4.8 mpg no catalytic converters

[Roy450]

Hi guys,

 

I have a 2003 Silverado 4x4 with a 4.8 and 3.73s and auto trans. My catalytic converters were very plugged up and I ended up cutting them open, removing all of the material inside, and welding them back together. The truck has run much better since doing this. The problem is, since doing this i have been getting about 13.8-14 mpg with it. This is driving the same route i had been getting 16-17mpg previously. I am thinking that this has something to do with the fact that i left the o2 sensors in place. I am looking for a relatively inexpensive fix/ improvement for this, because this is just a rusted out daily driver truck with 160k that I don't really want to put a ton of money into. I wanted to see if anyone had any experience with this before I tried a few of my ideas. Any advice would be appreciated. Also, i am aware that this is technically illegal, but there are no emissions tests in my state, so running no cats is not a huge issue for me.

 

thanks 

[Colossus]

My thought:

Have a tune done that will delete the O2 sensors and Cats from the configuration as far as engine computer goes.   You can likely improve performance and fuel economy via a tune as well.  Not sure if this is something that Blackbear can do, but they are my top pick when it comes to aftermarket tunes. 

[Colossus]

If you want to keep the O2 sensors on there for emissions purposes, then the original O2 sensors are going to be very tired and worn out by now even though they may not set a check engine light.  There will be 1 or 2 O2 sensors before the CAT but I can't remember if that gen of 5.3L & 4.8L has one or two after the CAT as well.  If there are after the CAT, those need to be eliminated from the computer programming for sure if you are running gutted cats. 

[Roy450]

Thanks Colossus, 

I was thinking of maybe getting some spark plug defoulers to move the o2s after the cat back out of the main exhaust flow. I know that others have done this before and had good results. I am not bothered at all by the check engine light being on. It has been on as long as I have owned this truck. Just looking for a cheap improvement as the body of this truck is in pretty rough shape from being in Michigan its entire life. Just don't want to put any more money into this truck than I have to.