The Effect of Replacing O2 Sensors - Results

matreyia

Major
Apr 19, 2017
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335i e93
Full FBO and MHD Wedge Tune. Was getting super duper shitty gas mileage - we talking 12mpg...

Replaced all four o2 sensors and mileage shot back up like a rocket. Now 18-20 city and 23-24 highway.

This is with down pipes.

So if there is anyone who is wondering if changing o2 sensors after 100k miles will help your car even if it is tuned... it certainly helped mine and runs even smoother than before.

I kept asking many sources, mechanics, dealers etc about the effect of o2 sensors on mileage and none of them seemed to think it would matter if my original o2 sensors were working fine. But what they failed to take into account is that an o2 sensor may work and not throw codes, but it still might be in what is called "lazy". This is after the sensor loses efficiency and the DME has to compensate too much... that is what happened to my old set.

Just reporting results.
 

doublespaces

General of the Army
Oct 18, 2016
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Did you have just the stock o2's? I have the ADV sensors, but I haven't even looked/checked fuel economy... I know its bad.
 

doublespaces

General of the Army
Oct 18, 2016
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The ADV sensors are superior in a number of ways, but I won't go into that here. You've got me wondering what my mileage is now :)
 

matreyia

Major
Apr 19, 2017
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The ADV sensors are superior in a number of ways, but I won't go into that here. You've got me wondering what my mileage is now :)

One tank of gas on 93 octane was 170 miles.... now back to 350 miles mixed driving. And 425 highway.
 

langsbr

Captain
Apr 5, 2017
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A before and after comparison is just anecdotal. Do you have before and after logs? It would be interesting to see how the fuel trims changed.
 

matreyia

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Apr 19, 2017
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A before and after comparison is just anecdotal. Do you have before and after logs? It would be interesting to see how the fuel trims changed.

No logs. Was not interested. Just wanted better gas mileage and that is what I got. If this is useless to you then pay no attention.
 

langsbr

Captain
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LOL no need to be a tool about it. The problem is you have no idea why you got better gas mileage. But hey - good job being a part swapping monkey!
 
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langsbr

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Nothing offended me, but you came across poorly with the "If this is useless to you then pay no attention." I merely stated that it would have been interesting to see the quantifiable change that resulted in the increased mileage. That's how you learn things. You stated firmly that you are not, and thus you will remain ignorant and chase problems by swapping parts.
 
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matreyia

Major
Apr 19, 2017
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LOL no need to be a tool about it. The problem is you have no idea why you got better gas mileage. But hey - good job being a part swapping monkey!

What is the problem again? I had shitty gas mileage...replaced all replaceable parts recently and still got shitty gas mileage... I changed all o2 sensors and immediately experienced way better mileage which was what I was after.

So why do I need logs? It is obvious tgat the only thing different was the replacement of sensors.

So I am confused to why you concern yourself with logs.
 
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matreyia

Major
Apr 19, 2017
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Nothing offended me, but you came across poorly with the "If this is useless to you then pay no attention." I merely stated that it would have been interesting to see the quantifiable change that resulted in the increased mileage. That's how you learn things. You stated firmly that you are not, and thus you will remain ignorant and chase problems by swapping parts.


I remain ignorant and chase problems? Ok.. you have no idea what the situation is and this is your assessment.

I am going to just stop here because you are acting in the same arrogant manner as a couple of people commenting on my posts. You know not the full situation nor the person and you come in like you know things... dismissing this report as anecdotal, but you perceive my response to ignore the comment as me being a tool. And if I point out all the things that you do not see urself doing...we may waste much time and end up with nothing good.
 
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The Convert

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Part swapping monkey? Because I like to maintain my car perfectly?

Man you fuckers got some balls.
You yourself admitted to just replacing parts, with no data, to try and fix a problem. You were bound to get it right eventually. A diagnostician, or someone who was not a part swapping monkey, which is what most techs at dealerships are called nowadays, would have logged and done a root cause analysis rather than blindly throwing parts at a car.

But hey, even a blind squirrel occasionally finds a nut, right?
 
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matreyia

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Apr 19, 2017
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Se
Hence the part swapping monkey...
See how this is turning out? You come in dismissing a simple report as anecdotal... i reply to you and say just ignore it if it is not useful... you project your personhood and life view onto the reply... you call me a tool.... then I point this out and you have nothing to say or do except for vote down a comment.

Way to be a grown up.
 

matreyia

Major
Apr 19, 2017
1,737
678
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You yourself admitted to just replacing parts, with no data, to try and fix a problem. You were bound to get it right eventually. A diagnostician, or someone who was not a part swapping monkey, which is what most techs at dealerships are called nowadays, would have logged and done a root cause analysis rather than blindly throwing parts at a car.

But hey, even a blind squirrel occasionally finds a nut, right?

Yeah... I replaced almost every replaceable part... because they were all due. The fact that I saw no mileage improvement does not mean that gas mileage was the main reason.

Only after the immediate improvement did I recall those conversations with those various "pros" about mileage. Then I made this report for anyone who wondered about the o2 replacement effects.

Mileage sucked but wasn't going to replace sensors until 100k... why the hell would anyone do that before the recommended period? You think I'm a monkey? Oooh wait.. you do.
But hey... project away.
 

The Convert

Captain
Jun 4, 2017
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Yeah... I replaced almost every replaceable part... because they were all due. The fact that I saw no mileage improvement does not mean that gas mileage was the main reason.

Only after the immediate improvement did I recall those conversations with those various "pros" about mileage. Then I made this report for anyone who wondered about the o2 replacement effects.

Mileage sucked but wasn't going to replace sensors until 100k... why the hell would anyone do that before the recommended period? You think I'm a monkey? Oooh wait.. you do.
But hey... project away.
1. Anecdotal means that it is lacking data. Your personal account, with no logs, makes your conclusion textbook anecdotal. It doesn't mean you're wrong. It just means you can't prove it definitively or say how much of the percentage of improvement is based solely on the O2 replacement.

2. Parts fail early all the time. The time or mileage intervals are averages, not absolutes...especially if your car is not bone stock.
 

langsbr

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LOL - I quit replying because you became a baby and started cussing. You still fail to acknowledge that logs would have provided any insight to the issue. Perhaps your method of troubleshooting is replace something, test, replace next, test, repeat until you finally get it right, then claim victory. That's not how it's done. But keep swapping parts...
 
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matreyia

Major
Apr 19, 2017
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1. Anecdotal means that it is lacking data. Your personal account, with no logs, makes your conclusion textbook anecdotal. It doesn't mean you're wrong. It just means you can't prove it definitively or say how much of the percentage of improvement is based solely on the O2 replacement.

2. Parts fail early all the time. The time or mileage intervals are averages, not absolutes...especially if your car is not bone stock.
By data you mean measurements from the computer? Exact rates etc...

So my analog eyeball seeing 3xx miles as opposed to 160 mile on a tank means nothing... again, ignore the post. It is useless you anyone who wants computer data.