O2 sensor gone bad?

I'm getting bad MPG on my car and I'm wondering about the O2 sensor. All my maintence is up to date, my engine runs smooth, and my exaust is clean so I'm not sure where the problem lies. How much could a broken O2 sensor affect the MPG? Also if it is busted how would I know?

the first question is, why do you say you are getting bad mileage? what are you getting now, and what have you been getting in the past? what kind of car do you drive (model, trim, year)?

a bad O2 sensor will either make your car run rich or lean. the easiest way to check which it is, is to look at your plugs. if they are black, you are running rich. if they are more of a light gray color, you are running lean. you want a brown color i believe. i could have the lean and stoich colors backwards. what color are your plugs?

you say your maintenance is up to date, what do you mean by that? what have you had done, and how long ago was it?

Ok well I bought the 94 del Sol VTEC about 6 months ago. When I got the car it got around 15 MPG. If I remember correctly I should be getting around 28 (I do a mix of highway and city). I replaced the air filter, fuel filter, spark plugs, spark splug wires, distributer cap, and rotor all with top quality parts. Now I get like 18 MPG. All of this was done about 3-4 months ago. Would these relatively new plugs even have color on them yet? I've only put about 3K miles since the maintenance. Also I don't do any high revving on the engine.

if it is a bad O2 Sensor, the engine light should come on, if it is bad it can cost you surprisingly upto $150, in my case it did, try and go to a salvage yard or something.

any car that gets about half the mileage it should, usually has more serious problems that just needing a tune up. i would make sure its getting good compression, so that each detonation isnt wasting half of its energy. also make sure that your valves are lashed and injectors are clean. check your ignition system to make sure its firing every time also, and not just wasting good fuel by not igniting it.

My engine runs beuatifuly though so I highly doubt that's where the problem lies. If there was a compression, valve, or injector problem I think I'd be able to feel it in acceleration. Actually I'd say the engine is the part of the car that's in the best condition. Same goes for the ignition, if there was any misfiring or anything I would be able to feel it. Since I changed the ignition parts recently I have looked at it though and everything seems perfect. So you can see why I'm unsure of where the problem lies. If the engine and ignition runs great then the only other thing I would think could affect the milage would be something in the exhaust. For most exhaust problems the smoke would be discolored blue or black I'd assume but the smoke is clean. My last guess is the O2 sensor. Any idea if a bad sensor would affect the color of the smoke? Also I see you have a del sol VTEC too, just out of curiosity what kind of milage do you get?

in my car i get anywhere from 28-31, depending on the time of year and how i drive.

if your engine is running perfectly fine, but only measures half as efficient as it should, than i would assume that its your way of calculating mileage. a car that gets half the mileage it should, should be running poorly, leading to clues as to where the gas is getting wasted.

i still dont understand why you are placing the blame on the exhaust system, though. if it was exhaust, it would be the cat or a whole in the system somewhere, both of which would affect the performance of the car. a bad O2 sensor would also affect the performance of your car, as well as throw a code.

Well I definatly do the math right. I just got gas and did the calculations and I got 20.4, much better than usual. It just doesn't make any sense how a smooth accelerating engine could be doing this. Plus I don't even get an engine light saying the ECU finds anything wrong. I was just wondering about the exhaust because it's an aftermarket RS*R catback the previous owner installed so I was thinking maybe they did something wrong but I guess if they did I'd feel it when I drove. I'll probably end up having to take it to Honda. Thanks for your help, I appreciate it.

i just changed my o2 sensor up front and my check engine light comes on now. any ideas how to get rid of it? or how to get the codes to see what is wrong? thanks!

First of all, with a new ANYTHING, reset the ECU. 1.Take off the negative cable, 2. Remove underhood ECU fuse (15), 3. and the backup fuse (7.5). All for 15 Finutes, if that dont work. Go to http://www.automotiveforums.com/vbulletin/t19102.html
and
http://www.automotiveforums.com/vbulletin/t15933.html
for more info.

Good luck, oh and make sure all the O2 sensor wires are connected and free from rust and stuff.

You really dont have a big prob :)

thanks for the info. i'll try that later becuz after the check engine light came on, i decided to put back the original o2 sensor, and the light went away. just wanted to know if that was a bad move? i'll retry the new sensor when i get a chance.

By any chance was the newer O2 Sensor made by Bosch??? Many Hondas are not really compatible with different types of Bosch Products.

actually it was a bosch sensor. i tried clearing the code when it was on and it went off for a minute and it came back on again. thats when i switched it back to the old one. maybe i should take it back to pep boys?

yes try and take it back, dont put your old one back on. look around the internet and other stores to buy one that is not Bosch, Honda sometimes reject Bosch for some reason....

i actually did put back the old sensor on, is this a big problem? and i don't know if i can take back the new one to pep boys so i'll need some way to make it work if possible. btw, the code i pulled was a 02 sensor heater #41

i have always wanderd what that code was, i have no idea what the O2 sensor heater is.

are you sure about the Bosch not being compatible? it says its a universal fit. i don't wanna get stuck with it.

it says universal fit, it will fit, but it just may not work, if you buy it, make sure it is returnable....Bosch, alot of the time, is not technically compatable, it has something to do with electronics. very complicated....

well i reinstalled the bosch sensor and crossed my fingers. i reset the ecu and started the car. the check engine light came on again and idle was around 3000. drove for a while, reset ecu again and the check engine light came on again and the car is still idling low..i guess i'll try another sensor

try ebay.com
i was looking for a o2 sensor for my 93 EX, i ran upon many six generation honda sensors, very cheap..look for where it says "genuine, honda, oem" words.

In order for the O2 sensor to work properly, it has to stay in the 600 degree range. Otherwise, the ECU will think it's got bad sensor from it cooling down, so thats one of the reasons the heater is for. Some have been known to last the life time of a car. However with the crap they call gas now, it may be shorting the life of them...

"Noth'in like Induction..." ;)

Originally posted by m3kidds
well i reinstalled the bosch sensor and crossed my fingers. i reset the ecu and started the car. the check engine light came on again and idle was around 3000. drove for a while, reset ecu again and the check engine light came on again and the car is still idling low..i guess i'll try another sensor


dude if youre idling at 3000, there is definitely something wrong. check to see if the new o2 sensor is heated. i believe that your car comes with a heated sensor, so if the bosch one is not heated then that is most likely your problem. in any case, put back in your original until you figure out if the bosch is heated because its definitley not doing good for your car.

Okay well I'm new here and new to the honda I bought but just a tip for you guys. My CEL light came on and i had autozone do a codecheck and it came up being a o2 sensor pre cat right at the exhaust manifold. The car i bought was a 96 civic ex with 90k miles on it. Noone had the part so I called honda. The guy asked for my vin number and he told me the o2 sensor has a 150k mile warranty. They are replacing it for free and even offered to change my oil. I already did that so they are giving the stuff to me. Might want to give it a try..

my bad guys, i meant my idle was at 300 not 3K.. anyways.. the car was idling near stalling.. but i changed the o2 sensor back to the old original one, reset ecu and everything worked fine again. i guess you guys were right on the bosch not being compatible. as for the 150k warranty i'll have to call up to see if that could work for me. i have 108k on my 97. i even spoke to a guy at autozone and he said that the bosch should have worked. who knows.. any ways i'll call honda and see what they say.