I have a 92 grand prix with a 3.1 146,000 miles...runs great except it gets crappy mileage maybe 280-300 a tank full through town..a tad better on highway...I have replaced the plugs wires,fuel filter,air filter, whats next?..Oxygen sensor? but it doesnt throw that code?

How many gallons do you use in that amount of mileage? I'm assuming the GPs have used the same size fuel tank over the years. I run my car until the light comes on and usually get to about 310 miles on the tank. That usually equates to about 13.5 gal.

That is mixed hwy and city driving.

It's hard to complain about fuel mileage this time of the year since the gas isn't as good, the car takes longer to warm up, you're using the A/C for defrost a lot and overall it's just a time of the year where fuel mileage usually goes down about 2-3mpg.

When was the O2 sensor changed last? If you haven't changed it in a while it could account for your mileage issues. Even though you don't have a light that doesn't mean that the sensor is not getting old and not monitoring at optimal levels. These sensors go out gradually and fuel mileage decrease in a good indicator. Change it and see what happens. Just don't use Bosch sensors they are junk and you will change it again in short order. Stick with and OEM sensor.

When was the O2 sensor changed last? If you haven't changed it in a while it could account for your mileage issues. Even though you don't have a light that doesn't mean that the sensor is not getting old and not monitoring at optimal levels. These sensors go out gradually and fuel mileage decrease in a good indicator. Change it and see what happens. Just don't use Bosch sensors they are junk and you will change it again in short order. Stick with and OEM sensor.


Hi I dont know when it was last done I bought this car with 138000 miles and it seems like the mileage has been steadily getting worse?.Been driving my gf's 94 grnd am damn thing gets 400 miles to a tank and its smaller ...I hope i never fix her window,lol....Part number for the sensor? can i change it myslef or they a bit**??
thanks!!

Again, the amount of miles you get per tank means NOTHING. It's all about miles per gallon. Your 92 GP might have a smaller fuel tank than the 94 GAM. Just take the total number of miles driven divided by the amount of gallons until the car is full and there's your MPG.

As far as the O2 sensor, rockauto.com is a good place to go to at least to find the part number since they have a really good database of parts for your vehicle.

I believe since your car is pre-OBDII you'll just have one O2 sensor and it should be right in the exhaust manifold on the backside of the engine. It does take a special tool to remove unless you can shoe-horn a Crescent wrench in there and get good enough of a grip on it. A standard socket won't work because of the wire harness coming out the top of the sensor.

Again, the amount of miles you get per tank means NOTHING. It's all about miles per gallon. Your 92 GP might have a smaller fuel tank than the 94 GAM. Just take the total number of miles driven divided by the amount of gallons until the car is full and there's your MPG.

As far as the O2 sensor, rockauto.com is a good place to go to at least to find the part number since they have a really good database of parts for your vehicle.

I believe since your car is pre-OBDII you'll just have one O2 sensor and it should be right in the exhaust manifold on the backside of the engine. It does take a special tool to remove unless you can shoe-horn a Crescent wrench in there and get good enough of a grip on it. A standard socket won't work because of the wire harness coming out the top of the sensor.


thanks !! Actually her car has alot smaller tank than mine mine will take 30 plus to fill it and her will be full around 25 or so...I am guesing my tank is around 15-16 gallons..thanks for the link also

AC Delco 215503 front sensor, in the Y pipe area AFS21 you can find both at Rockauto.com for a very reasonable price. Also you can change them yourself but you will need an O2 sensor socket about $10 at an autoparts store.

AC Delco 215503 front sensor, in the Y pipe area AFS21 you can find both at Rockauto.com for a very reasonable price. Also you can change them yourself but you will need an O2 sensor socket about $10 at an autoparts store.

thanks mine is in the back is that the y pipe AFS21 one?also cant you get a wrench back there or no?or just use a regular socket..as i am putting on a new one on anyway..so i will just cut the wire?

thanks guys!!!

thanks mine is in the back is that the y pipe AFS21 one?also cant you get a wrench back there or no?or just use a regular socket..as i am putting on a new one on anyway..so i will just cut the wire?

thanks guys!!!
which one of these also will work?
http://www.partsamerica.com/ProductList.aspx?parttype=291&ptset=A&searchfor=Oxygen+Sensor

Go with the standard motor products one. They make a good product that is reliable.

That link doesn't work but I punched in your car data on that site and they show BorgWarner and Bosch sensors and it looks like all they have is upstream sensors. Evidently your car has dual sensors.

I'd just go with the AC Delco sensors from rockauto.com because they have both of them and AC is the prefered sensor. I have Bosch sensors on my 97 GP and don't have any problems but I replaced them only six months ago so time will tell...

That link doesn't work but I punched in your car data on that site and they show BorgWarner and Bosch sensors and it looks like all they have is upstream sensors. Evidently your car has dual sensors.

I'd just go with the AC Delco sensors from rockauto.com because they have both of them and AC is the prefered sensor. I have Bosch sensors on my 97 GP and don't have any problems but I replaced them only six months ago so time will tell...


from what i can tell it just has the one in back?...where would the other be?

Just follow the exhaust from the front downstream and you should see two sensors. The Y-Pipe is the area where the two exhaust streams connect.

Just follow the exhaust from the front downstream and you should see two sensors. The Y-Pipe is the area where the two exhaust streams connect.


Do I have to replace both then if it has 2?

Yes, if you have two then replace both of them. This will eliminate problems later on and the engine should operate more efficiently.

Actually, the sensor just ahead of the converter (if so equipped) isn't an O2 sensor, it's called a catalytic converter temp warning sensor. You only have one O2 sensor, and it's in the rear manifold. DO NOT buy a Bosch sensor, they are JUNK!!!!!! If you can't find a Delco in your area, buy the Standard Ignition brand one, as they are good quality. Also, to remove the old sensor, cut the wires off and use a spark plug or deep well socket, then use a wrench to install the new one.

A-HA! I thought for sure his car would only have one 02 sensor since it's OBDI. That explains it all Rich.

Actually, the sensor just ahead of the converter (if so equipped) isn't an O2 sensor, it's called a catalytic converter temp warning sensor. You only have one O2 sensor, and it's in the rear manifold. DO NOT buy a Bosch sensor, they are JUNK!!!!!! If you can't find a Delco in your area, buy the Standard Ignition brand one, as they are good quality. Also, to remove the old sensor, cut the wires off and use a spark plug or deep well socket, then use a wrench to install the new one.

thanks!! How do you get back there to do that? from the top or underneath?

Put your knees up on the intake manifold and look down on the backside of the engine. You should see the pipe from the front exhaust manifold join with the rear manifold and then just beyond that is the O2 sensor.

Thanks I seen it back there...,but whats the best way to change them top ?bottom?