Need help troubleshooting low boost

[p_latend]

Hey all- Over the past few months I've been getting low boost error codes. I'm running the APR 93 octane program (2004 AWM w/Tip). Right now I'm lucky if I can hold 10psi under full load.

I've checked for boost leaks and all seems well there. I installed the TT DV (the original one was fine but I figured it was time to upgrade any way).

I am at the point where I want to check the N75 and the waste gate. I've read quite a few posts regarding how to disconnect a hose from the N75 valve to disable the boost control. Some posts say to disconnect the line from the N75 to the waste gate actuator and then plug the open N75 port.

Other posts have said to disconnect the line running from the N75 to the turbo housing.

Which method is correct? Or are both methods essentially doing the same thing?

As a follow on question to the above, are any lines left open(unplugged) when doing this?

I understand I need to be careful to not severely over boost when I perform this test.


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[zak99B5]

You can just pinch the N75 to actuator hose and the wastegate should stay shut. Careful with the throttle. I'd the flapper valve is toast, you still will not make much boost.

When I had a low boost issue, it was the wastegate sticking open. Apparently it can get hung up on the heat shield. To see if the actuator is working you can take off the air snorkel and rev it in neutral to like 5k then let off the throttle. You should see the rod move back when it opens the flapper and return as the revs drop.

[p_latend]

Thanks! I'll give that a try tomorrow and see if I can figure out what's going on.


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[John_E]

Have you access to VCDS/VAG-COM? Could it be in limp/protective mode, e.g. because of a bad MAF or O2 sensor?

[p_latend]

No, I just have a generic code reader.

I'm waiting for Ross Tech to release the hardware for mobile devices before I purchase it.


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[p_latend]

No, I just have a generic code reader.

I'm waiting for Ross Tech to release the hardware for mobile devices before I purchase it.


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[Steve in Chicago]

Which method is correct? Or are both methods essentially doing the same thing?

Both methods do the same thing (interrupt the pressure signal from the compressor to the waste gate actuator).
One is before the N75 and the other is after the N75.

Whichever you disconnect, make sure to plug off the side with the pressure signal, otherwise it becomes a small boost leak.

[p_latend]

Problem solved.

One of the bolts that fastens the actuator to the turbo housing fell out and allowed it to move about 1/8"-3/16" away from the turbo. That must have prevented the waste gate from closing all the way.

Sure is nice having the boost back. Thanks for the help guys.

Phil


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[zak99B5]

Everyone loves a happy ending.

[p_latend]

Especially when they are free!


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