My gas mileage is suffering and has been ever since I "modified" my catalytic converter. The Check engine light is always on and throwing downstream sensor codes. Everything else has been ruled out (new plugs, coils, pvc, air filter, IAC sensor cleaned, t/b cleaned, etc. I just didn't think the cat could have a negative effect on gas mileage since it is only the downstream sensor affected (which is not supposed to factor into the a/f or otherwise affect engine conditions). Is this not the case?? I'm considering throwing another stock cat back on, but figured someone could give me some real insight to my downstream sensor plight. Thanks in advance for any help.

 

I believe i have had a similar problem as you which was taken car of yesterday. I was getting a check engine for Bank 2 Sensor 2. The code was saying that there is high voltage going to the sensor. So i hooked up the consul (not the OBD-2) and monitered my real-time a/f ratios, and all the o2 sensors. That sensor was truly making mistakes and wasn't working properly. The graph was very unstable. I just replaced the o2, cleared the code and everything is good so far. But only 1 day has passed so i'm still skeptical. After I installed my y-pipe and cat i didn't reset the ecu for a reason, which was to wait and see if the car figures it all out on its own, which it did and threw the code. I was told to get an o2 simulator, but i haven't gotten around to that. So just check your real-time a/f ratio, and the o2's to see if it's really faulty. Hope this helps somewhat.

 

where can i get one of those simulators please???

 

o2simulator.com, or just google o2 simulators.

 

thanks! much appreciated

 

How did you modify your cat? and why did you?

 

He just changed his OEM to aftermarket, just as i have.

 

rear o2 sensor malfunctional

 

Funny thing is, rear O2 sensor should not effect gas mileage.

 

Could I buy one of these o2simulators instead of having my o2 sensor hang really low on my b-pipe