O2 sensor , to put back or not

[Chrisdied]

Guys I cut my cat off , right where it goes from the headers to the original cat. Removed the cat, installed a y pipe , then 2.5 tubing back to a cherry bomb muffler that dumps to the floor right at the end of the cab. Sounds good but I'm loosing gas mileage , down to 5mpg , I left out both o2 sensors to see how it ran. What have you guys done with the sensors ? Should I put the post cat one back in ? I saved the old tubing so I can reuse the bungs. Some info would help thanks I was getting around 10ish before , I also have 35in tires on a stick rear end I believe 3.73s or 3.55 I forget which

 

[MagSport]

Guys I cut my cat off , right where it goes from the headers to the original cat. Removed the cat, installed a y pipe , then 2.5 tubing back to a cherry bomb muffler that dumps to the floor right at the end of the cab. Sounds good but I'm loosing gas mileage , down to 5mpg , I left out both o2 sensors to see how it ran. What have you guys done with the sensors ? Should I put the post cat one back in ? I saved the old tubing so I can reuse the bungs. Some info would help thanks I was getting around 10ish before , I also have 35in tires on a stick rear end I believe 3.73s or 3.55 I forget which

3.55s and you should put the pre cat back in. You can leave the post cat out.

 

[dapepper9]

Pulling the precat throws the pcm into a closed loop and runs it rich.

 

[MagSport]

Pulling the precat throws the pcm into a closed loop and runs it rich.

Thought it ran in open loop then?

 

[dapepper9]

Thought it ran in open loop then?

No pretty sure it runs it at a set fuel level that's kinda rich.

 

[dodge dude94]

Open loop = PCM defaults = PIG RICH

Closed loop = PCM reading off O2 sensor


You got the terms backwards, Peppy.

 

[dapepper9]

Dammit

 

[Merc225hp]

3.55s and you should put the pre cat back in. You can leave the post cat out.

******** it also needs to be in play.

 

[MagSport]

******** it also needs to be in play.

Why? The post cat is only used to determine how much catalyst is in the system right? If he doesn't have a cat then is there not a point in having it?
Also welcome back Merc!

 

[dapepper9]

Why? The post cat is only used to determine how much catalyst is in the system right? If he doesn't have a cat then is there not a point in having it?
Also welcome back Merc!

I thought at cruising it affected a/f ratio

 

[MagSport]

I thought at cruising it affected a/f ratio

I always thought that was the precat's job. In closed loop the motor reads off the pre cat and the post is solely for the cat, Or so I thought.

 

[dodge dude94]

They work in conjunction to determine AF/R. Some guys can make em work without the post-cat, but it's SOOO much easier just to run it as well.

 

[joshputman]

For the post cat sensor, buy two spark plug non foulers. Drill one out to 1/2". Screw the sensor into that one, then screw that into the untouched one.

Finally, screw THAT into the ****. It fools the sensor into thinking the cat is working, and keeps you from getting a check engine light.

Artificial intelligence will never beat natural stupidity.

 

[dapepper9]

^^only worry about that if it throws a code