schum4

Does anyone know if there is supposed to be a screen above the engine air filter? I while replacing the filter on my new to me '06 GX470 with 125k. There was a K&N filter in stalled and some sort of thinner screen above it that seemed to be attached to the housing. Is this part of the stock intake? It looked a little dirty. Probably oil from the K&N. Should this be cleaned ?
Any help would be appreciated.

mann777

Post Images,so that would make thing more clear.

470SNC

The screen in the intake box is normal, it is a pre-filter that is factory. People have taken it out to increase throttle response. I have taken it out and added a K&N filter. The pre-filter is not really cleanable from what I can see.

schum4

Thanks guys. I figured it was part of the factory set up. I'll clean the K&N and swap it back in during my next service interval.

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nuclearn8

That's the HCF (Hydra Carbon Filter). It was installed on all vehicles due to strict EPA emission regulations/ classifications out of the tailpipe. ala ULEV etc... along the lines of why the pcv discharge air/oil mixture is now recycled back to the intake instead of being sent to a breather like in the ole days.

If you google "HCF delete mod" you'll find a bunch of threads of people who do it. The pros and cons are frequently debated on a lot of forums.

You can remove it or leave it in.
I remove it on all our vehicles with no issues at all. I figure the engine air filter is enough to provide filtered air to the engine. An engine is essentially an air pump so anything in the intake tract limits flow all other things being equal. What happens out the tailpipe at a microscopic level I'm not concerned about.

470SNC

http://www.***********.com/ja/2007/hcf.html

here's a good read on the process