downstream o2 delete?

[Rootie524]

i will be doing some exhaust work. part of my concern is the o2 sensor. i mean it would be no big deal to weld a new bung in my exhaust but if i dont have to, then i won't.

i know the upstream o2 determines fuel trims. but as far as i know the downstream only determines the efficiency of the cat, and no matter what will never alter fuel trims, therefore rendering it useless to me.

so am i right in saying i dont "really" need it.

[pocket-rocket]

I've read it does play a part in fuel trims, but a very very small one. Also, if you have emissions testing and inspections, you might want to keep it. If not, you could get a rear O2 simulator to keep the PCM happy without removing it from the programming.

[robertisaar]

i've never heard of the past-cat O2 sensors effecting fuel trims.... the catalyzation(?) that occurs would skew the sensor readings, kind of like how a tailpipe wideband O2 at a dyno isn't always accurate if a cat is installed.

[pocket-rocket]

I was going by what I've read on the interwebz. I know not everything on the internet is true (you mean Elvis really isn't alive?! ), but we do agree that it's not a necessary piece of hardware.

[Rootie524]

yeah but it determines the efficiency of the cat. so if it notices a huge difference of what it's supposed to be i suppose its possible it would slightly alter fuel trims. we need a third party vote to settle this one.

[Superdave]

just for the cat.

o2 sims are harder to come by these days, one thing that people have success with is installing spark plug anti-fowlers between the o2 and the pipe. It kind of skews the o2's readings so that it's not the same as the upstream and helps to keep a consistent voltage.


A Sim wouldn't be hard to build, i've been meaning to put one together with common parts so i can get rid of the CEL on my truck (gutted cats). Someday i'll get to that...probably fairly soon.

[Rootie524]

would another way to just turn in off with hp tuners. i know i can at least make it so the engine light doesnt come on..but somewhere else, it still is reading a voltage so it might throw it off. i assume there must be a way to tune it out in the pcm.