Oxygen Sensor Question

I am going to be replacing my entire exhaust system with a custom high-performance setup. One part that I always was unsure about is the O2 sensor. I know what it is, I know what it does (Wikipedia is very helpful). The only thing I can't seem to find out is if I can run without it? And if it helps at all, I am going with an exhaust system that does not have a catalytic converter.

I realize that the check engine light will come on, but I'm getting an OBDII cable to reset it. I am trying to get as much performance out of this exhaust as possible and I don't care about emissions or increased fuel-usage. The thing is, I do care about my engine. If the lack of an O2 sensor is guaranteed to harm my engine, I'll probably install one.

Also, in my stock setup it has two O2 sensors. One on the headers and a second one after the cat. conv. If I have only one O2 sensor (on the headers), will it still be the same? From all I've gathered, the second one is basically just to tell you if your cat. conv. is bad/going bad.

Thanks in advance for any help!

Your O2 sensor is what tells teh computer how to mix the fuel. it's absolutely necessary. Try to locate it in teh same place as stock on teh new exhaust, so it can measure teh exhuast properly. The after cat O2 sensor is, as you surmised, there to tell the computer whether the cat is working properly. it can be removed or made non-functional and it wont' affect how the car runs at all. BUT, as you guessed, it will set off the check engine light. You can reset it, but it will keep coming back on every 60 miles or so. A better idea is to use it, but instead of just putting an O2 senosr bung in the exhuast downstream and deal with it, you shoudl use a spark plug anti-foul device in the O2 sensor bung, drilled out to allow the O2 sensor to mount, maybe doubleing up on it. What this does is to take the rear O2 out of the exhaust stream so it reads as though the proper amount of work is being done by the no longer existing catalytic converter.

http://www.google.com/search?hl=en&rlz=1G1GGLQ_ENUS364&gs_sm=e&gs_upl=31l2406l0l3203l15l9l0l3l0l0l218l577l0.2.1l3 l0&q=o2%20anti%20fouler%20mod&spell=1&sa=X

these links show how that's done.

Out of curiosity, why not use a high flow catalytic converter in the exhaust? It can work liek a muffler/resonator and they are rather cheap from Magnaflow (I used a pair of Magnaflow high flow cats in my BMW and removed the mufflers for a high performance exhaust that is still clean)

Your O2 sensor is what tells teh computer how to mix the fuel. it's absolutely necessary. Try to locate it in teh same place as stock on teh new exhaust, so it can measure teh exhuast properly. The after cat O2 sensor is, as you surmised, there to tell the computer whether the cat is working properly. it can be removed or made non-functional and it wont' affect how the car runs at all. BUT, as you guessed, it will set off the check engine light. You can reset it, but it will keep coming back on every 60 miles or so. A better idea is to use it, but instead of just putting an O2 senosr bung in the exhuast downstream and deal with it, you shoudl use a spark plug anti-foul device in the O2 sensor bung, drilled out to allow the O2 sensor to mount, maybe doubleing up on it. What this does is to take the rear O2 out of the exhaust stream so it reads as though the proper amount of work is being done by the no longer existing catalytic converter.

http://www.google.com/search?hl=en&rlz=1G1GGLQ_ENUS364&gs_sm=e&gs_upl=31l2406l0l3203l15l9l0l3l0l0l218l577l0.2.1l3 l0&q=o2%20anti%20fouler%20mod&spell=1&sa=X

these links show how that's done.

I may try that trick for the second O2 sensor if I keep the first. However, I may go without any O2 sensors. I did some reading since my last post and I think I may have stumbled on a benefit of removing the O2 sensor(s). If anyone on here knows better, please let me know if what I'm about to say is complete bull. Here it goes:

When reading about OBDII tweaking software, I have heard that if you do tweak the ECU, it will basically reset itself with information gathered from the sensors. If the sensors are gone, the ECU can't change what you have already changed. I am going to go sensor-less on the custom air-intake that is soon-to-be-built.

Let me just say this: I hate sensors and computers in cars. I don't want the ECU making decisions for me. I want to make the decisions in my engine. It would be nice if things were manually, mechanically adjustable, but modern cars rely so much on computers. Traction/stability control? Hate it. Which is why I'm glad my car doesn't have it :biggrin:

Out of curiosity, why not use a high flow catalytic converter in the exhaust? It can work liek a muffler/resonator and they are rather cheap from Magnaflow (I used a pair of Magnaflow high flow cats in my BMW and removed the mufflers for a high performance exhaust that is still clean)

I want the exhaust to be as unrestricted as possible. The cat. conv. is simply there because the EPA decided to stick their noses into our own personal vehicles and try and 'help save the environment'. The catalytic converter just cuts down my performance. Plus, I live in KY and they are very lax on the emissions testing. However, if worst comes to worst and they decide to start checking again, I'll just slap that cat. conv. on and wait until their testing period is done and take it back off :lol2:

I may try that trick for the second O2 sensor if I keep the first. However, I may go without any O2 sensors. I did some reading since my last post and I think I may have stumbled on a benefit of removing the O2 sensor(s). If anyone on here knows better, please let me know if what I'm about to say is complete bull. Here it goes:

When reading about OBDII tweaking software, I have heard that if you do tweak the ECU, it will basically reset itself with information gathered from the sensors. If the sensors are gone, the ECU can't change what you have already changed. I am going to go sensor-less on the custom air-intake that is soon-to-be-built.

Let me just say this: I hate sensors and computers in cars. I don't want the ECU making decisions for me. I want to make the decisions in my engine. It would be nice if things were manually, mechanically adjustable, but modern cars rely so much on computers. Traction/stability control? Hate it. Which is why I'm glad my car doesn't have it :biggrin:

The computer is simply man made programming to make the fuel managemant as efficient as possible. it works VASTLY better thana carburator (which also makes all the decisions for you after you have set it, much like a fuel injection map) the difference is that the carburator doesn't adapt to changing conditions liek EFI does, so foregoing EFI's benefits seems a step backwards and counter productive, just to say you don't have tech on the car. Seriously. A good O2 setup with the computer monitoring it is vastly better a tthe job than tweaking the fuel map by hand for every change you encounter, and can give you more power AND more efficiency at the same time.



I want the exhaust to be as unrestricted as possible. The cat. conv. is simply there because the EPA decided to stick their noses into our own personal vehicles and try and 'help save the environment'. The catalytic converter just cuts down my performance. Plus, I live in KY and they are very lax on the emissions testing. However, if worst comes to worst and they decide to start checking again, I'll just slap that cat. conv. on and wait until their testing period is done and take it back off :lol2:

A good high flow catalyst will make the air cleaner AND give you as unrestricted exhaust as you can use. Is your car a turbo car? If it is, I can see trying to get as big an exhaust as possible, but if it isn't you NEED a bit of restriction to get a proper scavanging effect. And a big exhaust with a big cat can give you clean air, unrestricted flow AND reduce the tone like having a resonator and muffler. I removed the mufflers entirely on my daily driver because the high flow cats do a good enough job, while making the exhaust flow MUCH better than stock.

Seriously these days there's little reason to go back to carbs and non catalyst equipped systems to get the power you want. And just saying "I want my car to run dirty and innefficiently" isn't really a good enough reason. :wink:

I may try that trick for the second O2 sensor if I keep the first. However, I may go without any O2 sensors. I did some reading since my last post and I think I may have stumbled on a benefit of removing the O2 sensor(s). If anyone on here knows better, please let me know if what I'm about to say is complete bull. Here it goes:

When reading about OBDII tweaking software, I have heard that if you do tweak the ECU, it will basically reset itself with information gathered from the sensors. If the sensors are gone, the ECU can't change what you have already changed. I am going to go sensor-less on the custom air-intake that is soon-to-be-built.

Let me just say this: I hate sensors and computers in cars. I don't want the ECU making decisions for me. I want to make the decisions in my engine. It would be nice if things were manually, mechanically adjustable, but modern cars rely so much on computers. Traction/stability control? Hate it. Which is why I'm glad my car doesn't have it :biggrin:



I want the exhaust to be as unrestricted as possible. The cat. conv. is simply there because the EPA decided to stick their noses into our own personal vehicles and try and 'help save the environment'. The catalytic converter just cuts down my performance. Plus, I live in KY and they are very lax on the emissions testing. However, if worst comes to worst and they decide to start checking again, I'll just slap that cat. conv. on and wait until their testing period is done and take it back off :lol2:



If you hate modern computer controlled engine management systems, and the massive benefits they offer in terms of performance, reliability and efficiency, then sell your car and go buy something from the 60s or 70s.


Removing the O2 sensors will not do good things and the car will not very well.
What ever you read about the system staying closed loop will only apply to some engines, and staying closed loop is not for them. It's intended to get the car home should something fail.
Driving it long term could lead to a wrecked engine, as it will run to rich, or to lean both of which can be fatal in different ways.

The O2 sensor is there to tell the computer how rich or lean the fuel mix is, and adjust it accordingly, it's fundamental to the engine running properly.

I certainly prefer things to be simpler as well, but I do like the ECU's capability of helping to diagnose problems.

Not that I'm condoning this, but if you're gonna delete the O2 sensors then you might as well delete the cats, too. This for the simple fact that running an OBD-controlled car without sensors will cause it to run in open-loop mode, which is a richer fuel delivery. The excess fuel gets into the cats and overheats them because it is trying to eliminate them from the exhaust. This causes them to melt inside and become plugged, ruining performance and destroying a pair of expensive cats.

You can run the upstream sensors but delete the cats and downstream sensor(s). An ECU reprogram or wiring trickery would be needed to counter the missing sensor, but you'd get reasonably efficient performance and free-flow exhaust.