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Unread 09-04-2013, 12:19 PM   #1
Terry777
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O2 sensors when to clean and when to replace

I took out both O2 sensors and cleaned them, the down pipe one has been replaced at some time but the rear one looks like it`s the original from 1997 :]

After cleaning them I noticed while in sitting in traffic it idles a lot smoother sometimes so smooth I thought it stalled...

With that said the rear one has been there for many years and just cleaning the soot off made a noticeable difference, but would a new one give any better temp reading? I`m not techy with electrical and the wires don`t feel crispy or have any signs wear just the outside housing is as old looking as the stock muffler no doubt the original one from 97...

Not sure what that inside prong of the sensor is made of, ceramic ?

Thanks for your time, Cheers

Edit : Forgot to mention I reset the ECU.

EDIT : Worth mentioning sensor clean would be the preferred product as I`ve been told throttle body or carb cleaner may have chemicals that can harm sensors ? I haven`t had any issues yet but for long term once a year use I will be using the sensor clean...

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Unread 09-04-2013, 12:37 PM   #2
Terry777
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Thought I should add non of my O2 sensors looked like the damaged ones in the link, they looked like the one he`s holding beside the down pipe... scroll down a bit to see http://airflowmeters4cars.co.za/arti...ge-or-replace/
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Unread 09-04-2013, 12:59 PM   #3
V65Ozzie
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What makes an o2 sensor tick is inside, and I've never seen a way to actually clean them. They have a life expectancy of 80, 100,000 miles, after that they are recommended for replacement. By removing the soot you may have increased the flow through the parts that do the work.
An O2 sensor is actually a little electrical generator, it's amazing they last as long as they do given the enviroment they have to work in.
The insides consist of ceramic zirconia and platinum, oxygen reacts with these mediums to create a small electrical charge, the computer uses this charge to determine if the car is running rich or lean, more oxygen, more voltage, less oxygen, less voltage.
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Unread 09-04-2013, 02:50 PM   #4
JeeperCreepers7
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I literally just replace mine when they're throwing codes, it's never even occurred to me to replace them any sooner.
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Unread 09-04-2013, 07:29 PM   #5
Terry777
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I always thought they were more temp related then actually reading the oxygen. Just guessing if the air is low in oxygen it affects the temperature and vise versa.

I Googled under the image search and found some with the inners listed I`m just unsure if over the years the heat weakens them enough they don`t read right but not enough to throw codes.

Mine weren`t covered in soot, they had a very small almost unseen amount mostly the front one and I expected nothing to change, I used the straw on the can to soak inside the shell a few times... Made a huge difference for how clean they looked before I cleaned them...
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Unread 09-05-2013, 06:58 AM   #6
V65Ozzie
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Quote:
Originally Posted by JeeperCreepers7 View Post
I literally just replace mine when they're throwing codes, it's never even occurred to me to replace them any sooner.
Mine have lasted 200,000+ in both my ZJ's, but yes, they are an actual scheduled maintenance item. I replaced the rear one on my 97 last year, but that was because the harness dropped down and rubbed through on the driveshaft, it never worked properly after that. My 98 still has the OEM units, at 220,000 miles, however, I will be changing them soon, as soon as I repair that dang cracked exhaust manifold.
I see a lot of O2 sensors replaced that don't need to be, simply because of a code scan, no-one seems to understand exactly how to test them. My favorite one is the "Inefficient Cat" code. Chances are that if the O2 sensor is popping that particular code, it's working just fine, after all, it did figure out that what is coming out of the cat is outside the acceptable parameters compared to what's going in, it's the cat that's worn out,( incidently another item not designed to last much beyond 100,000 miles) Although, if you are replacing a cat, I'd recommend new sensors to go with it.
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Unread 09-05-2013, 11:38 AM   #7
vadslram
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They are somewhat temp related. They only work at higher temps. That's not a big deal since they are in the exhaust stream but if you have a 3 or more wire O2 sensor it has it's own preheater so that it starts getting valid readings sooner.
What kills them is stuff in your fuel. Different chemical additives will coat the sensor and keep it from working right. Carbon fluff just means you were running pretty rich in the first place.
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Unread 09-05-2013, 03:29 PM   #8
Terry777
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Cat pressure test ?

Is there a way to pressure test the cat to see how plugged it is?

It would be easy enough to plug the tail pipe with a gauge and take the reading at idle and a higher RPM to tell, no?

I have a clean used spare cat just don`t want to go through that again until the muffler gives, it`s close..
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Unread 09-06-2013, 09:23 AM   #9
Speedymcracer01
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If the cat is held on with u-bolts i just take the clamps off pull the cat and look threw it if i see light its still good. I'm not sure if there is a pressure test or not for the cat though i haven't heard of one if there is
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Unread 09-06-2013, 09:29 AM   #10
Speedymcracer01
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Quote:
Originally Posted by V65Ozzie View Post

Mine have lasted 200,000+ in both my ZJ's, but yes, they are an actual scheduled maintenance item. I replaced the rear one on my 97 last year, but that was because the harness dropped down and rubbed through on the driveshaft, it never worked properly after that. My 98 still has the OEM units, at 220,000 miles, however, I will be changing them soon, as soon as I repair that dang cracked exhaust manifold.
I see a lot of O2 sensors replaced that don't need to be, simply because of a code scan, no-one seems to understand exactly how to test them. My favorite one is the "Inefficient Cat" code. Chances are that if the O2 sensor is popping that particular code, it's working just fine, after all, it did figure out that what is coming out of the cat is outside the acceptable parameters compared to what's going in, it's the cat that's worn out,( incidently another item not designed to last much beyond 100,000 miles) Although, if you are replacing a cat, I'd recommend new sensors to go with it.
My rear o2 did the same exact thing to. It fell and rubbed the drive shaft until it was nothing but wires.i bet thats the reason my gas mileage sucks my o2 most likely is no good after that happened. I can't believe i didn't think of that
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Unread 09-07-2013, 09:44 AM   #11
Terry777
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Quote:
Originally Posted by Speedymcracer01 View Post
If the cat is held on with u-bolts i just take the clamps off pull the cat and look threw it if i see light its still good. I'm not sure if there is a pressure test or not for the cat though i haven't heard of one if there is
Easier said then done no doubt ?

Last time I played with a used exhaust system I had guys telling me it`s doable but not worth the time but I`m cheap and had lots of free time and got her done, with the help of my grinder to cut the pipes....

That said maybe worth a try for guys with new pipes and muffler but knowing defeat is probably the winner will help deciding when to relax put the hammer down and call it.
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Unread 09-07-2013, 11:15 AM   #12
V65Ozzie
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Quote:
Originally Posted by Terry777 View Post
Easier said then done no doubt ?

Last time I played with a used exhaust system I had guys telling me it`s doable but not worth the time but I`m cheap and had lots of free time and got her done, with the help of my grinder to cut the pipes....

That said maybe worth a try for guys with new pipes and muffler but knowing defeat is probably the winner will help deciding when to relax put the hammer down and call it.
You can't tell if the cat is good or bad doing that, unless it's obviously sooted up or melted. (Melted means that you are getting raw fuel into the cat, where it sits and eventually catches fire, I've seen a badly running vehicle set fire to the interior because the cat go so hot.) The problem is that the ceramic substrate has a coating of all kinds of very precious metals that react with the carbon monoxide, converting it to a mix of carbon dioxide, monoxide, H2O and oxygen(hence the name catalytic(catalyst) converter. You can't see how much of that coating is left on the ceramic substate(honeycomb).
You can do a back pressure test on a converter with a pressure guage, by drilling a small hole in front of the converter and seeing what the pressure reading are at different RPM's. Someone makes a guage that screws into the O2 port also. Pretty sure there is a chart floating around on the interwebs somewhere.
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Unread 09-09-2013, 08:41 PM   #13
Terry777
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Great info,
I was always under the impression the honey comb structure did nothing more than help the air become moist and it was the moisture that was the culprit that helped the emission's readings for the dinks or I mean Government...
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Unread 09-10-2013, 12:55 AM   #14
Speedymcracer01
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What is the correct voltage the o2 sensor is suppose to read? Around a year ago my 98 ZJ had bare wires showing after the wires where pulled down and rubbed the drive shaft. I didn't know until it blew a fuse,but im wondering if that could have affected the o2 's voltage reading? I taped the wires up real good,and tucked them behind the heat shield. It never threw a code,and still has no cel but it just doesn't seem to be running that great. It has bad mpg then the other day it seemed to of lost power when i took off from a red light it bogged down like it was about to die but picked back up with in a second or two and was fine. Just recently it has started idling a little funky the rpms constantly fluctuate between a few hundred rpms. I know it could be many different components that can cause this but i don't have funds for it. Do you guys think changing the o2 could help any of my ZJ's issues,or can i just check the volts to see if it has a good reading so i don't waist the money that could get something else for it?
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Unread 09-10-2013, 07:03 AM   #15
V65Ozzie
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Quote:
Originally Posted by Speedymcracer01 View Post
What is the correct voltage the o2 sensor is suppose to read? Around a year ago my 98 ZJ had bare wires showing after the wires where pulled down and rubbed the drive shaft. I didn't know until it blew a fuse,but im wondering if that could have affected the o2 's voltage reading? I taped the wires up real good,and tucked them behind the heat shield. It never threw a code,and still has no cel but it just doesn't seem to be running that great. It has bad mpg then the other day it seemed to of lost power when i took off from a red light it bogged down like it was about to die but picked back up with in a second or two and was fine. Just recently it has started idling a little funky the rpms constantly fluctuate between a few hundred rpms. I know it could be many different components that can cause this but i don't have funds for it. Do you guys think changing the o2 could help any of my ZJ's issues,or can i just check the volts to see if it has a good reading so i don't waist the money that could get something else for it?
IIRC, there is not a constant voltage, so it's tricky to explain. Go to buzzle.com and google how to test an o2 sensor, they have a pretty good explanation.
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