Cat Conv & O2 Sensor questions

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Cat Conv & O2 Sensor questions

Postby RobsZRinAR » Fri Feb 27, 2015 10:11 am

Hi all. As noted in my intro post, I recently bought a 2003 ZR5 CC that I'm loving!
Yesterday, I had the Cat Converter replaced after chasing codes all over the place. SES light is off :D and she has more power! 126K miles.
As it is a new-to-me, I would like to get certain things squared away so that I have a base point for future ref. I've replaced plugs and wires, cap, and checked rotor. All good. I have found some deteriorated vacuum lines that will be replaced this weekend. I would like info on how to identify if my O2 sensors are stock. Is there a way to tell?
Previous owner obviously took great care of the truck but kept no service records.
Pics will come soon. We have a bunch of white junk all over that just won't seem to go away. It makes a mess of a Black truck. :x
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Re: Cat Conv & O2 Sensor questions

Postby ApproachMedium » Tue Mar 03, 2015 12:30 pm

It has always been my assumption that the O2 sensors will give you a fault when they are bad/not working right. If the cat was just replaced changing the sensor behind it might not be a bad idea but if there is no CEL for the P0420 code now then it should be okay. Some say that after so many miles you should just change them.
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Re: Cat Conv & O2 Sensor questions

Postby HenryJ » Tue Mar 03, 2015 2:54 pm

Deposits do degrade the performance with time. The owners manual recommendation is 100k miles IIRC. I replaced mine around then.

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Re: Cat Conv & O2 Sensor questions

Postby LoneWolf04 » Tue Mar 03, 2015 7:21 pm

I replaced my sensors around 80k when I replaced the cat. The other thing I did was replace the fuel injector to the updated unit. Mainly because unburnt fuel will severly damage the converter and stuck poppet valves will directly cause this. Didn't want my brand new converter being subjected to a part known to fail.
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Re: Cat Conv & O2 Sensor questions

Postby OrlandoSonomazr5 » Sat Mar 21, 2015 11:12 am

how many o2 sensors are there I've been contemplating a Cat-delete to run some race fuel, but haven't looked to see if there is one before and after the cat or not.
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Re: Cat Conv & O2 Sensor questions

Postby ApproachMedium » Sat Mar 21, 2015 11:20 am

All OBD 2 cars have one after the cat. The S10 has 3 o2 sensors two upstream after the exhaust manifolds and one after the cat.
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Re: Cat Conv & O2 Sensor questions

Postby OrlandoSonomazr5 » Sun Mar 22, 2015 11:43 am

Are you sure all OBD2 vehicles have 2 O2sensors one before and one after the cat?? Cause I've owned Nissan's and other Chevy's with strictly one after the manifold, but they were either turbo Japanese import or LS Vette motors, so I'm not sure if that plays a role in the dept we're discussing. That's why I ask.

With those I was able to just purchase downpipes that were cat delete downpipes 3" from the turbo back and only ran one O2 sensor so the motor never had issues or got confused trying to read two O2 sensors sending the A/F readings off causing a check engine light and bank errors.

I also believe the last LS6 engine I had in my RX7 was only two sensors one on the left exhaust bank, and one on the right bank.

Only reason I ask is cause I've got a exhaust leak under the driver/passenger door and I believe its where the y pipe meets the cat. Haven't really looked at it so not sure what it looks like under there. But If Something majors wrong I'm just gonna have a custom exhaust done and was hoping to ditch the cat. But if there's two O2 sensors then that means playing with the computer and I'm not going that route.


Even though Im in Florida This truck came from the Jersey Shore where I used to Live. Noticed in your profile info your location. I grew up in Forked River.
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Re: Cat Conv & O2 Sensor questions

Postby ApproachMedium » Mon Mar 23, 2015 12:46 pm

There are ways to delete the O2 sensors without using the computer for the one after the cat. I think there is a resistor pack you can add so that it sees the proper reading all the time.

Pretty much any OBD2 (1996+) car I have dealt with has one before and one after. The one before controls engine fuel output etc the one after the cat just tells the computer if the cat is working properly or not. This is why in NJ they dont need to stick that thing in the tail pipe at inspection on a car thats 96+ because the car technically does the work for them with the sensor after the cat. Omissions of these things on specialty high performance cars like the LS in the vette is possible, I havnt dealt with one of those cars before. Just regular everyday stuff.
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