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Long story - but interesting. My 2009 E320 has a check engine light, a code 2633 (mass air flow sensor drift under engine load.)
While diagnosing the issue, I discovered and fixed the following:
Turbo intercooler hose had a crack / leak, replace both hoses and pressure tested the turbo side of the system to 20 psi.
PCV valve diaphragm was torn, replaced the assembly.
Air filters were filthy, replaced them both.
Replaced the turbo electronic actuator, don't know if it was bad or not.
This did not fix the CEL problem. Here are a few extra things I checked:
The swirl flap motor has the correct resistance across the loads, and electronically it appears to work. The code(s) do not reflect any problems with this component.
The turbo does not appear to have any play in the shaft.
Clearing the fault code has no effect, and the CEL remains lit even after clearing but before the engine is started.
The car has been unusable up to this point due to the CEL and reverting to limp-home mode after 5 minutes or so. I hooked up my iCarSoft i980, and set it up to record some of the boost information while driving around the block. I extracted the data file from the i980, and saved as a text file. I wrote a custom Java program to parse the data and dump into a format suitable for a spreadsheet. Looking at the data, it appears I have an enormous amount of exhaust back pressure, which would cause the problem I'm seeing with the CEL 2633. Does anyone know what the exhaust back pressure should be? Here's the graph:
According to these results, the exhaust back pressure is spiking to over 40 psi! That seems excessive to me, but I have no idea what's normal. If this is unusual, then I can pull the DPF and have it cleaned. But I don't care to spend the time and money if this is normal. Does anyone have any experience with what the exhaust back pressure should be on a OM642 engine under load? Any other comments about my results? Please help.
