I wanted to double check with someone knowledgeable in the area of o2 sensors in our cars. It is my understanding that all of the fuel trim is controlled by the primary o2 sensors and the secondary are only there to make sure that the catalytic converter is doing its job. Is this correct?

 

I beleive 2 sensores are pre-cats, and 1 is after-cat, why?

 

well.....it wasn't to long ago that I had both precats fail and instead of putting headers on or replacing the precats I just gutted them(and noticed hp gain) and spaced the secondary o2 sensors out from the exhaust stream using spark plug nonfoulers to avoid a check engine light. I just wanted to make sure that by doing what I did I am not hurtin fuel economy in any way adn that my car is still running the best it can.

 

2 are after-cat in our cars.

 

Yes, sorry, you are correct, there are 4 sensors total, 2 pre-cats, and 2 after-cats.

 

yes there are 4 total. I am just curious if anyone knows whether or not the 2 after the cats have anything to do with fuel trim? I recently gutted my cats and it seems like my car is running rich.

 

Im wondering this myself. I did the same thing you did and for a while I was getting ses lights daily and after like a week of reseting them they just stopped. I also find this weird because I have an aluminum plate blocking off my egr valve and it even seems to not pop a code for that any more

 

Well I gutted my cats and installed a racingline ypipe along with o2 sensor spacers and magnaflow mufflers. I dont have as ses light but am wondering if I should get an air
/fuel controller. Will a VAFC II work with our cars? or does it need to be an Safc II?