Hello, does your under-boost code go away if the purge valve is unplugged or blocked off? That valve is very loud, but if the cat has started to fail and is restricting the exhaust, which will also cause a lack of air into the engine, along with the fact that the turbo needs exhaust gas to run the turbo, forcing air flow into the engine. You may want to do a back pressure test to see if the cat is restricting the exhaust. Another check is to graph the rear oxygen sensor, if it has a high frequency fluctuation, and not a steady voltage that is a sign the cat is not doing its job.
Block off that Purge valve from the intake first and see if the under boost code doesn't set again, you should be able to monitor the boost pressure on your scan tool as well, clear the codes first, and pull up the Boost pressure, rear 02 sensor (graphed) data PIDs and see what they read with the purge valve blocked off and unplugged.
Ill post some causes of a P0299 code for you, and it would be interesting to see if a clogged cat is the real fault here.
You can also do a VE test, which would tell you a lot about how the engine is breathing.
How does the vehicle drive?
here is a VE calculator test. Very effective in diagnosing a cat issue before going to a back pressure test.
https://atgtraining.com/atg-volumetric-efficiency-calculator/
Tuesday, April 15th, 2025 AT 12:56 PM