Thanks for sharing your experience. Wouldn't the heater element built into the O2 sensor prevent small temperature changes in the exhaust caused by a hairline crack in the manifold?

 

the heater is just there to get the sensor to its working range faster. it really doesnt do anything once the car is warmed up. but the temperature changes affect the cat more than the sensor.


this is getting a little complicated. lets start with the seafoam, then see what happens. ph, and try to drive around for an hour or two after using it, before you get to the smog check. theres no telling what that stuff would do to your results if you are still burning it off.

 

You said your car doesn't warm up to midway well try to replace your thermostat because if you engine doesn't warm up then everything won't work as its supposed to.

 

Yes you will fail the tailpipe sniffer test if the engine does not fully warm up.

 

but if hes failing on NOX, then any extra heat is going to make it worse. as long as the cat is lit off, its hot enough. and if it wasnt, the problem would be HCs and CO, not NOX.