bad o2 sensor = ??

[Bwana]

What does a bad o2 sensor do to performance, specifically HP and gas mileage?

[SVXelerator]

There's a good chance your air-fuel mixture will be "off" - more than likely too rich or too lean. If you see a significant change in your gas mileage the O2 sensor is a good place to start looking.
(better yet-- a bad one should throw a code...)

So what kind of code ? My check engine light sometimes would not go on when cold start, but will stay there after the first start-up. I am suspecting it is from O2 sensors....

[lee]

Originally posted by Bwana
What does a bad o2 sensor do to performance, specifically HP and gas mileage?

stolen from somewhere on the web....

Typically, a bad O2 sensor will read low (lean), which causes the engine to run too rich, pollute too much and use too much gas. A low reading can be caused by several things: old age, contamination, a bad wiring connection, or an ignition or compression problem in the engine.

As an O2 sensor ages, it doesn’t react as quickly as it once did. The increased lag time makes the sensor sluggish and prevents the engine from keeping the air/fuel mixture in close balance. If the engine burns oil or develops an internal coolant leak, the sensor element may become contaminated causing the sensor to fail.

Because the sensor reacts to oxygen in the exhaust and not fuel, any engine problem that allows unburned air to pass through the cylinders will also trick an O2 sensor into reading lean. A misfiring spark plug or a leaky exhaust valve - even a leak in the exhaust manifold gasket - may allow enough air into the exhaust to screw up the sensor readings. It won’t damage the sensor, but it will create a rich running condition that hurts emissions and fuel economy.

[n00b on demand]

I wonder if my hesitation problems could be because of a bad o2 sensor...the hesitation has gotten much better with the K&N filter for some reason. My CE light did flash twice in the summer for 1 second.

[Bwana]

Cool, thanks guys. I had the code read, and it said O2 sensor, that's why i was asking...so i KNOW it's the o2 sensor.

Just wondering what actually happens when it's bad.

Now that I think about it, my gas mileage probably is worse. I'm getting about the same miles per tank in my 96 as i was in my 94...but on the 96 all of my miles are highway.

Thanks again.

[Chiketkd]

Originally posted by Bwana
Cool, thanks guys. I had the code read, and it said O2 sensor, that's why i was asking...so i KNOW it's the o2 sensor.

Just wondering what actually happens when it's bad.

Now that I think about it, my gas mileage probably is worse. I'm getting about the same miles per tank in my 96 as i was in my 94...but on the 96 all of my miles are highway.

Thanks again.

Bwana,

You have a '96 SVX with an OBDII system like myself.

This code you got for the O2 sensor, is it for one of the front two sensors, or for the third sensor? The front two sensors actively communicate with the ECU to adjust the afr to optimum.

The third sensor can be deleted with out having any affect on performance. Several WRX/STI guys have done this with an O2 simulator from Perrin (allows the entire cat to be removed and a straight-pipe installed).

-Chike

[Beav]

Originally posted by Chiketkd

... with an O2 simulator from Perrin (allows the entire cat to be removed and a straight-pipe installed).

-Chike

Otherwise known as a half-dead AA battery?

[SilverSpear]

there is something I cannot understand... I don't have O2 sensors in my car, my gas mileage is very good (16mpg), how come?

[Bwana]

Originally posted by Chiketkd

Bwana,

You have a '96 SVX with an OBDII system like myself.

This code you got for the O2 sensor, is it for one of the front two sensors, or for the third sensor? The front two sensors actively communicate with the ECU to adjust the afr to optimum.

The third sensor can be deleted with out having any affect on performance. Several WRX/STI guys have done this with an O2 simulator from Perrin (allows the entire cat to be removed and a straight-pipe installed).

-Chike

I'm at school right now, and the paper work and stuff is at home...but if I had to take a guess at which one it said...it would be....
i thought it said something to the effect of bank 3 row 1...or row 3 bank 1? i have no idea, ill look tomorrow when i go home.

[Chiketkd]

Originally posted by Bwana
I'm at school right now, and the paper work and stuff is at home...but if I had to take a guess at which one it said...it would be....
i thought it said something to the effect of bank 3 row 1...or row 3 bank 1? i have no idea, ill look tomorrow when i go home.

Definitely check. I'd also be interested in knowing which exact code you got.

-Chike

During lecture today we had a discussion on how pre-OBDII cars ('95 and below) can set an O2 Sensor code because of a failing MAF.

Originally posted by SilverSpear
there is something I cannot understand... I don't have O2 sensors in my car, my gas mileage is very good (16mpg), how come?

Are you joking? 16 mpg is not good. Does your car have Catylitic converters or any emissions equipment for that matter? O2 sensors are an intregal part of Fuel delivery and metering; for your car to simply not have them is very perplexing.

[Chiketkd]

Originally posted by SEA Sleeper
During lecture today we had a discussion on how pre-OBDII cars ('95 and below) can set an O2 Sensor code because of a failing MAF.

Are you joking? 16 mpg is not good.

Or from a failing fuel pump which could also cause a lean condition...

-Chike

P.S. I have to agree, 16 mpg is not good even if you're doing all city driving. Should be at least 3-4 mpg better.

[Beav]

Those are both reasons why trotting down to the local parts store and buying parts based on the codes pulled are NOT a good idea or in one's best financial interest. Codes are just a starting point in diagnosing a problem.

[Bwana]

Ok, it was code:
P0145 - O2 Sensor Circuit Slow Response (Bank 1 Sensor 3)