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So here's the thing. I've had k&n on my 07.5 duramax, 95 silverado 1500, and several other toys. I've never had any issues. I now have a wcfab compound kit with their intake dry filter. Anyway I had heard of all these horror stories about filter oil plugging up the MAF sensor. Never happened to me. After a while I kind of was wondering how much someone would have to put to plug the MAF sensor up so I put twice the oil it needed on there and still never gave me a sensor error. The important thing with the oiled filters is that they are properly oiled all over. Lack of oil will get you dirt in engine.
For what it's worth, the WC fab filter has an outerwear prefilter that would perfectly go over a k&N or spectre filter if anyone is looking for a good prefilter. I believe they sell it by itself.
 
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2007 classic LBZ GMC Sierra sle2 crewcab longbed 4x4 Allison
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I have a 2021 gmc siera with a duramax. I just put in a k and air filter and now I have a fault that says check system. I took the old one out saved it just in case and just plopped the new one in and fired her up. I think it said new filter on the dash and I clicked yes but now every time I start it. It says check system. I thought this was a no brainer. Anyone experience this?
Yes I have you need to pull out the maf sensor clean it inside with tips and mass air sensor special cleaner. Make sure there is minimal oil on just outside of K&N filter then reset code with scanner off take both grounds off batteries for 5 min then reconnect to rest OBD II computer module.
 

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2007 classic LBZ GMC Sierra sle2 crewcab longbed 4x4 Allison
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Yes I have you need to pull out the maf sensor clean it inside with tips and mass air sensor special cleaner. Make sure there is minimal oil on just outside of K&N filter then reset code with scanner or take both grounds off batteries for 5 min then reconnect to reset OBD II computer module.
 

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See the air efficiency vs. filtration effectiveness link shared by K&N on questions I had regarding the same questions and issues shared on this thread. There are also some significant head-to-head testing done on uTube with K&N [oil cotton or synthetic gauze filtration vs. paper by manufacturer] AC Delco ranks at or near the top on filtration effectiveness but lower on air volume thru-put efficiency. You all can look for yourself, HOWEVER THE SHORT STORY IS, for air filtration any PAPER is better than oiled gauze. AND oiled gauze is only effective for particulate sizes greater than 7 micron in size [per the studies mentioned on the uTube testing, also note K&N's testing particulate size]. This means that unless you're using your diesel in mostly clean environments.... you are going to pass into the engine significantly more fine grit/dust... like gypsum dust and clay/mica particulate with an oil gauze filter [per uTube testing]. For reference, a HEPA quality air filter must screen out 99.97% of all particulate larger than .3 micron; so we talking about "miles" of size smaller.... approximating an order of magnitude difference in size smaller. From a less restricted air intake basis, K&N ranked highest/best.... so more air, less restriction, but also less effective air filtration. So.... like life, trade-offs are ever present!

FYI, I now have several hundred dollars of other K&N application filters sitting on my shelf as I've gone back to paper. Also, I never had problems with the "oil" messing up the MAF sensors in gas applications, however I understand, thru reading numerous other posts on this matter, that upon cleaning and reusing the oil gauze K&N filter, one can "over-oil" the filter and that will cause problems. The L5P computers may be more sensitive to contamination than gas MAF sensors.....I don't know.

Caveat: My comments are not on an L5P Duramax K&N filter application.
 

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I have a 2021 gmc siera with a duramax. I just put in a k and air filter and now I have a fault that says check system. I took the old one out saved it just in case and just plopped the new one in and fired her up. I think it said new filter on the dash and I clicked yes but now every time I start it. It says check system. I thought this was a no brainer. Anyone experience this?
Put an S&B in if you can. K&n always seems to cause issues.
 

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I tried a K&N, came oiled from the factory. On the first tow up a grade, threw a MAF code and ran terribly. Cleaned the intake and back to stock, no problems since.

FWIW, I only use AC Delco air filters, I put silicone grease on the seal, and change them as soon as they start to get dirty. I check for dust (a little WD40 white paper towel) in the intake with every filter change and I've never seen any in a 189,000 miles.
 

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Doesn't matter what you put in. If it's high flowing the new trucks will throw a code unless you follow the disable instructions beforehand. No doubt done just to annoy new owners regarding changing anything on the truck.
 

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I have a buddy that owns a diesel shop and he says he has replaced more turbos because of oil filters because people oil them too much and it gets on the turbine and throws it off balance and eats up the bearings. That to me was enough to say ok dry filters is key lol. I had a s&b on my 13 and it was awesome I only changed it once in the 5 years I owned that truck but I had the sock for it which gets out all the big stuff. That being said I think k&n is awesome for the right application but not for the l5p unless they offer an oil less filter like s&b ( I have not done research so they might) im just saying oil in the intake is your enemy
 

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I have a buddy that owns a diesel shop and he says he has replaced more turbos because of oil filters because people oil them too much and it gets on the turbine and throws it off balance and eats up the bearings. That to me was enough to say ok dry filters is key lol. I had a s&b on my 13 and it was awesome I only changed it once in the 5 years I owned that truck but I had the sock for it which gets out all the big stuff. That being said I think k&n is awesome for the right application but not for the l5p unless they offer an oil less filter like s&b ( I have not done research so they might) im just saying oil in the intake is your enemy
That pcv puts in a 1000x more oil into the turbo than any oiled filter could ever dream of.
 

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I have a buddy that owns a diesel shop and he says he has replaced more turbos because of oil filters because people oil them too much and it gets on the turbine and throws it off balance and eats up the bearings. That to me was enough to say ok dry filters is key lol.
I have rebuilt quite a few turbos from Duramax to Porsche, some with dry, some with oiled and I have never seen the condition your buddy speaks of that were caused by air filters. Any oil in the system will most likely be black in a Duramax and come from the EGR-PVC , NOT the air filter. I personally run a K&N on my LBZ with no issues in 410,000 miles. Consider all the over the road trucks that run an oil bath that have turbos, The OTR manufacturers certainly would not specify oil bath on million mile trucks if it would cause an issue. I would agree with your friend that quite often K&N 's are over oiled, seen that myself but I have not seen any imbalance issues from that.
 

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do a little reading on K&N filters before you decide to stick with that filter. DIRT in your motor! I watched a video on here a couple of days ago. Including that video, I have never seen a test where K&N wasn't DEAD LAST in filtering out dirt when compared to normal paper type filters.
Iit is hard to improve on the factory filter. Id try and return the setup for a refund ifI were you . Buy an extra load of beer instead
 
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Dont only look at the peak numbers tho - you need to look at the whole powerband to really see it. Just be prepared for some serious lashings from the Banks haters on here. Personally, with my L5P, i have the Derringer and PedalMonster and swear by it. To each their own
What's wrong with that Banks I dash just wondering.
 

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2017 GMC Denali 2500HD, 3.5" Rough Country Lift, 305/55R20 Yokohama Geolandar A/T
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What's wrong with that Banks I dash just wondering.
Not one thing wrong with the Banks iDash. It's a monitor that does a good job.

Banks have gotten a bad rap on here previously because they make a "canned" tuner and not "custom" tuning.
 

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This is the filter shootout mentioned earlier. Good comparison but I don’t like the way he did the small particle test. I’ve ran K&N Filters on both our 4 Runners with NO issues and a slight increase in gas mileage. As long as you don’t over oil them they work great. I would not use them on a turbo engine thou.


 

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This is the filter shootout mentioned earlier. Good comparison but I don’t like the way he did the small particle test. I’ve ran K&N Filters on both our 4 Runners with NO issues and a slight increase in gas mileage. As long as you don’t over oil them they work great. I would not use them on a turbo engine thou.



Below is another test done to ISO standards. Story behind this one is back in 2002, shortly after I bought this truck I was about to order a K&N filter for it because I'd heard good things about them. I was looking for a place to order / buy a K&N from so I did a google search. I think it was the first link that came up, but it was the original web page that the report was published on. After reading the report and looking at the graphs, there was absolutely NO WAY I was going to put a K&N on my brand new truck.

As an aside, I have a cousin that bought a Ford excursion with the 7.3 PS. He still owns it as far as I know but about 3 years ago (~300,000 miles), his truck wouldn't start. He had it towed to the Ford dealer. The mechanic told him that the reason it wouldn't start was because the injection system uses oil pressure to fire the injectors and his motor didn't have enough oil pressure to fire them. He then told my cousin that this was probably due to him running a K&N filter. I never knew he was running that filter in his Excursion or I'd have sent him a link to the test results I mentioned above. I also have no clue if 7.3s use oil pressure to fire injectors but am just taking the mechanic's word for it. I do know that 300k miles is nothing for a 7.3 PS.

Anyway, I'm sure this has been posted on this site many times in the past (it's been around a LONG time) but this guy tested many different filters and did multiple tests (unrestricted flow, restricted flow, filtering ability and such) and in damn near EVERY category, the K&N came up last. It also happened to be done with Duramax air filters which is why it came up in my google search for a Duramax K&N filter. The link below is not the original page where I found the report but apparently someone thought highly enough of the test and report that they saved it as screen shots and reposted it. The video posted above is just confirmation of what this guy posted ~19 years ago.

 

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Below is another test done to ISO standards. Story behind this one is back in 2002, shortly after I bought this truck I was about to order a K&N filter for it because I'd heard good things about them. I was looking for a place to order / buy a K&N from so I did a google search. I think it was the first link that came up, but it was the original web page that the report was published on. After reading the report and looking at the graphs, there was absolutely NO WAY I was going to put a K&N on my brand new truck.

As an aside, I have a cousin that bought a Ford excursion with the 7.3 PS. He still owns it as far as I know but about 3 years ago (~300,000 miles), his truck wouldn't start. He had it towed to the Ford dealer. The mechanic told him that the reason it wouldn't start was because the injection system uses oil pressure to fire the injectors and his motor didn't have enough oil pressure to fire them. He then told my cousin that this was probably due to him running a K&N filter. I never knew he was running that filter in his Excursion or I'd have sent him a link to the test results I mentioned above. I also have no clue if 7.3s use oil pressure to fire injectors but am just taking the mechanic's word for it. I do know that 300k miles is nothing for a 7.3 PS.

Anyway, I'm sure this has been posted on this site many times in the past (it's been around a LONG time) but this guy tested many different filters and did multiple tests (unrestricted flow, restricted flow, filtering ability and such) and in damn near EVERY category, the K&N came up last. It also happened to be done with Duramax air filters which is why it came up in my google search for a Duramax K&N filter. The link below is not the original page where I found the report but apparently someone thought highly enough of the test and report that they saved it as screen shots and reposted it. The video posted above is just confirmation of what this guy posted ~19 years ago.

7.3 are heui injected, and yes in short it uses oil pressure to fire the injectors. I have no idea how a k&n correlates with the injection system though?

I am not pro k&n, never ran one, just don’t know how that mechanic blamed his injectors on a k&n
 

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I think the correlation was that the k&n filter let in too much dirt, that ended up wearing out his oil pump.
 

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The guy just sounded like a K&N hater. I'd come a lot nearer thinking the 7.3 had developed high pressure oil system leaks. That was damn sure the case on most 6.0's which was a similar system, just much more problematic than the 7.3.
 
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