02 Sensor Questions

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3,082
Picked up a hoopdie 2006 Nissan Sentra with 160k on the clock. Runs very well, smooth and no abnormal noises. When I bought it the check engine light was on. I figured that was the O2 sensor. I changed the oil (ST) and filter; air filter; plugs; PCV valve. I need to drain fill the manual transmission and plan on replacing the upstream O2.

I have run about 600 miles on it. I use top tier 87 octane gas and ran a Techron fuel injector cleaner as well. I checked the gas mileage at last fill up (manually as this car is base and has none of the mileage toys to show you) and the hand calculation was 17mpg :unsure: This 1.8 should be getting 26/28+ mix driving. Unfortunately I did not have the smarts to check the gas mileage before changing any parts. It could be me not consistent at fill up or different pumps used (but it can't be that big of a difference).

Can a bad O2 sensor cause such a drastic decrease in fuel mileage?
 
Messages
3,859
Location
Chicagoland
Yep, if the upstream is lazy or reading incorrectly the PCM can try to adapt to make things “right.” When I replaced the upstream o2 sensor in my caliber my fuel economy went from 19-20 to 23-25.
 
Messages
10,965
Location
MA
Why don't you just figure out what the CEL code is and know for sure? Auto parts places check them for free and you can get a basic code reader for $5-$20. No reason not to know. I like to check what the codes are before even buying it. Worst case is that the cats are already shot.
 
Messages
7,271
Location
Roanoke Virginia
Yep could be the oxygen sensor but make sure and when you go to replace it make sure it has copper anti seize on it I’ve dealt with many stuck ones before it’s not fun.
 
Messages
10,965
Location
MA
I've had way more EVAP leaks on cars of a certain vintage than needed o2 sensors.

Regardless of whether you need them or not, if you change out the upstream sesnors when the mileage gets up there, you get slightly improved gas mileage and when they're in the $50 range, it probably pays for itself within a couple years or so.
 

BISCUT

Thread starter
Messages
3,082
Yep could be the oxygen sensor but make sure and when you go to replace it make sure it has copper anti seize on it I’ve dealt with many stuck ones before it’s not fun.

Went with a Bosch (17179) and it had anti seize on the threads with a plastic protector over the threads. Surprisingly the old sensor just needed a little bump with a rubber mallet on the stubby wrench (plenty of room) and it came loose.
 
Messages
7,271
Location
Roanoke Virginia
Went with a Bosch (17179) and it had anti seize on the threads with a plastic protector over the threads. Surprisingly the old sensor just needed a little bump with a rubber mallet on the stubby wrench (plenty of room) and it came loose.
Great usually they don’t come off that easy
 
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