So will fuel milage improve or get worse?

 

read all of page 1?

ok just in case...rich means more gas consumed, means mpg goes......down

 

Why would it run rich? The rear o2 sensor has nothing to do with the morot/fuel. All it does is throw a cel when it thinks the cat is bad. The front o2 is what controls fuel. If you remove the cat the front o2 has no clue so it doesn't change anything.

 

This was to thought to be true, but it has recently come to light that the rear o2 DOES have at least some bearing on fuel trim. There is a window that the emmisions are to be at, and the front and rear o2's communicate back and forth and adjust fuel trim to try and keep within this window. With the cat gutted or removed you are removing the "filtering" and it will run rich to try and stay in the operating window.

My cat is gutted and get a CEL for it. When I clear the code I can tell better responce from the engine and better mpg. When the light is on, my milage goes down by about 20-30 miles per tank. Depending on how I drive, I'll get 220-250 miles per tank without the CEL. When its on I drop to 200-220 miles. And BTW, I fill up at 1/4 tank, or try to at least.

 

I wont be gutting mine then. My truck only geys 9mpg now

 

If you do the non-fouler trick, then you dont need to worry about it. It'll fool the readings and the PCM will believe everything is within spec.

 

I just replaced a gutted cat with a high flow and I use the torque application to monitor all my feul trim and o2 sensors reading and such and I can tell you my truck uses less gas and the fuel trim numbers are totally different now...
I wasnt getting any codes from my post cat 02 sensor either...
the cat gets super hot and actually creates negetive pressure to pull gases from headers and aid in scavenging effect....on my truck the cat is the y pipe...I got the stainless magnaflow #23285 kit with pipes to headers and to muffler for 189.00 shipped and it has better than oem mandrel bent pipes...It took about an hour to replace (bolt in). high flow cats for the newer98-2001 rams are like 69 bucks....The whole cost thing really shouldnt be a factor.... Honestly, if it is, I suggest you get a more fuel efficient truck and then you wont be so broke...

 

If you are only getting 9, on a basically stock truck, you need to find out why......

The non-fouler trick fools the PCM into thinking the cat is still there, and everything is hunky-dory. No decrease in fuel economy, a slight pickup in power. (very slight.)

 

Do you think perhaps that just putting better flowing pipes in there weren't the major contributors?

 

Nope, because the original exhaust I replaced was also mandrel bent performance setup, not OEM.... This one just had guts in the cat, otherwise it was the same. I also had a noticable increase in low end getup and go...nothing major but noticable. Plus better flow doesnt always mean more power... If it did these trucks wouldnt run terrible without an exhaust right? That boils down to that whole pulsing scavenging effect people often mistake for backpressure..
I've read opinions both ways that the post cat sensor does and doesnt effect mileage.... also seen videos on youtube from various shops stating it does effect things... perhaps on some cars depending on the programming it does?