A case for replacement of O2 sensor as prev. maint

[FusilliJerry82]

Since I've gotten this Protege in February, its gas mileage has been abnormally low for a 1.6L 4. Even the seller remarked so. However, it ran like a top and was in good condition, and even so was much less of a pig than my Explorer.

I've heard how an O2 sensor can kill gas mileage when out of whack, but I've never had a CEL, so I paid it no mind. The mediocrity of my mileage has gotten to me as of late however, so in a fit of frustration, I replaced the upstream O2 sensor with a universal Bosch. Since I've bought it, I've consistently gotten 19-21 MPG in mixed driving; besting at over 23 on a long trip. The first tank after replacement, I got just shy of 28 in mixed driving. At $70, if mileage holds anywhere near there, it will have paid for itself quick.

If you've got over 100k and have noticed your mileage has taken a dive, replacing the upstream (downstream is chiefly for monitoring the condition of the cat) O2 sensor(s) may be worth trying.

 

[beast3300]

I would suggest you get rid of your universal O2 and get a direct fit Denso. A couple other things to do are clean the MAF sensor with sensor safe spray. And remove and clean the EGR which are prone to deposits.

 

[Dave Hess]

Yep. Thats the # 1 mistake some people make..... using a universal Bosch O2 sensor. Rock Auto has Denso sensors, don't forget the 5% discount code.

Is it possible the injectors are dirty ?

 

[FusilliJerry82]

What's wrong with the Bosch? BTW, Rockauto's O2 sensors for this car are $10-20 more than Advance/Autozone surprisingly enough.

 

[The_Jeff]

I've used bosch universals, in fact the $18 one for many GMs. Cured my p0133, MPG is as good as it gets. Glad it worked for OP.

There may be finicky cars out there, but the physics of an o2 sensor don't have to be complicated unless the engineers make it so, eg with wierdly shaped exhaust manifolds needing special flutes or whatever.

 

[Dave Hess]

You should use the exact O2 sensor for your car, not a sensor that just happens to fit your car and 20 other cars.

When our old 1998 Civic needed an 02 sensor I bought a Denso when the original died. Before it died I notice the gas mileage dipped to 38 MPG. With the new sensor my wife's car easily got 42 MPG. Today my nephew has the car in TX and its still geting over 40 MPG with almost 260K miles.

I know many GM cars have good results with universal O2 sensors.

 

[FusilliJerry82]

Are the symptoms of a motor that doesn't like universal sensors usually immediate? If so, I'm lucky; it runs like a dream. All this aside, my main message still stands.

Also, I reread my first post and I should make a clarification. When I say "Since I bought it I've consistently...." I mean the car. So the mileage increased sharply after purchasing and installing the sensor.

Beast, is the 1.5L in your 98 the same as my 1.6L only smaller; the ZM? If so, have you had any instances of the EGR valve hurting fuel economy without any apparent idling or drivability issues?

 

[beast3300]

Originally Posted By: FusilliJerry82
Are the symptoms of a motor that doesn't like universal sensors usually immediate? If so, I'm lucky; it runs like a dream. All this aside, my main message still stands.

Beast, is the 1.5L in your 98 the same as my 1.6L only smaller; the ZM? If so, have you had any instances of the EGR valve hurting fuel economy without any apparent idling or drivability issues?

It's a Z5 engine. Whatever that means. I think the 1.6 is distributor-less so therefor alittle more sophisticated. EGR usually throws codes when it get's sticky but for preventative maintenance cleaning it is a good idea. Ever since the GF switched to the only top tier retailer 3 years ago the EGR hasn't thrown a code. But yes a EGR can decrease fuel economy without creating a large driveability issue.

Universal O2 sensors don't always show up in the form of a check engine light (obviously they can). Some of issues arise from universals having to do with resistance with butt connectors. Other issues have to do with heater circuit amp rating.

Her Protege gets 32 mpg consistently without cruise (female driver) around the speeds of 70mph. I don't ride with her to often but I can tell you she doesn't know how to coast. She only takes her foot off the gas to hit the brakes. I make her nervous is what she claims for that driving style. Anyway I digress......I'm sure it would get 35mpg or better with a better driver.

Goodluck,
Chuck

 

[Virtuoso]

I would like to know just how out-of-whack an O2 sensor has to be to trigger the CE light.

 

[beast3300]

Originally Posted By: Virtuoso
I would like to know just how out-of-whack an O2 sensor has to be to trigger the CE light.


Depends on the manufacture of the automobile. The PCMs are programmed differently. Some look at cross counts, some look at how high the sweep, how long does it stay in a specific region. The newer the car the more complicated everything is.

for example look at page 1 and 2 of this pdf. (open with internet explorer)
http://service.gm.com/gmspo/mode6/pdf/Bm...%203.6L_LY7.pdf

 

[Rabbler]

Depending on the sophistication of the cars OBD II system the O2 sensor can be extremely faulty and not trigger a code. Codes are triggered when the sensor performs outside normal parameters. As long as the sensor is reporting back a possible normal reading (which could be complete wrong based on how the engine is running)the MIL stays off.
If your O2 sensor has over 80K on it, its probably not responding fast enough and is a good candidate for replacement.

 

[SteveSRT8]

There is no magic number of miles to recommend replacement of O2 sensors.

 

[Trav]

+1 on a properly maintained engine that has no injector leakage,oil burning,contaminated with chemicals etc the O2 and cats can go a very long time and work perfectly well.

 

[rpn453]

I keep a spreadsheet with a graph of my fuel economy. If it starts trending up, changing the O2 sensor would be the first thing I do. I've got y=0.0008x+7.934 (liters/100km) for my linear trendline right now, so I'm still good!

 

[Vikas]

Don't you get different slope during winter vs summer?

 

[someguy]

I think Bosch recommends a 100K replacement interval. Was the old sensor dirty or gunked up at all?

 

[FusilliJerry82]

There was a grey carbon haze over it but it wasn't as bad as I expected.

 

[rpn453]

Originally Posted By: Vikas
Don't you get different slope during winter vs summer?


That's just a single trendline. I have no driving routines, so the data points are all over the place. I have averaged a little better mileage during the warmer months though. Summer mileage is 30.6 mpg while winter mileage is only 28.2 mpg. Spring is 30.2 and fall is 28.4.