So I decided to replace my old cat setup that I suspected was some form of high flow setup since the attached head pipes were mandrel bent and all but full of cracks and holes....

Anyway I discovered the previous owner had completely hollowed the old cat out....
Upon installing my new #23285 magnaflow converter and #1 o2 sensor I found the 02 sensor after the cat is more stable and even I also found my long term fuel trim level now dropped from around 14% to fluctuating from around 5 to 2% after warm up on a 2 mile drive.... The truck also seems to have more low end grunt.
I did notice its slightly quieter when I rev it now though. although that may be from me sealing up all the exhaust leaks from the old pipe.

I'm curios to see how my gas mileage is effected

 

kudos big AD!! Keep us updated.

 

what do you mean by AD?
lol sorry did you mean Augiedoggy?... I'm slow I guess...lol

 

AuggieDoggy

 

Its kind of odd that I got no error codes from the o2 sensors with not guts in the cat? they were functioning from what I could see in torque monitoring software.

 

O2's are finicky sensors..

Not only do they sample air inside the tubes, but outside as well.. that is why there is a voltage difference, as it corresponds with the contrast between interior and exterior.. if the outside of an o2 sensor is fouled with grime, oil, grease, or God help you antifreeze, you're not going to get true readings.. the pcm doesn't know this, because its looking for differences as opposed to similarities.. similarities is what they want.. if the sensor reads similar o2 content on the inside and out, it thinks its doing a marvelous job.. and, you don't get a code.. if there are differences outside parameters, it will kick a code.. if there are subtle differences, it makes adjustments to your a/f.. the upwind does a lot more a/f adjusting, but the downing has play in it too, just not as much.. grime on those things isn't a good thing..

 

well the old ones were pretty clean..I only replaced the upstream one with a borg warner replacement... I did notice the olde ones were two different types as far as the sensor shields...
I was surprised they had very little buildup on them just an ever so slight light coating that was barley there on half directly in the air stream...not even enough to really notice when wiping with a clean cloth.

 

On a lot of cars the O2 sensors are used to determine whether you are running cruising or accelerating; if it senses you're cruising it adjusts to closed loop mode and runs the fuel rails a bit leaner for economy. Since the cat wasn't plugged (obviously) and they both seem to be working (not fouled)then it wouldn't see a differential there, so I'm not sure what else, if anything, could trigger a code.