Edit: I see that there’s already long discussions on this topic so apologies for the redundant post, feel free to comment any opinions though. All input is appreciated.

I installed a K&N Typhoon CAI about a week ago on my 2010 base model and it was fine for a few days then it started throwing a p0171 Injector bank 1 too lean code.

I checked for vacuum leaks, buttoned everything down and again it still threw the lean code.

Then I cleaned the MAF sensor and it threw the same p0171 code again waaaayy faster than before.

I’m about to put the stock air box back on to make sure I didn’t fry the MAF, but if everything works I’m at a loss for what’s causing the code.

If anyone has any input it would be greatly appreciated!

 

My 09 Fit with less than 90,000 miles has a PO171 code that won't go away. So far, new catalytic converter, MAS, upstream O2 sensor, new intake gasket, new EGR valve, throttle body cleaned, check engine light comes right back on with PO171 code. Car runs fine, gets 32+ mpg. Looking for help.

 

@Claytonjp
As you've said, this has come up before. Here's K&N's thoughts on their filters damaging MAFs.
​​​​​​Part of their argument is that testing the functionality of their filters requires equipment that only an air filter manufacturer would have 😂 But regardless, an air filter should not be able to cause misfire of one specific cylinder.
Yours may be highlighting a fault in the cylinder, accentuated by increase in airflow. If you want to continue using the filter, but don't want the CEL, you'll need to figure out what isn't functioning optimally. Should you opt to figure it out, I hope you'll keep posting!

The obvious tests would include examining spark plugs and comparing to the one from the misfire cylinder, compression test, swapping coils to see if the misfire moves, swapping injectors to see if the misfire moves, checking valve lash, checking threading on the misfiring cylinder's spark plug hole for cracks n such. You could also try running fuel cleaner in a gamble that flow through the injector on the misfiring cylinder is partially obstructed.

In a way, their air filter is proving to be a useful diagnostic tool! If anyone's deciding to get rid of their K&N, send it my way and I'll test it on my GE. Personally I'm a little uncomfortable with oiled air filters. I tried getting a K&N foamy to work on my XR650L and had trouble figuring out re-oiling procedures. It's a carbureted bike with very little in way of sensors, so there were no codes to pull, just "works or don't".
Folks seem to have tricks to it, different advisements on cleaner fluid and oiling, if they oil at all.

Fun fact! Dyson vacuums, I just found out from experience, use gauze-type filters for their post-motor exhaust (at least our newly acquired DC40 Origin does.) Outside of shape, I'd say they're the same as stock air filters on cars. Dyson actually advises washing them when they get dirty!! Well I tried it. Got out a lot of crud, though I really had to beat the filter hard against my hand to do so. Although a notable quantity of dirt got removed, and the filter did not come apart or get damaged,I gotta say, it was still nasty and I prefer replacement. Still, it's funny to think the filters I've been throwing away for years without a second thought could have been washed.

 

I

I've been running a Top Fuel intake for years now. No check engine lights ever. But it is a dry filter.

 

HPS intake for almost 3 years now....no cel's at all.

 

Forgot to address this. Not much detail about if your car, particularly your intake is modded! The google definition of Code 0170 is as follows: "The P0171 OBD-II code means that, on the first bank of the engine, the fuel system is running weak or a vacuum leak exists near this side of the engine. A lean condition occurs when the engine either receives too little fuel or too much air."

I love the idea of having all those parts on the car be new, but I don't think they all necessarily address the issue. Need more vehicle info! Mileage, problems/accidents, if the car has sat extensively or is used minimally. Knowing why you replaced all those parts would be good, too, and if the P0170 code existed before all that labor, or if it presented afterwards.

@steve37 @NWCH Nice pics! That Top Fuel intake looks particularly slick. I'm no air wizard (that was my father's bag, but I didn't learn enough) but I wonder if they were trying to increase air velocity with the duct shape. Seeing the outside diameter of the carbon fiber section inclines me to worry But it looks like you know what you're doing, and I'm pretty sure I've seen you around here for a while.
I'm glad to hear the HKS works too! Since (I think) they're similar in design, I'd like to see a side by side comparison of the HKS and K&N.
OP's got some options if buying a new intake is on the table!

 

Ya the Top Fuel piece is quite the setup. Unique for sure.

A big improvement over stock using the old butt dyno. Sounds good also.

 

I looked it up!! Can't afford, but would actually try that one. When talking intakes I largely withhold interest til I hear talk of how the air moves through the ducting. I couldn't find anywhere to buy that intake through. Import sites with huge shipping rates and pictures slightly different from yours with regard to piping.

How'd you get it?