Question about O2 sensors

WeaponX

Original poster
Member
Mar 23, 2019
212
Pittston, PA
I’m putting in the new car pipe and I bought new upstream and downstream O2 sensors.
Well the new one to go into the pipe won’t be an issue to install but I can’t budge the one in the manifold AT ALL (and may have riffed it up a bit trying to get it off)!
So my question is is it imperative to replace both of them if you do one or as long as I have no more codes (which I do but I’m assuming for now it’s just cause I cut the old clogged cat out and put a pipe in-line) then it’s ok if one is old and one is new?
Thanks guys
 

Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
Unless you are having issues, you don't have to replace it.

BTW, the post-cat sensor only reports to the PCM if the cat is working or not. Does nothing for performance or running of the engine so we don't bother with it unless it is defective.

Did you try getting the engine good and hot? That usually helps to get it out of the manifold. Could also try heating the manifold around the sensor with a propane torch. If that doesn't work, may have to take it to a shop and heat the manifold with oxy torches.
 

Maverick6587

Member
Dec 16, 2018
730
Sterling Heights, Michigan
I think @Blckshdw kept spraying penetrating fluid on it for 2-3 days. While also driving it to work and getting it hot, before he tried to pull his O2 sensor out.
 
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Blckshdw

Moderator
Nov 20, 2011
10,665
Tampa Bay Area, FL
Yep, sprayed it on a Wednesday and Thursday night, normal commute Thursday and Friday. Attempted to crack it loose Friday night, to see if I should spray it again for a Saturday morning swap, and it cracked loose without too much fight. I used the O2 sensor wrench, and breaker bar combo. I sort of wish I had both the wrench AND socket, cuz it was annoying trying to reposition the wrench to get consecutive turns out of it. It was too tight to spin by hand, but a ratchet would have worked great.
 

Maverick6587

Member
Dec 16, 2018
730
Sterling Heights, Michigan
I've heard that you are not supposed to use anti-seize on O2 sensors. Is that true for GMT-360 O2 sensors? My ACDelco O2 sensor came with anti-seize, or what looked like anti-seize on it already.
 

Blckshdw

Moderator
Nov 20, 2011
10,665
Tampa Bay Area, FL
Considering how they can get rusted into the manifold, and cause such a battle to remove, I can't see why you shouldn't use any. My replacement came with anti seize (all over the damn place) as well.
 
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Maverick6587

Member
Dec 16, 2018
730
Sterling Heights, Michigan
I had to go look at where I heard that from and I got it backwards. Anti-seize is ok to use, just make sure it's rated for an O2 sensor. You are not supposed to use dielectric grease on the connector though.

I watched this series to be more familiar with air-fuel ratios and how they work. It's a long video but, well worth the watch if you're interested in how the O2 sensor works.

They point out the answer to the dielectric grease question at 58 minutes if you want to cheat.
 
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