Boost Loss / Turbo Flutter
 

Hi guys, newbie here!

A little background of me and my car. I bought it about a month ago and have never owned a turbo so thought all was good and dandy. I did a waterpump (coolant leak) replacement as well as timing belt myself. Dealt with some low oil pressure issues which I resolved doing a diesel flush.

That is the extent of my mechanical know-how.

Now, I was looking into my car a little more, it's a 2000 A4 1.8tqm with a K04 and GIAC J31 chip, and found out it should be putting out 18 psi+.. Well it's only ever put out 7. Every time, any rpm, 7.

Now I am starting to get a turbo flutter as well.. I am not sure if this is new or not, but I just noticed it.

I have CEL, but the fault code's I am getting at 3 O2 related and one SEI one.

I just replaced the DV with a Forge one, and that didnt change the flutter.

I am thinking maybe a boost leak (I have no air compressor to test, and that wouldnt explain the flutter), or maybe something with the actuator/wastegate (read online someone had a similar issue due to bad wastegate)

I dont have a garage at my place, or a large tool selection, just my basic toolbox, and am darn close to bringing it into the shop, as it is my DD and I need to up and running.

Can anyone shed any light on these issues in a easy to check way, so I can save some cash?

Thanks!

You can make a boost leak tester. Search on forums search option. There's a thread how to make it. It basically puts air into your intake at a certain psi so u can hear where air is leaking from. But about 7-9 psi is stock boost so are you sure your chipped? Take out ecu etc or u bought it "chipped". Ive seen that happen before. Im not so sure about turbo flutter but wastefaye sounds accurate and you may need to get a new turbo. The wastegate malfunctioning would also most likely cause less psi so u could try a turbo rebuild as well unless u just want a new one.

Here's my thought on 7psi: I believe the K04 typically has its wastegate set at 7psi. If you have a CEL on (especially for O2 sensors) you are likely in limp mode. When in limp mode the N75 valve is essentially non-functional so you will be at the mercy of the wastegate... which in your case is 7psi.

Which O2 sensor codes are they? If one of them says you're running rich then a boost leak could be a culprit. If lean, then maybe your primary O2 sensor needs replacement. If it is that the O2 sensor activity is intermittent, replace the O2 sensor that is causing that code.

You can buy just a wastegate, I don't see why a whole turbo rebuild would be necessary?

And I think my N75 is removed, as my vacuum is going straight from intake manifold to my DV (bought it this way). So how would I adjust the wastegate higher? The part that throws me off is the PO claims he was making 18+ psi. :/

Im not 100% sure how Audi does it, but you can go into limp mode without any of the vacum lines on the N75 going anywhere, for the longest time I had my turbo hooked up only to a forge unos, and time to time I would hit limp mode.

With the car warmed up and idling in neutral, what does your boost gauge read? It should be -18 to -22 in Hg. If it's higher than that, you have a boost/vacuum leak.

Just to clarify, by "higher" he means closer to zero. Also, I have a boost leak tester I would be happy to loan you if you promise not to steal it :)

Think you got the N75 mixed up with the DV control valve. The N75 controls boost to the wastegate, and doesn't hook up to the DV. One end of the N75 goes into the turbo inlet pipe, one end has a line connected to the turbo compressor housing, and the third port on the N75 has a line going to the wastegate. It also has a 2-pin connector which is the signal from the ECU to open or close the N75 (it is just a fancy solenoid). So if you're in limp mode the ECU will keep the N75 open all the time so that the wastegate and compressor reference line are basically connected directly, allowing the wastegate to have full control over how much boost the turbo can achieve.

Haha of course I wouldn't steal it.

I will check the vacuum gauge when I get home from work..

I was mistaken about the N75 (was thinking something completely wrong)..

But on what kraylon said, I did check out my N75 this morning. It IS routed to itself, but the weird part is I have no MBC....

Instead, the part on the compressor housing where the N75 should be connected is connected to the wastegate where the N75 should be connected.. with the N75 connected to itself..

This would then cause it to line up with the 7 PSI default for a K04 that MetalMan suggested above? LEaving the PSI completely up to the wastegate, which would just allow the 7?

This setup makes no sense to me unless the PO had a MBC and just grabbed it off and connected the two parts together as a quick fix to sell it.

Anyone have any thoughts on this new information?

I know, just had to say it :)

Sounds like that's exactly what he did. Kind of a dick move IMO. You can put it back together like it's supposed to be and see if that helps. The longer port on the N75 should go into the turbo inlet pipe. The two shorter ones go between the boost source on the compressor housing and the waste gate.