The K&N filter uses oil on the foam to help filter. Too much oil can damage the MAF. It is well documented that it can happen. When the oil is properly applied, ie not too much, that specific problem can be avoided. Note that the filtering efficiency depends on the oil being properly applied. Also, the filter holds less dirt, ie it gets clogged more easily, so servicing needs to be done more often than with an OE filter.

The second potential problem is codes being thrown. It can happen. It is usually related to vacuum leaks.

The bigger questions in my mind are:

1) Why would you want less filtering capability? Lots of tests show that the K&N filter isn't as efficient at removing dirt. If you don't care about the filtering, just take the filter out. That is the lowest possible restriction, although it will be bad for your engine to ingest dirt.

2) Why worry about the minimal amount of restriction caused by a functioning air filter? It is completely irrelevant in terms of power production.

Some additional reading if you like. Follow the links here:

http://www.xoutpost.com/794434-post4.html

Edit: I checked the links in that post, and one is broken. Here is another link to the Duramax filter test with graphs of K&N filter efficiency compared to an OE:

Aftermarket Air Intakes/Filters - Do They Work? - Diesel Place : Chevrolet and GMC Diesel Truck Forums

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