so ive replaced the precat o2 and HUGE difference, but can still hear it sucking air a little and seems to be running rich and a little worse on gas than it should be... any ideas?

 

Have you tested the sensors in the throttle body? How is your plenum gasket?

 

How do you figure it's running rich? Do you have a missfire?

 

it has a slight miss but you can smell it in the exhaust. and i just recently replaced the plugs, wires, cap and rotor (maybe 500 miles ago). Almost seems like my precat o2 sensor is getting messed up again and i just replaced it about 2 weeks ago

 

It's quite likely, actually. Did you replace it yourself? Those O2 seonsors get so fused in the pipe that you are running the risk of stripping the thread when removing. When I replaced mine (i have 2 of them) we had to weld the old wholes shut and drill/install new threads...

But you can always unplug the O2 sensor just to make sure the misfire would disappear. If it doesn't then the problem is somewhere else.

A lot of people think they got a bad sensor (which is possible) or that Bosh sensors are junk, because they don't realize they've messed up the thread. If you have your old sensor, take a closer look at its thread. And if you bought the new one from a B&M shop, they have 1 year warranty - replace it.

 

i did replace it myself and it came out quit easily actually, and the threads were fine... i put it in about 2 weeks ago... it cant be bad already lol

 

Well, the easiest way to find out if the O2 went bad is to simply unplug the sensor and see if it makes any difference. Sometimes you can indeed buy a junky one

 

It is possible it's bad. Just like any product you buy from anywhere, they are built or designed by human beings, there will be new out-of-the-box failures/dead units. Nothing's perfect.