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Air Filter and Cars That Run Rich #4707138
03/26/18 06:17 AM
03/26/18 06:17 AM
Joined: Apr 2017
Posts: 414
Mississippi
Speak2Mountain Offline OP
Speak2Mountain  Offline OP
Joined: Apr 2017
Posts: 414
Mississippi
THEORETICALLY Speaking: Would a higher flow air filter (K&N/S&B) do more to prevent running rich than a lower flow/higher capture filter?

Theoretically speaking.....

Re: Air Filter and Cars That Run Rich [Re: Speak2Mountain] #4707143
03/26/18 06:23 AM
03/26/18 06:23 AM
Joined: Oct 2011
Posts: 2,986
Chicago, IL
Brybo86 Offline
Brybo86  Offline
Joined: Oct 2011
Posts: 2,986
Chicago, IL
Sure in an old carbed engine.

In a modern car I would be looking at something else as the ecu controls all the fuel.

Mb dirty throttle plate?


08 Honda Accord EX-L 2.4L M1 EP 0w20 145k
01 Kymco People 50
95 Lexus LS400 M1 AFE 0w30 193k
95 Yamaha Jog
Re: Air Filter and Cars That Run Rich [Re: Speak2Mountain] #4707197
03/26/18 07:43 AM
03/26/18 07:43 AM
Joined: Jul 2011
Posts: 260
SE Michigan
MichiganMadMan Offline
MichiganMadMan  Offline
Joined: Jul 2011
Posts: 260
SE Michigan
As previously stated: With a carburetor air filter restriction matters.

With a modern fuel injected car, it won't run rich. I bought a Chevrolet Aveo5 recently that had been neglected by all previous owners. The screws that held the lid of the airbox on were rusted solid indicating nobody had been in there in a long while. When I tried to hulk them out, the metal insert tore out of the lower half rather than releasing the screw.
The air filter was...horrific. First I poured the sand and gravel out of the airbox, then I plucked the grass and leaves out. The filter was nearly completely blocked (I was trying to figure out why it had 25 hp, instead of the usual 35..).
When I installed a new airbox with a new filter, I about did a burnout.

Fuel economy was unchanged, the O2 sensor was switching before and continued to do so after. Computers are really good at adjusting for variances in environment.

A note: Cars running speed-density fuel injection are more prone to "get lost" with their fueling than cars running a MAF (where they measure the actual air going into the engine).


2015 Chevrolet Impala
2008 Subaru Impreza STI
2004 Suzuki Hayabusa
1987 Honda VFR700F2
2011 Jonsered 2188 Chainsaw-The Judge.
Re: Air Filter and Cars That Run Rich [Re: Speak2Mountain] #4707198
03/26/18 07:44 AM
03/26/18 07:44 AM
Joined: Dec 2014
Posts: 211
USA
dbias Offline
dbias  Offline
Joined: Dec 2014
Posts: 211
USA
MAF sensor should be metering air and the ecu sends fuel appropriately. Looking at short term and long term fuel trims is more useful in identifying rich and lean conditions.


2011 VW JETTA Castrol Edge 0W-40
2012 FORD TRANSIT CONNECT Castrol Edge 5W-20
2016 HONDA CIVIC COUPE Castrol Edge 0W-20
2017 AUDI A4 Ravenol SSL 0W-40
Re: Air Filter and Cars That Run Rich [Re: Speak2Mountain] #4707259
03/26/18 08:43 AM
03/26/18 08:43 AM
Joined: May 2009
Posts: 12,248
N.H, U.S.A.
ARCOgraphite Offline
ARCOgraphite  Offline
Joined: May 2009
Posts: 12,248
N.H, U.S.A.
Dirty filter will throttle the engine. My car runs rich - black tail pipe - I blame it on MAF MAP or even low octane fuel - it runs cleaner if I add 30% 93 octane and the car has MUCh more low end grunt.

So look to a too tight K sensor if everything else is OK.

Give the MAF a CRC Cleaner shower to start - make sure airbox is tight and no rodents chewed any vacuum control lines.

also if you drive too easy all the time the chamber and cat will be crusty.

Last edited by ARCOgraphite; 03/26/18 08:44 AM.

2014 Nissan Rogue S CVT, OC#9 41392mi-QSUD10W30 + M110A CHAMP Filter; 2017 Subaru Crosstrek CVT OC#2 ?? mi-SOA/Idemitsu 0w20 + SOA Filter
Re: Air Filter and Cars That Run Rich [Re: Speak2Mountain] #4707272
03/26/18 08:54 AM
03/26/18 08:54 AM
Joined: Sep 2007
Posts: 8,598
Florida
artificialist Offline
artificialist  Offline
Joined: Sep 2007
Posts: 8,598
Florida
Not only does it cause carb engines to run rich, it can also cause a non-computerized diesel engine to make more black smoke.


2010 Lancer Ralliart Sportback
Re: Air Filter and Cars That Run Rich [Re: Speak2Mountain] #4707335
03/26/18 10:01 AM
03/26/18 10:01 AM
Joined: Dec 2013
Posts: 3,989
Manchester, England
Olas Offline
Olas  Offline
Joined: Dec 2013
Posts: 3,989
Manchester, England
It's entirely dependent on control systems.

Anything with maf/map/lambda sensors should maintain afr regardless of pressure drop across the filter.

Anything open loop injection ie mechanical-pump diesels or also some of the earliest injected petrol engines will get richer as the filter gets obstructed.

Carbureted engines will maintain afr up to a point because the plugged filter slows the airflow across the carburettor pulling less fuel, but after that given point it just becomes a bolt-on choke.

Last edited by Olas; 03/26/18 10:03 AM.

Cable ties should hold it
Re: Air Filter and Cars That Run Rich [Re: Speak2Mountain] #4707340
03/26/18 10:04 AM
03/26/18 10:04 AM
Joined: Oct 2014
Posts: 12,030
Idaho
CT8 Online content
CT8  Online Content
Joined: Oct 2014
Posts: 12,030
Idaho
Originally Posted By: Speak2Mountain
THEORETICALLY Speaking: Would a higher flow air filter (K&N/S&B) do more to prevent running rich than a lower flow/higher capture filter?

Theoretically speaking.....

it depends on why the engine runs rich.


2015 Ford F150 2.7
2018 Ford F350 6.2
Re: Air Filter and Cars That Run Rich [Re: MichiganMadMan] #4707354
03/26/18 10:13 AM
03/26/18 10:13 AM
Joined: Oct 2012
Posts: 4,779
Taiwan
Ducked Offline
Ducked  Offline
Joined: Oct 2012
Posts: 4,779
Taiwan
Originally Posted By: Speak2Mountain
THEORETICALLY Speaking: Would a higher flow air filter (K&N/S&B) do more to prevent running rich than a lower flow/higher capture filter?

Theoretically speaking.....


Theoretically speaking, no. Neither air filter is designed to "prevent running rich" .

Even a carbed engine is built and tuned to deliver the correct mixture with whatever restriction the OEM filter applies, so IF there was an effect at all, the higher flow filter would run lean, rather than the OEM filter running rich.

Practically speaking, even on a carbed engine, there is negligable effect until the filter is heavily clagged, at least according to the most readily available study.

https://www.fueleconomy.gov/feg/pdfs/Air_Filter_Effects_02_26_2009.pdf

Originally Posted By: MichiganMadMan
As previously stated: With a carburetor air filter restriction matters.


As previously stated, no it doesn't.

At least not according to the above study. (I think they only tested one carbed car).

Severe air filter clogging matters, although to get more than a 2% drop in fuel economy they had to add so many shop towels that drivability was severely impacted and the filter parially collapsed.

Designed air filter restriction has negligable effect.

Recently I rigged a water manometer as a restriction gauge and decoker. The filter has been on the car since I bought it (about 7 years IIRC) in dusty Taiwan and the restriction was not measurable. I had to add paper towel and toilet paper to the filter to get the gauge/decoker to work.

Last edited by Ducked; 03/26/18 10:35 AM.
Re: Air Filter and Cars That Run Rich [Re: Brybo86] #4707400
03/26/18 11:02 AM
03/26/18 11:02 AM
Joined: Jan 2013
Posts: 1,920
Texas
WyrTwister Offline
WyrTwister  Offline
Joined: Jan 2013
Posts: 1,920
Texas
Originally Posted By: Brybo86
Sure in an old carbed engine.

In a modern car I would be looking at something else as the ecu controls all the fuel.

Mb dirty throttle plate?


Or a messed up sensor , like may be a coolant temp sensor . For example .


Wyr
God bless
Re: Air Filter and Cars That Run Rich [Re: Speak2Mountain] #4707412
03/26/18 11:11 AM
03/26/18 11:11 AM
Joined: May 2016
Posts: 718
Canada
i_hate_autofraud Offline
i_hate_autofraud  Offline
Joined: May 2016
Posts: 718
Canada


A high flow air filter, K&N, etc that needs filter oil pretreat can be a problem on any
late model engine with a MAF sensor, trace amounts of oil migrate into the MAF and dirt sticks to
the MAF element inside, then sets codes, this takes a while, maybe a year or so.

The codes set last time were related to fuel injection related, not directly pointed at a MAF
problem. The easier thing was to remove and clean the (GM) MAF with a spray and dry it out with
a warm hair dryer. If the MAF is powered up with ANY cleaner inside, it can blow the hot-wire element
since they are super thin, when cleaner finally flashes off, the wire can pop. I cleared the codes
and they never came back.

If you clean and oil your re-usable K&N and add a bit extra oil it may filter better, but use it
on a car with a carb not a MAF sensor! Don't get me wrong I like the K&N and the cleaning kit, it works well!
Just not worth the hassle when it risks the MAF sensor!

I noticed the duct behind the K&N filter had signs of dirt that got thru. I washed and oiled the K&N
filter and put it back in the box to sell off with the cleaner kit. I'm back to a good paper pleated filter!

Re: Air Filter and Cars That Run Rich [Re: Speak2Mountain] #4707505
03/26/18 01:04 PM
03/26/18 01:04 PM
Joined: Feb 2011
Posts: 6,725
Hudson, NH
LeakySeals Offline
LeakySeals  Offline
Joined: Feb 2011
Posts: 6,725
Hudson, NH
Originally Posted By: Speak2Mountain
THEORETICALLY Speaking: Would a higher flow air filter (K&N/S&B) do more to prevent running rich than a lower flow/higher capture filter?

Theoretically speaking.....

Theoretically speaking the MAF would sense more air flow with the K&N. Report that to the ECU which would add fuel to keep the mixture correct. So if anything it would be richer. Maybe.


06 Escalade 6.0L LQ9 AWD 165k M1 5w30
03 Maxima 3.5L POS 152k ST HM 10w30
Re: Air Filter and Cars That Run Rich [Re: Speak2Mountain] #4707530
03/26/18 01:41 PM
03/26/18 01:41 PM
Joined: Dec 2009
Posts: 665
Wash, DC
circuitsmith Offline
circuitsmith  Offline
Joined: Dec 2009
Posts: 665
Wash, DC
The more recent carburetors float bowl and air jets are vented to downstream of the air filter, so filter restriction is largely compensated for.
This is evidenced in the fueleconomy.gov paper linked above.

Last edited by circuitsmith; 03/26/18 01:41 PM.

2017 Hyundai Tucson SE FWD, 5000mi/12mo OCI
Re: Air Filter and Cars That Run Rich [Re: Speak2Mountain] #4707652
03/26/18 04:02 PM
03/26/18 04:02 PM
Joined: Jul 2003
Posts: 4,813
New Zealand
Silk Offline
Silk  Offline
Joined: Jul 2003
Posts: 4,813
New Zealand
More recent as in a long, long time ago. Atmosphere vented carbs will run rich with a blocked filter by the late '60's, early '70's float chambers were vented to the airhorn, and won't go rich with a restricted air filter.


1987 BMW R65 - Penrite V Twin 20/50
2005 Nissan Expert - Gulf Western 10W-40
1996 Volvo T5 - Penrite HPR15 - 15W-60. Ryco syntec filter.
Re: Air Filter and Cars That Run Rich [Re: Speak2Mountain] #4709416
03/28/18 10:16 AM
03/28/18 10:16 AM
Joined: May 2016
Posts: 718
Canada
i_hate_autofraud Offline
i_hate_autofraud  Offline
Joined: May 2016
Posts: 718
Canada


K&N "may" allow more air / power, but you'd have to redline the engine to see the improvement either on the track or
dyno.

City / hiway driving at legal speeds at part throttle would see no difference - except the "confirmation bias"
of an owner who puts in a K&N and then fools themselves into believing there's more power at 2,000 rpms!


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