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Old 07-10-2013, 03:57 PM   #11
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Join Date: Jan 2007
Location: Vero Beach

Originally Posted by poulrais View Post
Well I once had a similar problem on my 744 once and it turned out to be a disconnected wastegate actuator arm. It would build boost but the turbo was working very hard in order to do so. Do you hear a pretty loud hissing sound while on boost?
I do hear a loud hissing, but I just checked and the wastegate actuator is closing and is not stuck open. I applied pressure from my air compressor and at about 7 psi it starts to open and moves without binding or sticking - even a quick pulse of air above 7 psi and it shoots closed. I cannot move it on my own, which I understand is correct operation.

So, here's where I'm at now. This keeps getting more and more confusing.


1) Every second or third start the car will not idle until warm. Resetting the ECU via battery disconnect or fuse pull causes it to idle perfectly.

2) If the car is driven without resetting the ECU, occasional 'thoomp' sounds come from what sounds like the intake on light throttle application in neutral or on a hard acceleration above ~6000 RPM. No issues other than no boost in between those two extremes. Occasionally after one of these I will get a CEL and code 1-1-3 (incorrect mixture), but most of the time nothing.

3) Boost gauge registers pressure according to whatever I set the MBC to, but there is either no power from the turbo or very little.

Things I've done/checked:
Pre-turbo intake hose is now brand new silicone, no change in performance or symptoms.
Turbo to intercooler hose has no cracks. Intercooler to manifold hose is a solid pipe with a straight coupler on one end and an elbow at the throttle body, also no cracks in any of those.
If there are any leaks remaining in the system they are so slight that I cannot detect them.
Idle valve is working correctly.
TPS is adjusted correctly.
Throttle body is clean.
Wastegate is operating correctly.
Plugs are in good condition with a healthy tan color.

I'm leaning towards an electrical issue of some kind, maybe a sensor or ECU fault but I don't even know where else to look. That or I'm an idiot and somehow missed a huge leak, but I think I'm out of potential leaks to investigate. I just pressure tested it again and still can't hear or feel any leaks. Even a slight application of air from the compressor causes any flexible hoses to immediately inflate and there is no hissing except for the air whooshing past the turbo fins.

I am confused.

Last edited by AdmiralSenn; 07-14-2013 at 06:42 PM..
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