mikeys

First post as I just bought my first Audi, did some research and could not find my question answered so I'm hoping someone might know of the top of their head.

Background: Stock '98 A4 AEB 1.8T 67K miles bought recently and has never had boost. Bought boost gauge and shows at most 1 lb boost under all circumstances.

Went through the usual checklist to see what it might be:
- Upgraded diverter valve (DV) to Bosch 710N (when timing belt changed right after purchase)
- Replaced vacuum hose from intake manifold to DV (this was collapsed but no effect on fixing problem)
- Did boost check with PVC fitting and it held pressure to 15 lbs with no leaks
- Checked resistance on N75-C valve and 29ohms and could not blow through the long pipe (I'm upgrading it to N75-J while I am at it)

So I decided to pull the turbo (a bit a a pain) and it appears to be fine (impellers spin freely).

When I checked out the waste gate, I applied pressure to the diaphragm with a bike pump and it will force the waste gate open.

However, without pressure on it, I can move the waste gate actuator rod back and forth and there is not any tension on it, (meaning I can just rotate the whole turbo housing vertically and the waste gate will close under weight of the rod, and if I flip it 180 degrees it will close the valve).

So my big question (and I think that this might be the problem): is there supposed to be some spring pressure on the waste gate(or should the rod be connected inside the diaphragm so it doesn't move freely) to keep the waste gate valve closed until boost pushes the diaphragm rod and this forces the waste gate open?

If so, this would explain the problem... If not, I would very much like to hear suggestions on what it could be. Also, now that I have pulled the turbo, is there anything I should do to check its health.

Best,

Mike

mikeys

Meant to say: However, without pressure on it, I can move the waste gate actuator rod back and forth and there is not any tension on it, (meaning I can just rotate the whole turbo housing vertically and the waste gate will close under weight of the rod, and if I flip it 180 degrees it will open the valve).

mikeys

So I have found out that indeed the waste gate actuator/diaphragm is bad and should require substantial effort to open the waste gate (without air pressure). So, if you lack boost, this might be one additional thing to check.

I am now looking for a working waste gate actuator from a K03 turbo that someone has lying around from a turbo upgrade and willing to part with it at a reasonable price.