Bad o2 sensor??

[bballr4567]

Ok so just recently I took a highway trip and got about 27-28 MPG going about 75 the whole way. Came back to campbell and filled her up and now after driving about 150 miles I need to fill her up again. Ive got no loss of power, no hesitation at any speed and no weird smells at all. I just recently did the battery cable service because I had to get a new battery so I did it at the same time, made sense to me.

Yes I know the gauge could be wrong but I highly doubt that because every time I fill it up and its near empty I can get close to 13 gallons in it. I just recently ran a bottle of Lucas fuel treatment in it so I dont think 3 tanks later it needs it again.

Now all this has me thinking that the front o2 sensor is going bad. Any opinions out there??

[Brandon]

my grand am only gets about 210 miles to the tank... way less if im stomping on it... on the interstate shell do a lot better..... almost sounds normal to me.

[bballr4567]

I used to get about 270-300 to a tank driving mixed highway and city. Now its probably about 200 and thats a huge difference.

[00SilverGA]

Originally posted by bballr4567
I used to get about 270-300 to a tank driving mixed highway and city. Now its probably about 200 and thats a huge difference.

Really?? :???: I don't even get close to that with my 2.4L. About 90% of my driving is highway too. Most of the time I get about 200 a tank. Does anyone have any suggestions on why this is. I don't really have a lead foot either.

[rixGAphx]

Originally posted by 00SilverGA
I don't even get close to that with my 2.4L.
Most of the time I get about 200 a tank.
Does anyone have any suggestions on why this is? Because we don't know how many gallons YOU use in 'a tank'.

Some people put in 4, others put in 14.

Translate your 'miles per tank' into the more-conventional and useful 'miles per gallon' that we can use as a reference.
* * *
Bballr, your 27-28 mpg at 75 was about right.
How many miles on your '01, about 70k for a 6-yr old?

The O2 sensor will last 100k miles, but it will become increasingly inaccurate for the last 40k of that.
The PCM doesn't consider this deterioration to be failure, so it won't set a code.
And the inaccuracy is generally reflected by increasingly poorer gas milage.
You can remove the sensor and have AutoZone/Checker/etc. do a benchtop test, should be a free test.

Let us know how many gallons you used for the last 150 miles;
yes, the gage CAN be that far-off.
Especially if the gage sender has recently 'taken a powder', as opposed to the O2 sensor suddenly becoming very inaccurate.

Finally, check the air filter.
A crap-load of dust or ingested butterflies or whatever could heavily block it, with poor milage as the main indice.

Hope this helps,
-Rick

PS: Replacing plugs and wires at about 60k is also beneficial for fuel milage, + a little more action from the stoopid pedal :D

[bballr4567]

Ok the car has 143k on it.

New plugs & wires and intake at 132k. Fuel filter was put on at 140k. No SES codes so that is why I was thinking bad sensor. Ill fill the car up soon and let ya know how many gallons it took.


Yes I know thats a ton of miles but almost 80k were put on the car in the first two years of its life.

[04alyGT]

Well my o2 sensor went out last summer and i was getting god aweful gas mileage, about the same as you are reporting. Along with that i was getting a black sooty build-up on the pipes and the back of the car, do you have that? Also when mine was out i noticed that when i was cruising especially around 60 it would run very rough like it was injecting too much fuel.
Hope that helps

[rixGAphx]

Originally posted by bballr4567
Ok the car has 143k on it. If that's the original sensor, OF COURSE it's failing.
It has a couple metal leaves that are coated with precious metals, platinum and rhodium I think, and the metals eventually burn-off.
So the chemical reactions don't occur as rapidly as they should, and the PCM doesn't properly adjust the fuel trim.

Replace it, about $50 + the special $10 universal O2 socket.
On the V6, it's kinda difficult to access with any other kind of wrench.

[bballr4567]

Nah not getting a rough condition at all. In fact it runs smooth all the way up to 85 but havent taken it higher then that. No soot either.

[bballr4567]

Yea thats what I was figuring Rick. Not sure if its the original but its the only thing that I can think of that would cause this kind of MPG loss.

Now what o2 sensor should I get?? Will the regular OEM sensor work or should I get a different one for my soon to be FI setup??

[rixGAphx]

Originally posted by bballr4567
Will the regular OEM sensor work or should I get a different one for my soon to be FI setup?? Huh?

You're gonna race Formula One with teh GA????

[bballr4567]

A capital i is I and a one is 1. lol


<------- Look at avatar.

[4kQuad]

In the Camry I get 30 ~ 32 on the freeway, I get 24~26 around town. So I get say about 5 miles less per gallon, times that by 15 and get 75 miles per tank differance. My Ga 2.3 Quad got over 400 out of one tank freeway driving, while I normally only got 220 to 260 per tank.

I bet another freeway rip would bring the miles right back up.
:penny:

[bballr4567]

Why would another road trip bring the miles back up??? Ohhh forgot to mention but I used to get about 31-32 MPG on the highway. So there is a drop there also.

Also the temp the past few weeks here it hasnt been under 50 much. Its usually right at it in the morning and up in the high 60s low 70s for the high so its not winter making me get worse MPG.

[4kQuad]

Road trip wouldn't bring them back up so to speak. But if freeway milage has also dropped...then never mind.

I thought maybe you were comparing the milage and city driving just don't compare to freeway as far as mpg.

Could be the 02, how old are the plugs, could be there not working as well now. If all around milage is down. Air fliter and tire pressure should also be considered.

[SE2000]

Ignoring the trip mileage, what was your average mileage between fillups?
Maybe you got a heavy tank of winter gas and you're driving in warm weather.
If you problem persists, do you have access to a smog test machine, that would give you an idea of fuel problems such as the sensor.

[bballr4567]

My average tank was usually 270-300.

Im not sure about the smog test machine seeing how they dont test for that in either KY or TN. Wouldnt have any idea where to find one at.


Also I already noted that plugs were changed about 10k miles ago and a new air filter was put in at the same time.

[04alyGT]

Well i may be wrong but i remember seeing in a post about how occasionally you can fill up with a bad tank of gas which will kill your mileage while your running that tank of fuel.
Also IIRC the black build-up on my pipes didn't happen right away, it may have taken a week or something before i noticed it.

[bballr4567]

I just dont think its that due to the fact that the MPG has been going down steadily with the exception of getting the new fuel filter on which made it go up slighty.

I ALWAYS due the MPG after every single fill up. Its something I have done since I started driving since I was 15. Lets you know if something is going on with the car.

[SE2000]

I don't know if there are still test facilities, I guess the state eliminated the requirement. I did find a pdf about it

http://www.air.ky.gov/NR/rdonlyres/35A8600F-D8DB-4F6A-935F-F51907A19379/0/EmissionsFactSheet.pdf

[bballr4567]

Yea thats about a 5 hour drive to get up to those counties. I called the DMV here and they didnt even know what an emissions test was and that was after talking to three people.

[echoicse]

Josh, I would do what Rick told you first...clean/replace your air filter to your cold intake system. If you want to check it quickly-take the filter off and look thru it into bright light-if you can't see light thru it,you'll know what to do. Also, I would see if the throttle body needs a cleaning with carb. cleaner inside. And, when was the last time you changed your PCV (positive crankcase vent.)? Lastly, since your a Soldier and buy your fuel at the Shopette...talking to my Son, Soldier also (who owns a SVT 'Stang), your lowest fuel is 87 octane, so you might want to upgrade to a 93 higher octane-detonation thing!

[bballr4567]

The filter is clean as can be. Its a K&N and is a little dirty but still pretty dang clean.

Hmmm good point about the TB. Never thought about that. Ill try it out.

Never thought about the PCV either. I know that if its cracked it will provide for some bad MPG correct?


The gas thing has already proven to be bunk for me. I tried 91 for a while and it did nothing to benefit the car. Just was wasting my money so I went back to 87.

[echoicse]

Originally posted by bballr4567
The filter is clean as can be. Its a K&N and is a little dirty but still pretty dang clean.

Hmmm good point about the TB. Never thought about that. Ill try it out.

Never thought about the PCV either. I know that if its cracked it will provide for some bad MPG correct?


The gas thing has already proven to be bunk for me. I tried 91 for a while and it did nothing to benefit the car. Just was wasting my money so I went back to 87.

Josh, regarding PCV-Yes... the PCV after the aging process can become stuck also. Understand about the octane,also!

[bballr4567]

Hmmm all right. Got an idea of where I can locate it on the car?? Well its part of the emissions correct?? So then there should be a map of it under my hood right?

[echoicse]

Josh, I believe your 3.4 engine still has one like the 3.1. The location is front rocker (valve) cover to the right side. PCV should be almost be at the end of the rocker (valve) cover.

[echoicse]

^^^ Josh, another idea-and how's your GrandAm running? Check the rubber hoses that lead to any sensors,etc. I know the rubber hose that leads to the MAP sensor becomes hard and brittle over time,esp. where the hose meets the map sensor nipple. I check these hoses periodicity to see if their no good and replace them-they need to be soft.

[bballr4567]

Well Im about to step out and go get an o2 sensor. Called a mechinac here and he said that more then likely it is the sensor due to the gradual decline in MPG.

Im going to get some throttle body cleaner too though. Pulled the intake off and it looks pretty nasty in there.

[echoicse]

Originally posted by bballr4567
Well Im about to step out and go get an o2 sensor. Called a mechinac here and he said that more then likely it is the sensor due to the gradual decline in MPG.

Im going to get some throttle body cleaner too though. Pulled the intake off and it looks pretty nasty in there.

Thanks for the info.!!!I was wondering how it was going! Keep us,me, informed if you can. Thanks! Echo.

[bballr4567]

So just got done with changing the sensor. Tried to do it with the coil packs in place but yea gave up on that rather fast. Moved them out of the way and went smooth smooth. The old O2 sensor looks a little charred but I dunno.

Cleaned out the TB also and my god. lol It was pretty damn dirty. Tons of built up gunk but now its nice and shiny.

Car responds a little better now and the exhaust doesnt smell like it did before so Im guessing the new sensor is doing its job.

BTW those damn sensors are expensive. lol

[echoicse]

^^^ I found out a-time-ago the fuels and additives that they put in seems to gunk up the throttle bodies more. How much did the 02 sensor cost you...betting over $65.00? Hey, and buying off base,of course, did they give you military discount? When I was a volunteer firefighter AutoZone would give me a % off the cost w/ ID.

[bballr4567]

Ohhh forgot to add that I got 15.7 MPG on that last tank of gas. Sorry that is just plain wrong for highway and city driving.


The sensor was right at a 100 because its the upstream one and it was the exact one. I wasnt about the universal at all. Screw that. Autozone here gives us a 11.5% discount so its not all that bad I guess.

[echoicse]

WWWOOWW,$100 for a 02 sensor, I guess I was off $35.00! Pricey parts! Discounts, no matter what they are-are-a-good-thing. Check your MAP sensor, etc. hoses to see if their bad? If you have time I'd pull the spark plugs, with the tbi dirty and now cleaned, your plugs might be fowled.

[bballr4567]

Yea I checked all those hoses and everything was in good shape. I doubt the plugs are fouled now because the TB cleaner I got said to turn off the car and spray and let it set for 60 seconds then wipe it clean.

I might pull the front three just in case.

And yes they are pretty expensive, the fronts are more then the back. They had a universal one where you just cut and splice the old wires and plug it in but after my last wiring episode I paid the extra $25. lol

[echoicse]

Yea, your right on with the splice-and-dice routine with the 02 universal sensor. My Son and I, before he got his SVT, has a V6 'stang that we put headers on. Because of this we had to extend the 02 sensors with splice-and-dice. Man, what a freak'in project!! Should've/Could've time-bought extension 02 asy. for this type of project!

[bballr4567]

Well finally went through a tank of gas and filler her up. 12.4 Gallons and 252 miles and that was a MPG of 20.2 with the same driving and almost exactly same mix of highway and city. Now tell me thats not a huge step up from 15.7!!!!!

Thanks for the help again guys.

[Coondog]

Could be a clogged/stuck EGR valve. That'll cause shitty mileage. Especially in the city.

[bballr4567]

EGR is brand new and has about 6k miles on it. Trust me this fixed it for sure.

[rixGAphx]

Glad you are again purring along with acceptable milage! :D :-Rick

[bballr4567]

Believe me so am I. I love to drive so the low MPG killed me. Ive had the car for about 6 months and Ive put almost 13k miles on it. lol

[bballr4567]

Another update on this as I finally got to take a highway trip. Got 362.1 miles on 13.002 gallons for a MPG of 27.8. Mind you I was going about 80 and in very mountainous areas too.


Needless to say I think the O2 sensor was bad!!!!

[FasTBird232]

I'm just gonna hop in on this thread...

Ok, O2 sensor went bad last fall. Changed it. Things were fine up until a few weeks ago. SES light flicks on just as I notice my gas mileage going to hell again. Sure enough, that same sensor is dead again (scan tool confirmed). Now, this motor eats oil like you're pouring it on the ground. I'm assuming the burning oil is fouling the sensor. So, how do I go about fixing this headache? My city mileage is nothing less than atrocious, so I can't just ignore this.

[tenspeed]

Originally posted by FasTBird232
Now, this motor eats oil like you're pouring it on the ground. I'm assuming the burning oil is fouling the sensor. So, how do I go about fixing this headache?

The expensive way is to rebuild the engine.

I went the cheap route with my 2.4L and used 20w50 in the summer and 10W40 in the winter. It reduced the oil consumption to a quart every 1500 miles. I would check and top off every 1000 miles and change every 5000.

[SilverCoupe]

hi people.. i recently bought my car and i tested the gas mileage,, im also sadly getting about 15MPG mixed city\highway and its pissing me off.. especially because my dad's minivan with the same engine (venture) is getting more..
i have no SES light on. but i was wondering if theres a way to check it,, one person said i can take it to auto zone and they'll check it,, but do i need to take it out? and if i do,, how do i take t out? can someone post a step by step with pictures?
thanks in advance!