O2 sensor pathy 2001

[billd6373]

O2 sensor did not read at emmision test fuel consumption a lot more than usual can I tell which of the two pre cat sensor without code
(not pulling any codes at this time) already replaced MAF and TPS
Thanks in advance for any help 2001 pathfinder

[Towncivilian]

Welcome to NICO.

Have the engine codes pulled at an auto parts store such as AutoZone and post them here.

[billd6373]

for some reason there is no code The mechanic doing the emission said the pre cat sensor would not read but could not tell which which of the four to replace

[Towncivilian]

Is your "SERVICE ENGINE SOON" light on?

[billd6373]

NO but the light went out after I replaced MAF

[Towncivilian]

If the upstream sensor was failing, it would throw a check engine light. How many miles are on this Pathfinder?

[billd6373]

115K im getting only 10 mpg I used to get 15
When I try to rev engine to heat up sensor the engine sputters , but in gear I have no issues

[Towncivilian]

Have you changed the spark plugs around 105k? Is the fuel filter recent?

[billd6373]

just replaced fuel filter /replaced one plug per ses light when I first got it 2 years ago

[Towncivilian]

You only replaced one spark plug?

Try running some fuel system cleaner containing polyether amines, which is a chemical proven to clean deposits without leaving behind its own residue (SAE paper detailing PEA). Products which are known to contain PEA are Chevron Techron, Gumout Regane, and Redline SI-1.

[billd6373]

it was the only one throwing a code
would cleaner affect engine not responding to reving

[Towncivilian]

It might help somewhat depending on what exactly the problem is. Did you replace only one spark plugs, or all six?