Ok, mits mighty max 1990 175,000 miles, i just failed the HC emissions section of my smog test, grrr, max is 131 i got 157. my check engine light comes on, but if i floor it ususally goes off, i think it's the O2 sensor, can someone confirm this, if so, does it rest in my air filter? and is it easy to change and is it cheap, cus friends . . . im broke

thanks

 

hoping that you are still on... your O2 sensor is on your exhaust.. normally on the headers.. (I think ALWAYS on the headers..) its easy to get to with a few hand tools and about 30 min.. cheap though... not sure with those, they can go from $50-$150 depending on what kind and all that jazz

 

Quick tip, change out the spark plugs and run one heat range hotter. That will lower the HC's, but may make the NOx rise(if they test for that in your area). Also make sure the Plugs are gapped correctly and are tightly installed. Also, i'm not sure if you can with the mighty max, but increasing the timing on the engine will generally bring down the HC's quite a bit, but will also make the NOx rise. Remember, HydroCarbons are unburned fuel, so general ignition tune ups and running the engine a bit leaner will help out. As for the O2 sensor, your's is probably starting to fail and since the ecu is sometimes not getting a signal from it, it reverts back to a base fuel map and retards the timing on the engine to make it run richer(and safer).