SloopJohnB@mac.com

Is there a manifold pressure sensor you can check with vag-com or a separate multimeter?

Braap

It looks like there is, group 75 and 76 on the measuring blocks can get the intake manifold pressure. What should I look for when I do this? Engine under load, idle, rpm? I'm at work now, so I won't be able to check until tonight, but I'll check and post the results. Also tomorrow I'm going to test for boost leaks and see if there are any (I hope there are). Thanks for the help!

SloopJohnB@mac.com

This is one of those shady tree garage comments that may or may not be relevant, but here goes.

If you KNOW your engine manifold pressure is not 13psig, i.e., 13psi over ambient air pressure, i.e., you have a vacuum under idle, yet vag-com indicates you have 13psi boost (dunno if vag-com actually tells engine manifold pressure...FWIW, absolute manifold pressure of 13psi is almost atmospheric so you could have 1.7psi vacuum or about 3.5in Hg vacuum, still too low a vacuum reading...but vag-com has no manifold pressure sensor 'bad' codes, I would replace the manifold pressure sensor anyway.

This might help:
http://www.permoveo.ltd.uk/tabid/122...i/Default.aspx

Braap

Interesting...

I found something else today, I logged some more data and saw that my wastegate duty cycle was 0% the whole time I was driving. I did some 3rd gear pulls, highway driving and city driving, all 0% duty cycle on the wastegate. This makes me think either I need to replace the wastegate or there is a leak in one of the wastegate lines. Does this make sense?

If the wastegate isn't opening, it would cause me to overboost, correct? Also, I read that the boost pressure that Vag-Com spits out doesn't account for the ambient air pressure. So since my ambient air pressure is 1.0 bar, then the boost pressure would be 1.0 bar less than what it is reading. So I am idling just under 1.0 bar, meaning I have little to no vacuum, which to me links back to what I said earlier. This also means I am peaking at about 11-12 psi boost, which is much more believable than 27psi.

Any thoughts?

Braap

Sorry for posting again, but another important piece of info:
When looking at the specified boost vs. actual boost, the actual boost is 600-1000 mbar more than specified when under load. Another sign of a leak possibly?

SloopJohnB@mac.com

sounds like you have a broken hose to the waste gate.

Wastegates are controlled by a diaphragm motor and rod...the pressure that goes to the wastegate is usually not the manifold pressure, i.e., the waste gate is set to a base pressure, perhaps 7-10 psi, essentially the safest minimum pressure the engine can operate at. Thus, if the waste gate sees full engine manifold pressure, it limits the boost to 7-10 psi.

So, how does one get MORE than the base setting? Well, at least two systems, volvo and saab, bleed off the waste gate signal from the manifold so the waste gate doesn't SEE that base pressure and therefore the waste gate doesn't open. The ECU therefore controls boost pressure above the base setting. I wouldn't be surprised if Audi does the same.

In your case, it looks like the waste gate isn't getting any signal at all and is therefore closed so you're getting whatever boost the turbo makes and the throttle allows. Not good if you have a lead foot.

I put a #1 connecting rod through the block on a good 2.4L L4 Volvo engine that had a broken waste gate pressure line...the boost gauge spun round like a tach and pegged at maybe 30psi....the engine must have been pulling over 350hp for maybe the three or four seconds it lasted...BANG! My heavy foot caused it as well as failure of the system to control the boost.

SloopJohnB@mac.com

Yes. You have a leak somewhere or a bad controller to the waste gate...the controller bleeds off the waste gate signal to get more than base boost.