a 2000 A4 B5, 5SPD, Quattro, and 1.8t. So ATW engine code and all that jazz, plus some mods. The key ones I think here: K04-15 turbo (literally brand new), GIAC tune (approx. 20psi), testpipe, cat-back, TIP, and DV.

The problem: Issues started out as just randomly throwing me into limp mode (regular limp, 5-7 psi), and then letting me back out after a few days. Then days turned to weeks, weeks to months, and eventually catching a hard limp mode to ~2 psi. It's been throwing a few codes - P1556 Charge Pressure Control: Negative Deviation (indicative of a leak), P0140 02 Sensor Circuit No Activity Detected: Bank 1 Sensor 2 (testpipe, an anti-fouler didn't fit ), and P0411 Secondary Air Injection System: Incorrect Flow Detected (I deleted SAI after my pump failed).

What I've done: After limping 400+ miles home from school, I have replaced the N75, logged my MAF which appears to check out, followed Walky's wonderful vacuum delete/simplification guide (found here), and even had to (yep, just had to) go K04 after my wastegate failed.

What persists: After all of that fun work (note: sarcasm), I am currently experiencing about 7 psi of boost, though it feels less potent than normal limp mode, which is why I suspect a leak. I am also getting a strange almost mooing or groaning sound just before hitting positive pressure, and if I hold part throttle correctly, it will continually make this sound. My boost gauge shows it at right around -6 inHG. I've got a feeling it has to do with my vacuum simplification, but I've been wrong before. Lastly, every single code is still being thrown (no new ones) to my knowledge, I'll double check and edit if needed.

The plan: This weekend I plan to go back through my vacuum work with brand new lines for my sanity's sake, replace any check valves not sealing, and try my hand at a boost test (following a similar method to this). I may also look at the PCV system, as I've been smelling some oil and forgot to check my pancake valve during the turbo swap; however I do have to drive this car daily, aside from the occasional long weekend, so I can't go ripping out manifolds to really dig in.

So why post?: This is just getting really frustrating, and it also helps me think through things when I write them out. I figured I'd write up a post and see if anyone had any similar issues or possible suggestions, since our cars are so terribly confusing to diagnose. Any help would be much appreciated, and I'll be posting anything I find this weekend on here as well.

TL;DR: I think have an intake tract issue somewhere, help me find it .

- Zack.

[MetalMan]

Also might be worthwhile to test your DV.

[Zk20495]

Also might be worthwhile to test your DV.

I was thinking about that as well, although I'm not exactly sure how to go about it other than blowing on it to see if it leaks. That's all I did to my R1 when it was blowing through. I'll look into it.