O2 Sensor And Fuel Economy

[killerFatty]

I heard that if you have a bad O2 sensor you could be losing 40% of your fuel economy, and since Im getting about 8-10 w/ a little bit of a lead foot. I want to know if thats true. my car has 178K and has just been Tuned up and had all the fluids flushed. tires are filled up and oil is fresh, so the only thing i can think of is that O2 sensor. what do you guys think.

THX,

KILLERFATTY

[AZ Mike]

If your O2 sensor is bad, your car will throw a code and you know it needs to be replaced.

That being said, I have heard from some who seem to be "in the know" that O2 sensors do degrade over time before they actually fail. If this is true, it could impact fuel mixture and therefore mileage. I have heard that 100,000 miles is a reasonable interval for swapping O2 sensors if you do not want to wait until failure.

The above is "heresay" from reputable sources; in other words, I can not prove nor disprove it.

However, even if your O2 sensors were on the way out, I would speculate that they alone would not cause mileage to drop to 8-10 mpg, and that you may have other issues.

[killerFatty]

I have heard that 100,000 miles is a reasonable interval for swapping O2 sensors if you do not want to wait until failure.

thx i know that they have never been replaced and my car has 178k so I'll do those pretty soon. should i go oem or should universals work, and what things should i look for (If any) in good O2 sensors.

THX again

[Bali26]

check thermostat

[SKperformance]

All sensors wear over time, o2 sensors have a life of 200 000 before they should be replaced before the results are not accurate.

Change the temp sensor on the manifold , all 4 o2 sensors and clean you intake/MAF it should run much better . As the computer is now getting correct information to map .

Also if you have time buy a cheap grounding kit off of ebay and ground the engine and its supports. Unless you are good with tools and can make your own factory matched ones. If the ground are over 5 years old they will degrade and not provide a clear signal to the ecu as well.

[ono8ono]

Change the temp sensor on the manifold

Are you talking about the coolant temp sensor?

I'm thinking to change my 98 LS400 (78,000 miles) coolant temp sensor but I wonder what kind of mpg improvement I may get? I'm only getting 15mpg city.

Did you change yours? If so, any difference with mpg?

[killerFatty]

All sensors wear over time, o2 sensors have a life of 200 000 before they should be replaced before the results are not accurate.

Change the temp sensor on the manifold , all 4 o2 sensors and clean you intake/MAF it should run much better . As the computer is now getting correct information to map .

Also if you have time buy a cheap grounding kit off of ebay and ground the engine and its supports. Unless you are good with tools and can make your own factory matched ones. If the ground are over 5 years old they will degrade and not provide a clear signal to the ecu as well.

i can take care of th O2 sensors my self, but what is involved with the intake cleaning?

[AZ Mike]

Do a search on cleaning throttle body; I have seen a good DIY write-up on this in the past including photos.

[jcrome04]

how do you clean the MAF? sounds risky to me.

What is the procedure for the temp sensor on the manifold?

[c.word]

All sensors wear over time, o2 sensors have a life of 200 000 before they should be replaced before the results are not accurate.

Change the temp sensor on the manifold , all 4 o2 sensors and clean you intake/MAF it should run much better . As the computer is now getting correct information to map .

Also if you have time buy a cheap grounding kit off of ebay and ground the engine and its supports. Unless you are good with tools and can make your own factory matched ones. If the ground are over 5 years old they will degrade and not provide a clear signal to the ecu as well.

Good Oxygen Sensor Link:

http://www.bobblick.com/techref/projects/o...r/o2sensor.html

SK*!!! YES! Good point! One can spend hours and $$$ on parts, only to discover the sensor(s) may not be receiving correct current. With only a simple code reader, we could miss this data.

I do business (make friends) with local "service stations" (yes they still exist) who use some of these: http://www1.snapon.com/compareplatforms.nws

Code only is ok, but only if we *have* a trouble code. With a true scanner we can look deeply at all values of our engines' sensors. The fuel/air/exhaust/temperature relationships are truly fascinating. I would add -from experience- if OTHER issues result in changes to the normal exhaust composition, O2 sensors will foul & fail prematurely. Too much of anything (gas, oil, coolant) will slowly murder oxygen sensors over time.

If I may share my case... a defective intake gasket led to what was interpreted (by the oxygen sensor forward of the catalytic converter on the right bank) as a lean fuel/air mixture.

Result1 (without a check engine light): Computer calls for more fuel (fuel/air mixture) to all cylinders.

Result2: All oxygen sensors eventually foul from rich combustion effluent (incomplete burning of fuel/air mixture). Computer then turns on check engine light. When scanned, all O2 sensors show a rich fuel to air mixture. One oxygen sensor is flagged as bad by a code-only reader. I replaced it. (without knowing the cause of the rich fuel/air mixture stated previously)

Result3: another code on a different sensor. I replaced another, and another... NOT KNOWING WHY THEY WERE FAILING.

Six shops and two dealers looked at this, saw the codes, and replaced sensors.

Ultimately, my friends (see above) and I stopped and watched the values of the O sensors. They asked about the recent mechanical history. When I mentioned intake gasket, they did a smoke test which identified the bad intake gasket replaced two years before.

One and all had tunnel vision with the codes and not what was creating the codes. POINT: I and a lot of experienced mechanics became wrapped up in troubleshooting the symptom and not the problem.

One may say that I need to find better shops.

One may say that this is logic 101.

I am not wanting to debate, only share.

But the one thing I *DID* do is go back to everyone involved to share the solution...

and a chuckle.

[Alexander the o.k.]

Well written cword, and thanks for sharing that!

That sort of post is what makes the LOC an exceptional place. So few ever post back what the ultimate fix was, so it is especially appreciated!

SK, thank you as well for the excellent tips. When one has eliminated the notorious trunk hinge short, and other more mundane 'fixes', some mysterious electrical/ driveability problems may come down to a bad ground. If you have more info on how/where is best to ground, please let us know.

Your input here is highly valued.

Thanks again guys..

Kudos and