philiptompkins

iTrader: (4)

Allright, I've read on here numerous times about how the O2 sensor does next to nothing, maybe 1 or 2 mpg increse ect. Well I had mine disconnected for about 6 months and a friend (with an air impact wrench) helped me change mine. I just got back from driving it nearly 500 miles (Houston to New Ibearia LA). Well I did not notice any signifacant power increases BUT my mpg was imporved by at least 25-30%. I don't have any scientific numbers but I used to burn over 3/4 of a tank each way, this time i barley burned over a half tank.

Cliff Notes: Change / plug in your O2 sensor to signifacantly increase mpg.

My car: S5 N/A

ultrataco

iTrader: (2)

wow, i wish i could reconnect my O2 sensor.

SureShot

In all normal cruising, the O2 sensor is monitored by the ECU to automatically lean the AFR to a perfect 14.7.

Without it, the ECU thinks you're about to floor it, so it's mapped to the rich side.

Even with an S-AFC or a stand alone, you're only controlling medium & full throttle acceleration.
Cruise is still closed loop with the O2 sensor, and deceleration is fuel cut.

philiptompkins

iTrader: (4)

Thanks, I don't really undersatnd all the thechnical reasons. I just know it helped alot, and hopefully it can help other rx-ers

iSP33D-for-J3SUS

Where is the 02 Sensor located anyway?

iSP33D-for-J3SUS

spot_skater

Stock exhaust? Near the stock exhaust manifold.

DeclareYrWar

yeah i changed mine recently and i went from 16mpg on the highway all the way up to 25 this time around (just took a trip to atlanta). both times i calculated it i was setting the cruise control at 70 the whole trip (most of the time anyways haha)

mrtiddles

Well yeah, but don't these cars get about 25-30% increase in MPG on highway driving versus city driving?

wildfc3s

hmm pretty good info

NZConvertible

Sorry to burst your bubble, but unless you previously had black smoke pouring out the tailpipe, that's just not possible. To get a 25-30% reduction in fuel consumption (assuming the driving conditions were near identical in both trips), you would have needed to be injecting 33-43% more fuel before than you were after. That's obviously ridiculous and simply didn't happen.

Closed loop (where the ECU uses the O2 sensor) only occurs during cruising conditions, so since you were doing a long distance cruise you would see the best possible improvement from having a working O2 sensor. If you're lucky this gain might be as much as 10%. When I installed a new sensor after not having one for ~6 months my average fuel consumption dropped by 4-5% (which is less than 1mpg). That's based on actual measured and calculated figures over a few months before and after, on a daily-driven car that sees a wide variety of driving conditions, including closed-loop conditions.

And that's the problem. You're using a notoriously innacurate gauge that doesn't display the actual amount of fuel in the tank, especially in the middle of it's range. Without real numbers (miles travelled, gallons consumed) your claims are literally unbelievable.

90WhiteVrt

I reconnected my O2 sensor and went front 19 mpg on the highway to 23, so yes, it does make a significant difference. Although I do miss the loud explosions that would echo from my exhaust every time i switched gears...

monkhommey

thanks NZConvertible! for shuting that guy down! just one question tho. are all of your 12,822 post just as bitchy? because i didnt sign up for to this forum to hear some jackass walkin and try to make himself feel all powerful by snaping at someone over fuel economy. all the guy said was he obvserved a decrease in fuel consumption. he even admitted that he didnt have accurate numbers. so freakin what! and just curious.. where did you get the 33-43% more fuel thing? are you saying that if you reduce the amount of fuel being injected by 33-43% that you would only be reducing the amount of fuel being used by 25-30%? so where does the other 8-13% go? i might just be really dumb or something but it seems to me that the there is a direct relationship between the fuel being injected into an engine and the fuel being consumed by the engine.....

you dont know if how much fuel efficeincy he gained. maybe one way was more up hill then the other time.. or maybe he had to coast more with the engine at idle then before.. or maybe he had a different octane gas or maybe the wind was at his back and he was riding the *** of a semi-truck... i would honestly believe that guy over you.. just because he is a little more humble..

i may be out of line but i just get tired of people being bitchy and snappy.. we are all here to post our ideas, or questions, and suggestions. its not benificial to post a comment and have someone reem you for it..

comradegiant

It wasn't bitchy at all, it was stating facts.

If you come in stating that "I don't have any scientific numbers", you have to expect that someone is going to do the math.

slo

iTrader: (1)

What he is saying is that if with closed loop its running stoich at 14.7-1 and you increase fuel by lets say 37% then your new ratio is approx 9.3-1 in other words the car would run like **** and not for very long spew fuel smoke and foul plugs.

Mechanic

Some people are on the forums just to degrade others... and others claims that they dont, and are stating fact, but either their vocabulary is very limited, or he just dont know how to rephrase it to make it more friendly. No one is right on this one.

Other than that...

I don't about rx7's (I run a carb), but my 240sx sure as hell saved me gas money.

With old 02sensor in the 240sx for 60-65 miles of highway crusing going to stony brook, shifting at a average of 3500rpm, or as close as possible if conditions permit, and crusing at 5th gear around 2500 rpm, at 65 miles (give or take a few, some times gas stations arent for another 3-5 miles extra travel for a 10 cent difference in price) went with a avg of 3.02 (give or take .12) gallons. This equals an average of 21.52miles per gallon.
Tested on 5 trips.
After I replaced the 02 sensor (by the manifold) , I've notice a gain in gas milage, wow. For the same five trips, for 65 miles going to the same place (give or take a few miles, depending on cheapest gas station). Also performing as close as I can to replicate driving style, that 65 miles only cost me average of 2.41 gallons (add or take .13) now take that and do the math, and I get a nice 26.97 miles per gallon.

With that said and tested, i'd say it makes a good difference.
I never tested city driving, but with the new sensor, I seem to be averaging just about 22 mpg so, i think it works... aside from that I sold the car, so doesnt matter what milage i was getting, im getting 10 mpg right now.

I can be wrong, i decided to test this because gas prices were starting to rise. and i got my mpg of driving style cruise i get 11.77 mpg mix i get 9.83 mpg and 7k shifts i get about 5 mpg if im lucky...

monkhommey

comradegiant:

"Sorry to burst your bubble, but unless you previously had black smoke pouring out the tailpipe, that's just not possible." & "That's obviously ridiculous and simply didn't happen." & "your claims are literally unbelievable."

i apologize those quotes are rather polite.

and he didnt do "the math" the only math i see in his post is that he figured out that 4-5% of his fuel economy was less then 1 mpg.


NZ_87_TURBO :

really it must be the case..


but.. there is no math to be done.. the guy said he used a quarter tank of gas less after replaceing the o2 sensor on the same drive.. 2 other people on this thread report the same thing.. why do you think that you have to do stoichiometry? first off fuel economy and fuel consumption are two different things..

slo:

i calculated the afr would be 10.73 to 1 if you increase the fuel injected by 37%. if i did that calc right then thats a little different then 9.3 to 1. and thats with 37% addidtional fuel being injected. the guy said his fuel ECONOMY increased by 25-30%, and that was a very rough number... now if you assume that that means that the fuel being consumed by the engine was reduce by 20-30% wich it doesnt.. then the afr would have been 11.3-12.25 to 1..

i dont see how it is possible to say that if you reduce the amount of fuel by being injected into the engine by 43% then you ony reduce the amount of fuel being consumed by 30%... that just doesnt make sense to me..

ol yeah and NZConvertible has a S4 turbo car.. philiptompkins has a S5 na car.. just because nz didnt have similar results doesnt make him right.. now does it..

all im sayin is dont jump into a thread and down the original poster because you think your right and then throw in a bunch of numbers and state that your right and then say that you proved it for your own situation which is very much different then someone elses and then tell them that "your claims are literally unbelievable." just so you can be right.. nothin he posted was really of any help to anyone..

DeclareYrWar: if you have a problem with something i post.. tell me what it is. other wise i will remain really dumb...

slo

iTrader: (1)

I droped out of HS before calc, but your right on the math I did the calculation in my head. But with that ratio the car would still smoke and foul plugs.

NZConvertible

Mostly yes. Feel free to search for them and have a read.

That's quite an imagination you've got there. How's the view from up on that soapbox?

And that's the problem. He guessed instead, and his guesses were simply not believable to anyone who understands how closed-loop works.

It's high school maths. A 25% reduction in fuel used would mean the amount being used now is 75% or 0.75 of what was being used before. To go backwards to get the original figure you invert this. 1/0.75 = 1.33 or 33% more. Get it?

And neither does he. But at least I understand what closed-loop actually does, and have performed far more accurate before-and-after testing on my own car, so I have a much better idea of what can be expected than he does.

And all of those things would make any results inaccurate and hence useless. It's perfectly normal to get different results on a return trip without making any changes, simply because of different driving conditions.

I guess I won't bother answering any of your questions then.

Neither is it beneficial to post misinformation, untruths, unsubstantiated guesses and just plain ol' BS, but people still do it. This is a technical forum, and it's emphasis should always be on factual information. Anybody who posts incorrect or misleading info should expect to be called on it. If that bothers really bothers you so much, nobody's forcing you to be here...

And that "quarter of a tank" was based on reading the stock fuel gauge, which is completely useless for measuring the actual amount of fuel used.

I know you're just going to think this is me being bitchy again, but this shows you don't understand the subject matter well enough. Since we're talking about driving in mostly closed-loop conditions, you're suggesting that before fitting the O2 sensor his average AFR while cruising is 11.3-12.25:1, which is absolutely crazy. That's not far off what you'd aim for at peak power. The average cruise AFR should be well above that. There seems to be a common misunderstanding that outside of closed-loop the ECU just runs the engine bulk rich, which is completely wrong.

The effects of a working O2 sensor are the same for a turbo'd engine as they are for an NA one. Remember the turbo is doing very little in closed-loop conditions.

So what you're saying is anybody should feel free to come in here and make unrealistic claims results based on mostly guesswork, and that nobody has the right to call BS. Dude, get real...

philiptompkins

iTrader: (4)

I have the O2 sensor in the stock hole on the stock manifold. And about the black smoke, I just put new cats on 8 months ago and passed emissions so i'm not shure I would have seen black smoke anyway.

And to all the others: You may be right, like I said I do not understand how the computer works and what it does or doesent do with the O2 sensor. I was just sharing my personal expericance and trying to help other FC owners. Many of you hard-core tuners probably don't even care about fuel economy that much, I'm shure a few of you burn $50 in gas a week in your FC though (I know I do). Just trying to help. And the trips that I take that I used as a bench mark for highway fuel consumption are just about 200 miles each was on I-10 which is very flat.

Project88Turbo

iTrader: (22)

The stock fuel gauge is not accurate to say the least. On a trip from my new house to my old one (about 320 miles all highway) today these are the readings and corresponding mileage.

FULL - 0 miles
3/4 - 70 miles
1/2 - 150 miles
1/4 - 240 miles
empty - 350 miles
low fuel light - 360 miles

Refueled at 360 miles and it only took 14.1 gallons. 25.5 MPG and still another ~2.4 gallons in the tank, gauge pointing directly left. BTW, it is a 88 Turbo, and results were achieved @ 70-75 MPH constant.

Vince

NZConvertible

That doesn't make any difference. Overly rich mixtures make black or brown smoke whether the cat's there or not.

Don't take what I said personally, I'm just trying to make you realise the O2 sensor can't have such a huge effect on fuel consumption, and that you need to take proper measurements befoer you can make claims of such massive improvements. This applies to anything you do to your car.

Reconnecting your O2 sensor was still a good idea and I recommend anyone with an original or non-functional O2 sensor to replace it with a new one and make sure it works properly. Just because rotaries are naturally thirsty doesn't mean we shouldn't bother trying to make them more efficient.

Aaron Cake

iTrader: (1)

Thread cleaned. A lot of people here need to learn that just because someone contradicts what they are saying, DOES NOT MEAN that person is insulting them. Maybe it's because the median age here is so low that this happens, maybe it's because the general knowledge level is so low. Who knows. But there are a good number of people on this forum that KNOW WHAT THEY ARE TALKING ABOUT and have done their own research and experiments to prove it. These people spend a great deal of time correcting the constant stream of misinformation that is posted and can sometimes get a little frustrated when the same thing they have corrected 500 previous other times is posted yet again and then argued...