I was told this today by an instructor at my automotive college. He is a mechanic at a pontiac and gmc dealer and is one of the better mechanics and instructors from what I can tell. He saw the huge k&n airfilter and intake tube I put on my 3rd gen and told me to get rid of it. He explained that the K&N filters have bigger holes in them than the paper filters have (this is how they flow more air). The bigger holes in the k&n filter require that a special dirt traping oil be put on the outside of the filter to catch these particles that the paper filters with the smaller holes keep out. The problem is that the oils will blow through the filter and collect on the heater mass airflow sensor wire. This oil on the MAF wire causes anything else to stick to it and for the readings to be off. The k&n oil can also damage the O2 sensor, it supposedly does not all burn up in the engine and messes up the readings of the sensor. He says this is not his personal opinion alone, he said he and many other mechanics and technicians have had to replace the maf and or O2 sensor because they were affected by the oil. Even if you put a light ammount of oil on the filter it will get through. The filters are no good if you skip the oil because the filter will not trap all the dirt. I plan on keeping my intake setup and replace it with a big airfilter that does not use oils.

 

I dont think itll damage the O2 or MAF. If the filter is over-oiled, the MAF could accumulate oil and collect some dirt on the wires. Although I think the MAF goes through a self-clean routine after the motor is shut down. A k&n does allow more fine dirt particles to enter the motor, though, which can accelerate the wear rates of the rings.

 

Alledgedly it's the fibers movement, that helps to catch the particles as the air moves thur. In effect scrubbing the air. That's from an OLD K+N advertisement.

Beings, the last I checked they cared a C.A.R.B. exception number, one would think they'd have caught something like O2 contamination. At the GNTtype list there are hundreds of TR running K+N and have for years. On the late model MAFs, a sharpe knife will knock off most contaminants, and return the MAF to almost new. Since the EPA outlawed the cleaner for the old film type MAFs, they're not salvageble.

Paper is better then K+N if you can get enough surface area, and a combination of oil emersion, and paper is better yet. A GOOD air filter setup costs about $1,200, and you can see them on alot of Kenworths and Frieghtliners. Trouble with the good airfilters is where to put them.

 

Ive had k&ns on vehicles and I did notice they allowed some of the finer silt to get into the motor that would have otherwise been caught by an OEM filter. I remembered seeing the fine silt in the bends of the intake ducting. Not much to worry about but it does allow a small ammount of contaminates in but its a fair trade off for better flow over paper type filters.

 

In only some cases were the cars affected by the k&n. He picked on me since my setup made me a good candidate for a fouled up maf and o2. I agree that k&n works good and most will work trouble free. My instructor said that only a small % of cars had trouble with the o2 sensors (the weaker and older parts were more at risk) and the maf type cars were affected more by the ammount of oil, the size of the filter and proximity of the maf wire to the filter. The oil supposedly stick good because of the heating and cooling of the wire and some of the little particles stick to the oily wire. My setup would have the potential to foul up the maf wire. I gutted my MAF and removed the stock airfilter housing. I attached a "off road use only" 9in by 4 1/2in k&n tube filter to the end of the maf. It worked great at first and I saw a big improvment, It has since then started to run a little worse. I was told that the oil could be my problem. I plan on cleaning it and seeing if drivability improves.

 

Never seen an O2 affected by a K&N, but MAF's that aren't hotwire type can be, IF the filter is over-oiled. Typically, we clean them with electrical contact cleaner, after a good spraying with carb cleaner....

 

K&N's website says that you can over oil your filter and that over oiling would be bad, otherwise they say its safe. My teacher seems to be a little on the conservative side, he dosent like many aftermarket parts (stock natzi). I have decided to keep my K&N filter. I did not find any traces of oil in my maf. I did find the cause of the poor performance, I blew out the intake manifold gasket and a valve cover gasket. I guess I abused the 18 year old motor a little too much. Sometimes I forget to go easy on the old parts!