Posted on this a while back but didn't get any responses so I'll try again. Does anyone here know of the correct spacing for the o2 sensors and the CAT? I want to rework my exhaust, but even cars of the same year, my being a 95' have either 1 o2 sensor way up stream, or 2 sensors. One infront of the CAT and one behind. Are there critical spaces? Thanks!

 

Pardon my ignorance but couldn't you just take a look under your truck?

 

My exhaust has been radically changed. Its in my sig. Anyways, while it was fun for awhile to have it downturned right under the floor, I have grown tired of the noise and wish to reroute it out the back further. I have been having fuel milage issues, and the only code that has come up was a lean condition. My o2 sensors tested ok, but I have noticed a change in mpg since I "customized" the exhaust in the first place. As far as I know, if the computer sees a lean state, it richens the mix to keep the exhaust valves from burning. Any ideas?

 

Is your cat plugged? Newer trucks have been known to throw lean codes with plugged cats because they aren't allowing good exhaust flow so the mix is messed up in the cylinders due to the exhaust not moving out. Anyways just an Idea.

 

Spacing between sensors and cat is not critical, just need:
a) the front O2 sensor downstream of the exhaust manifold or header collector, so it averages all the cylinders.
b) long enough wiring to the O2 sensors
c) don't place the sensors so close to the cat that you melt the wiring. Six inches away will usually suffice.

 

Nope, the cat is new.
I do remember Downey had some specs to the "proper" dimensions. You're saying the spacing is not inportant ? Also, this might sound wierd, but how do you know which direction the cat should go?

 

Aren't cats and mufflers stamped with a big arrow indicating direction of flow?

'Proper' dimension is only to make sure your wiring harness isn't too short so as to require an extension cable, and not too long so as to have a bunch of loose wire dangling about the hot pipes. Just locate the front sensor someplace between the collector and the cat.