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Unread 05-14-2013, 07:23 PM   #16
rm2001wj
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What some of you are missing is that the PCM, using O2 sensor signals, pretty much keeps the air/fuel (A/F) mixture at the stoichiometric ratio of 14.7:1 when the engine is running in closed loop mode. By far, closed loop mode (which means partial throttle operation) is what contributes to fuel efficiency. If the air filter is partially clogged, less air will enter unless more accelerator pedal is used. In any case, fuel injected will still match the air intake and mpg won't be affected. Keep in mind that it is the throttle position that determines the air intake rate during partial throttle operation, and the condition of the air filter has little to do with it until the filter is so clogged that almost no air can get into the engine even with the throttle wide open.

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Unread 05-14-2013, 09:14 PM   #17
lazyWJ
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Quote:
Originally Posted by alfaitalia View Post
Surely you have answered your own question as far as the dirty air filter is concerned. Let's assume that you are right that a dirty filter only affects performance and not mph (although all my experience tells me otherwise) then your performance will decrease..... so to go as fast as you would with a clean filter you will have to give it more throttle and therefore you WILL use more gas. The only way you could be right would be if you could drive at exactly the same throttle opening and just accepted the reduction in speed..... something that, in the real world is about impossible to do....you would just push the throttle further down to over come the lack of power and therefore burn more fuel. As I always say "there are lies, damn lies and then there are statistics". So don't believe every lab report will turn out like that in the real world.

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Incorrect. Wildly so. Instead of believing independent lab tests (and common sense), you choose to believe propaganda from air filter companies. Hmmm....

Quote:
Originally Posted by rm2001wj View Post
What some of you are missing is that the PCM, using O2 sensor signals, pretty much keeps the air/fuel (A/F) mixture at the stoichiometric ratio of 14.7:1 when the engine is running in closed loop mode. By far, closed loop mode (which means partial throttle operation) is what contributes to fuel efficiency. If the air filter is partially clogged, less air will enter unless more accelerator pedal is used. In any case, fuel injected will still match the air intake and mpg won't be affected. Keep in mind that it is the throttle position that determines the air intake rate during partial throttle operation, and the condition of the air filter has little to do with it until the filter is so clogged that almost no air can get into the engine even with the throttle wide open.
Correct, thank you for explaining it so that hopefully everyone can understand it.
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Unread 05-15-2013, 06:24 AM   #18
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Originally Posted by lazyWJ View Post

Incorrect. Wildly so. Instead of believing independent lab tests (and common sense), you choose to believe propaganda from air filter companies. Hmmm....

Correct, thank you for explaining it so that hopefully everyone can understand it.
Oops....double post.
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Unread 05-15-2013, 06:34 AM   #19
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Originally Posted by lazyWJ View Post

Incorrect. Wildly so. Instead of believing independent lab testsk (and common sense), you choose to believe propaganda from air filter companies. Hmmm....

Correct, thank you for explaining it so that hopefully everyone can understand it.
I don't believe the air filter companies and run a std paper filter. I think the common sense would tell you that a clean filter will give better has mileage.....not to mention all the mpg threads on here that claim improvements with a clean filter. I notice the way you ignored the bit about having to use more throttle to get the same power. Also you would lose mpg from the effort of pulling air through a dirty filter. I along with countless others have gained mpg from a new filter so who is ignoring common sense now.


As for the other post ...well a bit of knowledge is a dangerous thing. Closed loop is only relevant at constant throttle settings and idle....not a large percentage of driving in the real world.

By the way two minutes on Google finds 50 other pieces of "research" that agrees with me. Remember that for each expert there is an equal and opposite expert!

Put an old filter in and see for yourself.
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Unread 05-15-2013, 10:22 AM   #20
rm2001wj
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Quote:
Originally Posted by alfaitalia View Post
I don't believe the air filter companies and run a std paper filter. I think the common sense would tell you that a clean filter will give better has mileage.....not to mention all the mpg threads on here that claim improvements with a clean filter. I notice the way you ignored the bit about having to use more throttle to get the same power. Also you would lose mpg from the effort of pulling air through a dirty filter. I along with countless others have gained mpg from a new filter so who is ignoring common sense now.


As for the other post ...well a bit of knowledge is a dangerous thing. Closed loop is only relevant at constant throttle settings and idle....not a large percentage of driving in the real world.

By the way two minutes on Google finds 50 other pieces of "research" that agrees with me. Remember that for each expert there is an equal and opposite expert!

Put an old filter in and see for yourself.
Here is a link to actual research as opposed to internet chatter and myths. http://www.fueleconomy.gov/feg/pdfs/...02_26_2009.pdf If you can understand the article, you will also get an idea of what procedure must be followed to actually measure the effect of a single engine modification on fuel efficiency.

BTW, you are very wrong about you said about closed loop operation. If you were correct, most driving would be done in open loop in which case O2 sensor signals are completely ignored by the PCM. The major point of having various sensors providing feedback to the PCM (that is what closed loop means) is to enable the engine to burn fuel efficiently and completely so that exhaust emissions are minimized. That process also leads to best mpg as far as our engine operation is concerned.

A common mistake many people make about throttle position is due a belief that the throttle somehow injects more fuel as it is opened. That is completely wrong. Opening the throttle more will only allow more air into the engine. The various sensors such as MAP, IAT, engine speed, and etc. enable the PCM to judge the mass air flow rate and control the injectors correctly. If the PCM is a little off, the O2 sensor signals let the PCM make corrections. With this scheme, while a dirty air filter might reduce air flow and require a wider throttle opening to get the previous air flow, the PCM knows what the air flow is and matches it with the correct fuel flow.

Here's a challenge for you. Spend some time on the K&N Filter website and see if you can find anything where they say a K&N filter or CAI will increase mpg. Despite testimonials that claim better mpg, K&N knows that it just won't happen.

Finally, when someone appeals to "common sense" as an authority, it means that they do not have any rational explanation.
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Unread 05-15-2013, 11:50 AM   #21
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Quote:
Originally Posted by lazyWJ View Post
U joints eating 2mpg? Do you know how much energy has to be converted to heat in a u joint to account for 2 mpg? Some egghead could actually calculate that (amount of energy in a gallon of fuel, number of miles, joules, calories and all that stuff. It's measurable by someone smarter than I am) That's a lot of energy, and a lot of heat. Unless it's converting the energy into something else, electricity perhaps? And I'm dying to hear how one picks up 12mpg, nearly halving the fuel required to move the vehicle.
Perhaps you need to switch to decaf?
A bad u-joint can eat 2 mpg. I don't have any scientific studies to back that up, nor am I going to sit here and calculate the energy converted to heat in such an instance. It happened to me, and it happened to my co-worker on his Avalanche. The U-joints were the ONLY thing changed, and the difference was immediate in both cases. That's enough for me. If it's not enough for you, I don't really care.
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Unread 05-15-2013, 08:21 PM   #22
henrygeorge
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perhaps the computer compensates by allowing the engine run a little rich if the air filter is clogged. could be something unique to the wj i6. who knows. all i know is that something fixed my mpg and it didn't seem to be fixed until i ran it with the new air filter. i did do most of the other things a couple of days before the air filter.
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Unread 05-21-2013, 09:08 AM   #23
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I have only experienced that a clean air filter and new fuel filter increasing mpg on my wj with the serial number I bought. These finding may or may not work with YOUR serial number wj...
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Unread 05-21-2013, 03:33 PM   #24
henrygeorge
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i did add a little bit of seafoam to the engine, which probably increased the mpg, but i didn't see the increase until i replaced the air filter. i did go ahead and change the oil and filter after 200 miles with 5w-30 valvoline. the oil was fairly clean but old and thick. my oil pressure dropped to the 40-50 psi range when i put the new oil in it, which i believe is more normal than the 60 psi i originally had. the epa web site does say that old oil and the wrong viscosity will significantly impact your mpg in the range that i corrected it.
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Unread 05-21-2013, 08:48 PM   #25
OffroadOran
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id be lucky to get good gas mileage on mine. my overhead says 12.5 mpg average with all city but i drive city about 97% of the time and rarely go on the highway. Like others have said, i think the overhead display lies because i feel like i definitely get more than that even driving through the congested city route i do every day
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Unread 05-22-2013, 10:49 AM   #26
02grandy
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to change all four O2 sensors with dealer sensors $$$$$ oh boy lol... do you go with dealer mopar or NGK/NTK? i doubt they are densos. never looked up close
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Unread 05-22-2013, 01:39 PM   #27
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I dont care about mpg, I care about spg
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Unread 05-22-2013, 03:46 PM   #28
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So we should never replace our air filters? If my air filter is 20% blocked do I still get the same MPG? How about 50% blocked? 75% blocked?.....90% blocked?

An engine is a pump. Nothing more, nothing less. It pumps in air, makes explosions, and pumps out exhaust. Anything that can be done to make it pump more "easily" ("efficiently") will improve it's "performance", and in this case I will define "performance" as how far it will make my Jeep move on a gallon of fuel.

Air filters add resistance to the air being pumped into the engine. If I have a dirty air filter, it's harder for the engine to pump in its air, and it takes more of the engine's output power to pump in the air, so that's less output power that can go to moving the Jeep.

I'm no genius, by any means, but this is how I view it.

Will you say that clogged cats are ok too? Or mandrel-bent exhausts being no better than rough bend pipes? It all helps the "pump" pump more easily, in OR out.

No matter, really. If you want to run around with a dirty air filter, it's your Jeep.

Just my $0.02
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Unread 05-22-2013, 04:15 PM   #29
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Unread 08-20-2013, 07:06 PM   #30
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This closed loop thing!! ??? Now I run LPG on mine so it tends to muddy the measurements.
But as far as I have found there is not a MAF sensor in the air intake line just a vacuum sensor on the manifold and a TPS, I haven't counted the O2 sensors but I know of at least the one in the exhaust which should balance the burn mixture. But. And it's a bit but.
You may be aware that in the management electrics PCM are a couple of fuel trims. Some temporary some long term which need a dealer of proficient garage black box to adjust via the obd2 (thingy) port.

Now I understand the logic if the filter is dirty air flow is reduced and to get the same quantity of air into the engine the throttle needs to be opened more. This increases the TPS reading and is balanced by the manifold vacuum reading, so clogged filter would affect these readings and change the placing on the fuel map that the PCM reads, this would affect mpg and alter the fuel trim which would change the O2 range that is fed back.

This closed loop is therefor not a constant output and effects mpg.

Which brings me to my question and why I looked in to this thread..
Any one know how to fool the fuel trims because with the LPG fitted when I changed the battery they reset and I'm running rich again after a costly session at my garage sorting out the trims.
I know it's rich because it failed the CO2 test on petrol but passes on LPG.
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