Car question - Oxygen sensor.

[The Buddha]

The Mixy bixy we got seems to be eating O2 sensors.

Now the originals lasted 150K and 10 years. We replace with a "standard" brand as opposed to a "NON Standard" that was in the car. and its eaten the second one in 6 months.

So is it a case of crappy O2 sensor - and are there brands known to be garbage ... and what isn't, and please dont tell me the $300 one is good, and the rest are all garbage.

If an O2 sensor fails - what fails in it - the heater coil ?

Cool.
Buddha.

[codajastal]

O2 sensors must be heated up by an electrical power source in order to survive the stream of hot exhaust gases. That's the ECU's job to provide the proper amount of current in order to keep the sensor hot while the engine is running.
So, I'd start by verifying that the 02 sensors do get hot when the engine is running.
Obviously, this can only be properly verified when the exhaust pipes and engine are cool to the touch.
You can start with the rear 02 sensor:
- take it out of the exhaust pipe and keep it connected to the harness
- only let it rest on a surface that can resist heat and fire (concrete slab of your garage floor or street pavement)
- start the engine
- wear heat resistant gloves and try to "feel" if the 02 sensor is getting hot (be careful; it may get VERY HOT)
- if it's not getting hot then there maybe something wrong with the ECU or with some relays connected to the ECU


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[codajastal]

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Automotive News

Oxygen (O2) Sensors

Oxygen sensors use to be just another sensor that you only replaced when they went bad. Over the past few years Oxygen sensors have become a tune-up component. Most O2 sensors now have a recommended replacement interval, which varies from vehicle to vehicle. Most O2 sensors should be replaced between 30,000 and 50,000 miles. Check your maintenance schedule in your owners manual for your particular vehicle, or call your local auto repair facility.

What does an O2 sensor do?
An O2 sensor uses voltage to read the oxygen level in the exhaust and then send this information to the vehicles computer. The vehicles computer (ECM) uses this information to control the amount of fuel the vehicle uses. Not only is the amount of fuel consumption important to the way the vehicle runs, it is also important for proper catalytic converter function. Too much fuel can cause the catalytic converter to get plugged up, which in turn can cause severe engine damage.
Will I know if I have a bad O2 sensor?
Not necessarily. Most people won't notice the symptons of a bad O2 sensor because it deteriorates slowly over time. According to Undercar Digest, "Over time and thousands of miles, performance of O2 sensors can deteriorate even if they appear to be still functioning." Some of the symptons of a bad O2 sensor could be increased fuel consumption, rough engine performance, higher emissions, engine spark knock, and fouled spark plugs. A bad O2 sensor may or may not cause the "check engine" or "service engine soon" light to come on.
What causes an O2 sensor to go bad?
According to Undercar Digest, "...the intense heat in a vehicle's exhaust system eventually takes its toll. Physical damage, such as a cracked or broken element from impact or thermal shock, or simple heater-element failure can make a sensor inoperative. But other than physical damage or simple age, contamination is the primary cause of O2 sensor failure. Contamination can come from:
Silicone from an incorrect type of RTV sealer or antifreeze leaking into a cylinder
Phosphorus from burning oil
A blown head gasket
Spilled oil on the sensor
Rustproofing or other chemicals sprayed onto the sensor
Harmful fuel additives such as injector or carburetor cleaners
Anything that blocks the outside air-vent supply source"
As you can see, there are many reasons an O2 sensor can go bad. If you suspect you could have a bad O2 sensor, either have your system tested or have the O2 sensor replaced by a qualified technician.

Why should I pay a qualified technician to replace an O2 sensor?
There are a number of different types of O2 sensors used on vehicles today. Whether it is heated or unheated, single wire or multi wire, planar or wideband, the correct sensor must be installed during replacement.
Some vehicles have only one O2 sensor while other vehicles can have 2, 3, or 4! They must be tested to find out which one or ones are bad. However, understand that if a vehicle has more than one O2 sensor, it is always best to replace all of them at the same time. Since they were all made and installed at the same time, there is a high probability that they will all go bad at about the same time.
Undercar Digest states, "...be aware that because of the intense heat and continual exposure to moisture, the old sensor is likely to be rusted into the exhaust system and difficult to remove... Extracting it may require some real work or a torch. In some instances, removing it can strip the threads in the exhaust pipe, and you may have to introduce new threads in order to screw the new sensor into the system."
If your "check engine" or "service engine soon" light is on due to a bad O2 sensor, it might have to be shut off using a computer scanner.
If you have any questions regarding Oxygen sensors that were not covered in this newsletter, feel free to email us. Please do not email us regarding troubleshooting or diagnostic procedures. We recommend leaving that up to the repair facility you use.
This article provided in part by Undercar Digest.



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[The Buddha]

Its following that sensor, its not any other part of the car.
Wherever the "new" sensor is is what it doesn't like.
Cool.
Srinath.

[Old Mechanic]

I think my 17 year old Ranger still has the original 02 sensor at 129k miles and the last tank of fuel got me 33.6 MPG. By the time you see a code assuming your car is newer than 1995 you will have seen a gradual deterioration in fuel mileage, up to about 25% before the OBD2 kicks any code. Single wire 02 sensors are not heated, they just generate a voltage signal based on the oxygen content of the exhaust and the ECU uses that voltage signal to adjust the fuel mixture. The post converter 02 sensor is there to check the function of the catalytic converter, it is not directly involved in fuel mixture trim through the ECU like the pre cat sensor.
Oxygen sensors can be contaminated by any silicone sealer or other things like over oiling a K&N filter.
If you have OBD2. it should give you a CEL (check engine light) and a code for the detected malfunction.
I prefer to replace things when I can see evidence of their failure. At 30k per replacement I would be on the 5th 02 sensor on my truck which is a lot of money and I guarantee you it would not get better mileage.

regards
Mech

[The Buddha]

This is a 4 wire sensor. With the way my wife drives ... I cant notice a deterioration in anything ...

Last month the water pump gave up mid intersection, and made a huge rattling noise and she pulled over as soon as she went through the intersection etc etc ... as I was talking to the mechanic waiting for the tow truck. My mechanic asked me if the timing jumped and if it hit valve to piston etc ... I told him, I dont think valve hit piston, cos with the way my wife drives you know that baby'd be launched through the hood if it did ...

It sill hurts where the little woman elbowed me.

Anyway, she's a regular Danica Patrick+Angelle Savoie rolled in 1. Captain leadfoot. I just pour it and floor it. I think this michu bichy needs a nice wing, I can really pick up 2-3mph on top. What Kind of race slicks should I run on my Michubichy for getting the best handling so I can run full throttle through our hood and not slow down round the corners.

Cool.
Srinath.

[codajastal]

Sounds to me you need not be too concerned with continually changing it. Just leave the shitty one in there as the only damage will be to your pocket?

[pliskin]

Here is a tip. Take it or leave it. Most modern cars have two 02 sensors. One before the cat and one after the cat. If your car is giving a check engine light or 420 code you will start burning trough sensors. Factory sensors will last longer but not as long as the original sensor. Aftermarket sensors are crap. Do this...put a spacer between the sensor flange and exhaust mount flange. This will get the sensor out of the direct path of the exhaust flow. The sensor is measuring the differences in O2/fuel as it passes through the cat. It will through a code if the readings the computer takes fluctuates to much. Removing it from the flow will keep the check engine light off. The object is to get the sensor (usually the one after the cat) out of the exhaust flow.

The sensor before the cat will read ups and downs in the fuel air mixture and the computer knows this. The one after the cat should be reading much less fluctuation because the cats job is to burn off the leftover fuel. If the sensor after the cat detects to much fuel your cat might be out of spec but not clogged.

FYI, I have read that modern cars do not need cats. The computer controlled electronic injection takes care of the fuel/air mixture. Catalytic converter actually waste fuel.  Cats are a product of the 70's emissions mess.

Of course this it just what I've read on on the internet and heard from a couple real life mechanics. I'm no scientist.

[prmas]

Old Mechanic knows what he is talking about.

[RossLH]

FYI, I have read that modern cars do not need cats. The computer controlled electronic injection takes care of the fuel/air mixture. Catalytic converter actually waste fuel.  Cats are a product of the 70's emissions mess.

In a perfect world, cats would not be necessary. Fact of the matter is there is no good way to combust every last bit of fuel every time the engine fires. There will always be some left unburnt, and that's where the cats come into play. Unburnt and partially burnt gasoline results in emissions of nitrogen oxides (NOx), carbon monoxide (CO), and hydrocarbons (HC). Modern 3-way cats convert NOx into nitrogen gas and oxygen gas, CO into CO2, and HC into CO2+H20.

Perfect conditions are not possible. Catalytic converters make up for that.

[john]

FYI, I have read that modern cars do not need cats. The computer controlled electronic injection takes care of the fuel/air mixture. Catalytic converter actually waste fuel.  Cats are a product of the 70's emissions mess.

In a perfect world, cats would not be necessary. Fact of the matter is there is no good way to combust every last bit of fuel every time the engine fires. There will always be some left unburnt, and that's where the cats come into play. Unburnt and partially burnt gasoline results in emissions of nitrogen oxides (NOx), carbon monoxide (CO), and hydrocarbons (HC). Modern 3-way cats convert NOx into nitrogen gas and oxygen gas, CO into CO2, and HC into CO2+H20.

Perfect conditions are not possible. Catalytic converters make up for that.

Very true, but I wish cars didn't come with them because out here the people from south of the border cut them out of your truck with a hacksaw faster than you can say "what happened?"  They sell them for twenty bucks to the scrap yards (which know they are stolen), and YOU get to spend a few hundred for a new cat.

Personally, I have no issue with catalytic converters.  They seem to be made better these days, they don't plug as easily, and you can run a straight pipe off them and get a really nice exhaust note.

FYI, emissions testing of the zx6r with cat converter, and my z1000 without shows mine is cleaner running.  Go figure.

[The Buddha]

Here is a tip. Take it or leave it. Most modern cars have two 02 sensors. One before the cat and one after the cat. If your car is giving a check engine light or 420 code you will start burning trough sensors. Factory sensors will last longer but not as long as the original sensor. Aftermarket sensors are crap. Do this...put a spacer between the sensor flange and exhaust mount flange. This will get the sensor out of the direct path of the exhaust flow. The sensor is measuring the differences in O2/fuel as it passes through the cat. It will through a code if the readings the computer takes fluctuates to much. Removing it from the flow will keep the check engine light off. The object is to get the sensor (usually the one after the cat) out of the exhaust flow.

The sensor before the cat will read ups and downs in the fuel air mixture and the computer knows this. The one after the cat should be reading much less fluctuation because the cats job is to burn off the leftover fuel. If the sensor after the cat detects to much fuel your cat might be out of spec but not clogged.

FYI, I have read that modern cars do not need cats. The computer controlled electronic injection takes care of the fuel/air mixture. Catalytic converter actually waste fuel.  Cats are a product of the 70's emissions mess.

Of course this it just what I've read on on the internet and heard from a couple real life mechanics. I'm no scientist.

This car has 3. front cyl bank, rear cyl bank and after they join.
Dunno if that is before or after the cat.
The 2 on top I have swapped in the last few days and there is an OEM in both now.
I am going to find out which one is bad, and see if its not the one in the collector and see if I can swap it out.

Else I have no idea, maybe somehting is killing them in this car.

Cool.
Buddha.

[RossLH]

The only thing I could think of that would rapidly kill O2 sensors is a bad heater circuit. Those 4-wire sensors tend to die pretty quick if their heaters don't work properly, which I learned the hard way after burning through a couple wideband O2 sensors on my old car.

[The Buddha]

You probably are right. I seem to be losing one every day now.

Is that something in the car wiring harness ... and can the sensor work without the heater ... I know of 2 wire sensors that are a voltage only - can I use that ... and not heat it at all.

The heater is run by a relay isn't it - I guess I should find it.

Cool.
Buddha.

[RossLH]

The 2-wire sensors are narrowband sensors, the 4-wire sensors are wideband. It is possible that the ECU uses the 4-wire sensors as narrowband sensors, but I highly doubt it. Chances are the ECU depends on the accuracy of the wideband, replacing it with a narrowband sensor would only lead to more issues.

I don't know about your specific wiring harness, but I'd bet you can trace the heating circuits on all of the sensors back to a single relay.

[The Buddha]

OK  I found the bad sensor as per the diagnostic reader, and yesterday I swapped the front one to back. Lets see if it comes back on, and lets see if it still says front (like yesterday) or if it changes to rear - where I moved the bad sensor to. Maybe something in the car is making the sensor read a problem, and I am thinking its the sensor.

If the rear is bad now, its the sensor.
If the front is bad, its not the sensor.

Cool.
Buddha.

[Snake2715]

First www.rockauto.com is your best friend when it comes to parts. destroy any local place on price and brands.

the converter already shot from the first one?

I have also had bad experience with say a "standard" brand (literally the brand name) which is common on GM/Chevy in a ford... standard makes em for ford cars as aftermarket but they never did as well. I try to keep appropriate brands within the cats.. i.e. autolite plugs in Ford's, Bosch in Porsche, etc. I don't run OEM a lot, but I don't put autolites in GM or Chevy either.

Funny thing I have had a few cars where the O2 sensor is right below the oil filter..change the filter dump oil over it all.. one car like that foulded sensors a lot. the other never missed a beat.

[RossLH]

I try to keep appropriate brands within the cats.. i.e. autolite plugs in Ford's, Bosch in Porsche, etc. I don't run OEM a lot, but I don't put autolites in GM or Chevy either.

As far as 4-wire sensors go, I tend to stick with Bosch, no matter the car.

[john]

OK  I found the bad sensor as per the diagnostic reader, and yesterday I swapped the front one to back. Lets see if it comes back on, and lets see if it still says front (like yesterday) or if it changes to rear - where I moved the bad sensor to. Maybe something in the car is making the sensor read a problem, and I am thinking its the sensor.

If the rear is bad now, its the sensor.
If the front is bad, its not the sensor.

Cool.
Buddha.

Logical enough.  A good start to narrowing down the issue anyway.

[The Buddha]

Standard appears to be junk ... however the car now has original parts - pulled from other mitsu's from the junkyard.
Cool.
Buddha.