Looking for some troubleshooting advice and maybe some input from people that have had experience with a blown turbo. I had everything working fine until I removed the LIM to replace the coolant O-rings which required removing the turbo from manifold. I don't have much garage time to work on it, so I'd like to have some input on what to look at when I do get a chance. The turbo is a hybrid T04b-exact trim unknown and RTek 1.7 and has not given me issues like this before. Twin scroll and emissions intact (Thanks Cali!).

Symptoms: Runs lean and little/no boost.
-The car won't build boost and generally has higher vacuum than it used to while accelerating.
-At full throttle, vacuum goes to zero and kinda hangs there until about 6k rpm then it will finally go positive about 7 psi. (It used to go positive with any significant amount of throttle input)
-Narrowband says it is right around 14.7 AFR almost all the time. While narrowbands are normally useless, if it says it is within the narrow range that it actually works, I listen to it.
-Idles and runs just fine with 19in of vacuum
-Turbo does have some oil blowby, but it worked fine before removal. Seems to have minor, but acceptable shaft play.


Tests I've done:
-Fuel pressure is 45 psi while running (walbro 255)
-TPS is set correctly
-Throttle cable fully opens throttle
-Secondary throttle butterflies seem to operate smoothly
-Electronic boost controller does not change the behavior
-Tried to pressurize intake and sprayed connections with soapy water. Couldn't find any leaks. May take it to a shop and have it done professionally to be sure.
-Quadrouple checked vacuum lines and gone through cans of carb cleaner looking for leaks.

Does this sound like a stuck wastegate?
Is there anything else that is supposed to close when switching from vacuum to boost?
Is this the behavior of a blown turbo? (I doubt it because it sat on the workbench and then went back on)
If it was a boost leak, the AFM would read higher than actual and run rich, correct?

Thanks for reading my novel and any suggestions in advance!

 

Be sure that the wastegate actuator rod that runs from the wastegate diaphragm to the wastegate flapper arm is secured.

 

It is definitely secured. However, it is a nice rusty c-clip, so I still need to check if something is binding and holding it open. I appreciate the input.

 

Had some time this weekend and didn't find any binding in the wastegate or actuator.
I'm suspecting I have a recirculating boost leak through the BAC. This is the only way I can figure I am losing boost but keeping the closed loop AFR's. I've tested it and know it actuates when given power, but I don't know if it seals completely. My understanding is it should be closed with key off but with the key on, pulsing so the voltage at pin 2Q (on an s4) reads approximately 9v.

Is there any way to check if the turbo is building boost but it is being vented somewhere else? Can I tee a boost gauge to the wastegate actuator line off the compressor housing or would it read the same as the UIM nipple?

 

check your compression first.

any idle issues?

 

Compression is good. All even pulses and 95~100 psi on both rotors. They are the same readings as before I pulled the LIM.
No idle issues at all. Starts easily and holds a steady 19 in. of vacuum on stock and aftermarket gauges.

 

hmmm so sounds like its def. not the motor. i would swap on another turbo if you have one lying around.