Awag

For some reason, while I was messing with my trunk release switch (fixed) and my windshield wiper fluid system (still not working right -but that's another story), I decided to check my air filter and realized it needed to be replaced. I had heard a lot about K&N cone filters and such, but after doing a little research I decided to go with just the oem replacement air filter that K&N offers. Of course I disregarded all of the comments on threads claiming the little to no improvement that the filter provided for the money, because I'm a teenage boy, and bought one anyways.

I expected very little to no improvement, but what I had not expected was my AFM sensor going bad.

After taking it to Rennsport KC to get it fixed (they did a great job fixing it and deleting my catalytic converter too, by the way), I was advised not to mess with using the K&N filter.

I researched for days before buying the filter and never ran across one person that said it ruined their AFM and kept their car from starting. The closest thing I found after was someone complaining that, after over-oiling their filter, the sensor was "bogged down" with oil and the throttle response wasn't the same.

So, I guess what my question is: was the AFM going bad a direct result of using the K&N air filter, or was it just mere coincidence that it went bad?

Thanks for reading and sorry about the long post. Thanks!

-Awag

86 951 Driver

I have been running KN filters in my cars for years without any issues. My dad had a 1983 944 back in the 80's to early 90's. He ran a KN air filter without any issues. RennsportKC know their way around a 944 and Porsches in general. The great air filter debate has been going on forever.

william_b_noble

I don't think the KN filter per se will hurt the air flow sensor, the sensor is just a vane, but there is no possible reason to change unless the OEM filter becomes unavailable - the K&N cone filter has less area (if memory serves) than the original filter, and it draws air from the hot engine bay instead of through the snorkel that brings in cool outside air. And, the orange cone thing looks really stupid - I use one in my Suburban, but I got it for less than the cost of a paper filter and it fits inside the same housing. If K&N makes a filter that fits in the Porsche housing, not the stupid cone, then you may find it useful if you are in a dusty area.

Butters944

Read the OP more carefully.. He is using an OEM replacement k&n that goes in the stock housing. Your argument is irrelevant...

To the OP, I can't see how the problem is more than a coincidence. What could the kn do to mess up the afm..? I can't think of anything.

Awag

That's exactly what I found after researching online -the cone is useless unless you can make a separate housing to block off the hot air from the engine. But, the housing alone can cost up to $100, not to mention the cost of a decent cone filter that fits our cars, so I decided against it.

Awag

That's why I specifically posted this thread, I found it odd that the filter would do that to the AFM. I was hoping someone else might have dealt with this before. Like I said before, the only thing I saw that might make sense is that over-oiling the filter could get some oil in the AFM and mess with it, but mine was pre-oiled and my AFM completely went out. Then again, it is a 26 year-old car, it's possible the AFM just went bad, but I thought it was too much of a coincidence.

Gawernator

Coincidence. The filter comes pre-oiled correctly, I dropped one in a year or so ago ($30-40 off eBay) and have had a perfectly running engine. I don't know if it makes any difference at all, but I don't have to buy a new filter and it looks cool. I like the color red. lol

FjarrKontroll

My car came with the K&N filter so I've done quite a bit of research on it to cut through all of the contradictory forum replies.

1. Basically, as long as it's re-oiled properly there is no issue.
2. If it hasn't been re-oiled since the factory, it won't cause a problem because they do it perfectly.
3. People like to make it sound like it sprays gallons of oil all over everything and gums it all up. That's ridiculous. If any got away due to over-application, it would be a tiny amount, in fine mist-like droplets over time. Unless you re-oil it and put it back dripping with oil.
4: The "It will ruin all your air sensors" thing is bunk. Some types of MAF sensors wouldn't take kindly to oil, but again those types of problems don't occur if you oil it properly.
5: You can pour used motor oil into the intake of a 944 (except the S2, but I don't really recommend it anyway) and it won't harm the AFM. There's nothing to harm, it's just a spring-loaded flap and a temperature sensor. If it gets gummed up somehow, there are other things to worry about but you should be able to clean it fairly easily.
6: I don't know where the thread is now, but I saw one with dyno results confirming zero performance increase with the K&N filter. Shouldn't surprise anyone except the people who drop the stock filter box in favour of a hot air intake.

So I say coincidence combined with 26 years of being on the road.

Gawernator

Some people tell me the engine is slightly louder with the K&N, guess I haven't noticed

odurandina

my first question would be:

could the AFM be negatively affected by a freshly oiled K&N filter ??

especially with a liberal helping of oil ?

william_b_noble

no, the oil from a filter will not affect the air flow meter - it is a spring loaded vane, not a thermistor as found in a Mass Flow Sensor as used on later cars. But spending anything on the K&N is silly.

One way the K&N could cause trouble is if the lack of support of the air flow sensor causes it to sag, causing a leak in a old J-tube, or if it moves the sensor revealing a wiring problem.

For these cars, stick with stock for the filter, honest

Gawernator

Pretty sure Odur's last post was a troll dude haha. The K&N air filter does not cause problems. The blown out seals in your old Throttle body are leaking in more oil than the filter ever will, haha.

PorscheDoc

The K&N filter will not harm the AFM.....but the reason they make a little better power and mileage is because they filter less. Smear a glob of grease in the intake between the filter and the throttle body. Run it for a week and remove and inspect what is caught in the grease. It will show you how little a K&N filter actually filters. If you want that stuff running through your engine then that is up to you The stock filter works just fine and does a much better job of filtering.

944Ross

I like to trot this out in these discussions. Written by the owner of Roadrunner Engineering, who is a mechanical engineer with excellent credentials:

"There are several air filter systems promising more horsepower by allowing more airflow. Most of these filter elements are of the cotton gauze type, which are oiled to enhance dirt capture. The good news is that the filters do flow more air for the same size as a standard pleated paper filter. The bad news is that they also flow more dirt. Using a well known manufacturer’s own data for one of these filters vs. the SAE data for a standard pleated paper filter, and calculating the difference in filtering for a 302 cubic in. engine traveling 12000 miles, the difference was over one more pound of dirt ingested by the engine with the high flow filter! This is particularly harmful on tow vehicles which may spend long times at high throttle opening in dusty conditions. There is definitely a trade-off here. You can often maximize airflow by eliminating the filter altogether if engine life is secondary."