Been having some issues diagnosing SAI codes (P0411) on my friend's 2.8 C5. It's an ATQ. I've gone through the whole system and I still get an incorrect flow code and "System Not OK" in VCDS for both banks when I run the test in Basic Settings.
I started with replacing the air pump, was full of water that was brown due to rust. Also replaced the hoses going to and from the air pump. Pump will turn on when testing the relay in Output Tests in VCDS. Can feel strong rushing of air with pipe disconnected from air pump. So it's safe to assume that the relay and fuse are fine if it's running during the VCDS test?
Then, I checked the combi valves, both were so caked with carbon that a can of carb/choke cleaner didn't help. Pulled a set from PnP and bench tested them with MityVac hand pump. Held vacuum and valves opened when vacuum was applied. While installing them, I used some gasket paper (made holes and trimmed edges to fit) and a very light coat of RTV to hold it in place when installing on the cylinder heads.
Double checked vacuum line routing, according to the diagram under the hood, everything looked okay to me. Only thing that I noticed was the blue check valve seemed to be backwards. But the check valve did work, could only suck air through on one side. Put that side towards the vacuum source. Also checked to make sure that there was vacuum from line while car was running. Vacuum lines had been previously replaced with silicone line.
With the output tests on VCDS also checked the N112 solenoid valve, could hear solenoid clicking and verified that vacuum could pass through when it was energized.
So, even after all of this when I run the test in Basic Settings (channel 77 for one bank, 78 for the other), it will run and then the result is "System not OK" for both banks. Then fault codes are stored for SAI insufficient flow on both banks. I noticed that while the test is running, MAF % reading while go down to -100%~ or so, VCDS states specification is -100% to 50%. I would imagine that -100% would show that extra air is being sucked from the air box into the combi valves (but not necessarily into the exhaust stream)?
The only thing that I can think of is that the hand made gaskets were installed backwards and is impeding airflow or the passages in the cylinder heads themselves are clogged with carbon. I don't believe the passages are clogged however, since cylinder heads mating surfaces were decked for a head gasket replacement a few months ago. I believe they were hot tanked, so that would remove any carbon buildup in the passages.
I apologize in advance for the wall of text. I'm at my wit's end with this and can't figure it out.
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Originally Posted by DeltaAlpha9
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