K&N air filter

There is a recent thread in the yahoo group PTS (Prius Technical Stuff) where someone who was using a K&N filter had to replace their MAF sensor because it was contaminated. Bob Wilson has the old part and is going to investigate the actual cause of failure.

I have run K&N filters on other vehicles, but I don't see any advantage to using one on a Prius performance wise.

 

Photos from failed MAF:

Air flows through the thermistor on the side to get the ambient temperature. Part of the air splits and flows through the sample tube.


The air flows past a 'hot wire' whose resistance changes as heat is drawn away. The ratio of the thermistor temperature and the heat lost determines the air mass flow.

The risk is a foreign contaminate may accumulate on the hot wire, say motor oil additives or dust or debris entrapped by oil. Either can change the rate at which the air flowing past the hot wire is lost. In theory, the exhaust O_{2} sensors could adjust the calibration.

The connector has five pins, ground and a pair for the thermistor and a pair for the wire. The hot wire and thermistor resistances measured 27k and 2.1k ohms.

Air filters have two characteristics: (1) entrapment of dust and (2) some air resistance. I have no idea about the relative effectiveness of the K&N versus a paper filter on entrapping dust. For now, I simply change my paper filter in the fall to get rid of pollen, dust and insect bodies.

As for air resistance, our Atkinson engine cycle is less sensitive because part of the fuel-air charge is pushed back into the manifold with each cycle. This partial charge is picked up by the next cylinder but again, part is pushed back as the intake valves are held open for part of the compression stroke. In contrast, an Otto cycle tries to draw in as much fuel-air as possible and reducing the filter air resistance helps Otto engines when under full throttle. In partial throttle situations, the filter is a minor player.

It might be an interesting experiment to put a K&N filter in front of a paper filter. Then after a year of service, inspect the paper filter to see what it captured. However, I have no commitment to K&N filter analysis.

Bob Wilson

 

Hi Bob

Do you think that cleaning the element will fix the problem, or is it permanently damaged?

I know that with other vehicles (Ford Explorer) the element can usually be cleaned successfully.

 

I suspect it can be cleaned but I want to setup a test fixture for testing it.

I have some filter paper coming. What I may do is spray contact cleaner over the area and filter the residual fluid to see if there is any evidence of 'stuff' coming off the sensor wire.

What may make more sense is to get some throttle plate cleaner and see what it does. It may make more sense when cleaning the throttle plate area to deliberately spray the air inlet side of the MAF sensor. At least now I have a test article to see what happens.

Bob Wilson

 

You can get a can of Mass Air Flow Sensor cleaner at your local parts store for less than $10 and the can will last a long time. I have always pulled the MAF every other oil change and squirted the actual sensor (less than 5 min.) on most cars. It may be overboard but I like doing my own maintenance so I can do the few extra things that a quick service place wont do.
I pull the air filter before starting my oil change service and get it washed. After sitting for the time it takes me to drain the engine oil and replace the oil filter, the air filter (with the help from a blow dryer on low heat) is ready to get re-oiled and go back into it's hole.
bwilson, your comments make sense and there may be very little performance benefit? I know there are other brands besides K&N and assume they are all compatible (not wanting to push a specific brand here). I guess if I find myself replacing the MAF sensor, I will ditch the reusable filter for paper.

 

Earth to the people.. U wont ruin anything dropping it in.. GET one 56 or so $ worth it and u might/will need/want to mod the air box more for more airflow. If you follow the hose that leads off of it to the left goes to a white container.. this container if taken out of car SUCKS.. it has a little hole at the bottom for air.. VERY RESTRICTIVE.. AIR boxes in cares are made to be quiet, not efficient (vested interest in oil companies cause this).. so take it out LET THE car BREATH