Can a dirty air filter cause high HC? my test was just above the max on the 1500 and 2500 RPM test.The smog tech said to change my air filter and come back the next day.I changed the filter ,it was quite dirty.Cant make it back til next week though.I have no check engine light and the truck runs smooth.Any help out there?Its a 98 montero sport 3.0L w/ 198k miles.Thanks.

 

hmm, i've run with dirty filters and pass fine. I would suspect maybe something else. hows the cat and o2 sensor? thats what I would suspect.

 

Dirty anything when going before the SMOG Gods is not a smart thing to do, at least out here in the People's Republic. High hydrocarbons in your score translates into unburnt fuel making it out your tailpipe. So why are you running rich? Is your O2 sensor shot and so your ECU is getting false mixture information or do you have an oxygen leak and so you're running lean and your ECU is overcompensating? Or is your cat dead and so can't clean up your act? Is dirty oil adding to your HC woes? Are worn rings adding extra oil into your gas/air mixture? Or is it like your tech said, that a dirty air filter is starving oxygen from your air intake? That's certainly the cheapest thing to fix, but just be aware of all the factors that can contribute to your worrisome SMOG readings.

RTE is right and gave you two areas to check up on if a new air filter brings you no joy.

 

Can anyone tell me if the rear (downstream) O2 sensors are identical mechanically other than the connectors being different?Ive read where I need Bosch 13801 (two required).Ive also researched and found different part #'s for the left and right.

thanks

 

Some poster (thewelder?) on another thread said that the rear sensors only measure whether your cat is working and don't affect fuel mixture like the two pre-cat ones do. Whether this means that they are therefor non-interchangeable I don't know for certain. I do know — as you state — that they call for different part numbers, so I'm assuming (never wise, but I do it all time myself) that they are mechanically different in some way, unless that designation only differentiates the length of their connecting wires while the sensors themselves may well be identical.

Time for the peanut gallery to chime in with something more concrete...