Do K&N Filters Kill Mass Air Flow Sensors?
September 26, 2008 by Eric
I've told I don't know how many drivers who pull into my shop with the car not running too well that the K&N Filter they got is causing them problems. Ask almost any shop operator I know and they'll tell you the same thing.
The car or truck has no power. I open the hood and spy the K&N setup. Not just a direct factory style replacement, but some monstrosity crammed into what little space there may be under there. Pull out the mass air flow sensor and surely enough there on the hot wire is a build up of gunk. Clean it off with brake cleaner and it's cured in 10 minutes.
Most airflow meters, or mass airflow sensors these days use a hot wire arrangement. A predetermined amount of current is required to hold a small heating element at a predetermined temperature. As air begins to flow into the engine the hot wire is cooled. The more air coming into the engine the cooler the wire can become. The onboard computer measures how much current it takes to keep the temperature up on the wire. The more current required, the more air there must be coming into the engine. this is a rather simplistic explanation but will suffice.
If the hot wire becomes contaminated with debris of any sort, the debris will melt onto the wire and coat it, thereby insulating it and giving the computer an erroneous reading. If you can't accurately measure the air you have available for combustion you can not determine how much fuel you need to inject. Typically it reads lean and we don't have enough fuel for much power.
If the air filter box cover isn't sealed very well, dirt, leaves and even bugs can get onto the sensor and foul it. A prime suspect is always the filter compound that is sprayed on the filters.
K&N has produced a great series of video and posted to Youtube debunking the notion of their filter cleaner causing problems. They're worth taking a look at. Video number 1 is the featured video on this site this month.
I'm not sure of the techniques the K&N guys use in their trials. I've seen filters literally dripping with the cleaner. I've seen very goofy looking installations of the filter boxes that allowed much air leakage past the filter, defeating the purpose for even having a filter. I'll be kinder to K&N in the future. They're great filters, if installed properly and treated according to factory instructions.