"Overboost" fault code, tune?

[InkandIron]

Hey there, I'm new to Audis. Posted a few other questions on the forum and I think I'm getting close to solving my issue.

To make a long story short, I bought a 2005 a4 b6 1.8t Quattro from a dealership, through a childhood friend that took it in on trade. Since he took it in on trade I have no idea what mods it had, but have slowly uncovered some of the stuff. Anyhow, I was having an issue, where I would lose boost seemingly randomly.

- Checked and relubed the diverter valve (forge)
-ran a boost leak test, no leaks

Since I had just bought it, the dealership has been great about investigating the issue. And they checked for faults. I'm getting an "overboost" fault code. I don't have the specific code. But through the scanning I found that it also is tuned. Since its "chipped" they won't go any further with this particular issue.

So basically, under normal driving conditions it pulls so good. Everything runs great. Push it alittle too hard and get the fault code, and the boost dials back, what I suspect is a soft limp mode.

Mods that I know for sure are done.

-Catback sportec exhaust
-apr cold air
-forge diverter valve (blue spring)
-tune (no idea from where)

So after all that. My questions are,

A) is it a bad tune?
B) A failing part?
C) Would an mbc help control boost pressures to a reasonable amount so this doesn't happen?
D) does an Mbc replace an n75 valve or do they work together?

Any help on this would be great. I've searched through endless threads without definitive answers so I'm asking you guys! Thanks!


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[InkandIron]

Anybody out there with some info on this? I have researched a little bit, and it seems it's going to be tough to know which tune it has, and pretty expensive to start buying other tunes and hoping for the best, not knowing exactly which upgrades I allready have.

Sounds like a new n75 valve might help to smooth out any spiking that the system isn't expecting. And the addition of an Mbc would help me dial it back if need be. I know it's probably better to change it from the ecu by tuning but at this point that seems like the most difficult option.

I don't have vcds YET but plan on getting it ASAP. Is controlling boost pressures something you can do with the vagcom software?


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[surfer1037]

Try to stay away from a Mac controller. I was having similar issues, was the n75 valve AND one of the hoses for it. Check those little hoses first, mine was split.

[InkandIron]

Yeah, that's the first thing I was going to check. Why does it seem most people have negative response with an Mbc? I'm not new to mechanics, but to these cars specifically so I'm really still learning. Is there a danger in Using them? Logically, if you use a boost controller to limit boost I don't see how it could hurt, but then again, what do I know? Ha ha. I'd like to hear some thoughts on it.


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[surfer1037]

I've never run one, to give my input. But a lot of people say to stay away from them on our car. I know our cars pretty well by now, but a lot of people know them a lot better, so I like to take the word on things.

[InkandIron]

Fair enough. I have a new n75 valve on its way, we will see if that helps the problem! Thanks for your input


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