02 sensor, How hard to replace?

I drive a '95 caprice w/ 125,000 and get horrible gas milage. I've been reading in the forums and I think I might need a new 02 sensor. I've changed the plugs, fuel filter, and it still only gets 10mpg around town. How do I know when to change the 02 sensor and how hard is it to replace? I can do basics like change my oil, transmission fluid, brakes front and back, and my spark plugs, so can I change the 02 myself?

I drive a '95 caprice w/ 125,000 and get horrible gas milage. I've been reading in the forums and I think I might need a new 02 sensor. I've changed the plugs, fuel filter, and it still only gets 10mpg around town. How do I know when to change the 02 sensor and how hard is it to replace? I can do basics like change my oil, transmission fluid, brakes front and back, and my spark plugs, so can I change the 02 myself?

What engine do you have?

What rear axle ratio do you have?

The EGO sensor is no harder to replace than a spark plug - but don't change it without checking other things too. Do you get the service engine soon light on the dash?

I have the L99, I'm not sure on the rear axle ratio, where can I find that info?
oh and the service engine light isn't on.....

edit: BTW my temp. gauge isn't working properly, it stays on the left and only sometimes it reads the correct temp. Would that have anything to do with the mpg I'm getting?

I have the L99, I'm not sure on the rear axle ratio, where can I find that info?
oh and the service engine light isn't on.....

The L99 is the 4.3 liter, correct? Okay, look on the "Service Parts Identification" label under the deck lid. Look for "Gxx", such as GU4, GX9 etc. My guess is that you have a GM8, which is a 2.56, but I could be wrong.

The smaller engine with the taller ratio around town could cause you to "stomp on it" more than the larger engine, resulting in poor economy.

Since you said the SES light was NOT on, if it smells rich then there is definitely the possibility of an EGO sensor failure. These are typically on the driver's exhaust manifold near the dump.

I just checked and it says "GU5"

I just checked and it says "GU5"

GU5 is 3.23 so that's decent, I would suppose to make up power from the smaller engine. It just might be a bad sensor causing the engine to run rich, and not setting the SES light.

Could the EGO sensor be the problem why mine runs rich?

I got a duty cycle meter and my M/c duty percent was 58%

Could the EGO sensor be the problem why mine runs rich?

I got a duty cycle meter and my M/c duty percent was 58%

It certainly could. It could be reporting a certain value that's off, causing the computer to compensate just enough that the MIL doesn't light.

are they real pricey, or can I get one for under 20$?

are they real pricey, or can I get one for under 20$?

$19 for a Bosch unit is what I paid for mine at Autozone about 3 years ago. I suspect they'd still be in that ballpark.

I just checked prices with autozone and napa and they were $55.99 each :banghead:
It says I need two, is that true? Does anyone know of any online sites that would be cheaper?
http://www.napaonline.com/images/u_clear.gif

Try www.RockAuto.com, they seem to have pretty good prices.

Do I need two oxygen sensors or just one????

Do I need two oxygen sensors or just one????

What would YOU think?

If one is bad, I'd do 'em both. To attempt to save some $$$ by only doing one is what we call "false economy". You spend less in the long run when you spend more to do it right the first time.

What would YOU think?

If one is bad, I'd do 'em both. To attempt to save some $$$ by only doing one is what we call "false economy". You spend less in the long run when you spend more to do it right the first time.

I've never replaced these sensors before on a car, I didn't know there was two, atleast now I know how many I need to get.

I've never replaced these sensors before on a car, I didn't know there was two, atleast now I know how many I need to get.

I know the L99 is single exhaust, and yours is a '95, which isn't OBDII. Perhaps Blue Bowtie can clarify this, but it might only have one on the driver side exhaust manifold. If it has two, the other one should be on the outlet side of the catalytic converter.

I know the L99 is single exhaust, and yours is a '95, which isn't OBDII. Perhaps Blue Bowtie can clarify this, but it might only have one on the driver side exhaust manifold. If it has two, the other one should be on the outlet side of the catalytic converter.

I'll check both of those spots this weekend when I get some time to get under the car, thanks.