02 Sensor Questions

[Sbaileyls1ta]

Not very familiar with 02 sensors, and have a few questions. I have a 99 ta with long tube headers, y pipe, and magnaflow. At the end of last year I was having a problem with an 02 sensor, and a buddy of mine told me to just unplug them all for the time being and it would just go into like a dummy mode. It ran fine until I stored it. My questions are, how bad is/could it be to run with no 02s. Also with my exhaust i though i read somewhere that only the fronts are needed? and lastly I only remember seeing three. The front two were hooked up, to driver side rear was cut off right at the exhaust?? and i don't remember if the pass rear was connected or not. Just wondering what i should do. I'm have a bit of money now from taxes and such so I want to get the taken care of, but still would like to get out of it pretty cheap. Also very occasionally the car will kind of bog down until I really get on the gas and then it goes into rocket mode. The line by my pvc valve is also collapsed (assuming possible vacuum leak?) so I'm replacing that to since its only like 2.99. Any help here will be greatly appreciated!

[BP_Z28]

Ditch the rears..plug the hole.keep the fronts

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[Sbaileyls1ta]

Ditch the rears..plug the hole.keep the fronts

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So I assume by "ditch the rears" this is why the rear was cut off? So if would just be an open hole...

[Sbaileyls1ta]

Also could that pcv valve vacuum leak have maybe caused the problems with the o2s?

[Boost Addict]

The rears just monitor your catalytic converter efficiency. The fronts are what reads your air/fuel ratio. I wouldn't unplug the fronts. No reason to.

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[meissen]

Also could that pcv valve vacuum leak have maybe caused the problems with the o2s?

An intake vacuum leak or an exhaust leak that's upstream of the O2 sensor would definitely cause you an issue with your o2s. Your MAF sensor is reading how much air is coming into the engine which will end up in the combustion chamber - the MAF sensor's reading is what determines how much fuel to use for combustion. If you have any un-metered air coming into the combustion chamber (IE: a vacuum leak) then you're going to have too much oxygen and not enough fuel. Depending on how bad the vacuum leak is and if your fuel pressure regulator is vacuum controlled like on the LT1s, then your fuel pressure regulator will automatically command more fuel because of the loss in vacuum. Otherwise, your O2 sensor will see you're running lean and will tell the PCM to compensate. Depending on how bad the vacuum leak is, your PCM could compensate enough by adding the right amount of fuel.

In the case of an exhaust leak, you have air being sucked into the exhaust which will make your O2 say "Wait a minute - there's too much oxygen in the exhaust. PCM - add more fuel!" even though your air/fuel ratio is actually OK, it's that air being sucked into the exhaust that's throwing the reading off. In that case, because of the exhaust leak you'd be running rich.

That said -- are you sure the PCV Valve has a vacuum leak? One way to check for vacuum leaks would be to buy carb cleaner and spray around areas you think might have a vacuum leak. If your RPM surges, you have a vacuum leak. The carb cleaner is getting sucked in through the vacuum leak and adding more fuel to the mixture, increasing your RPMs. If your RPM stays unchanged you do not.

Also on the topic of O2s -- when it comes to unplugging all the O2s your friend was right, it will make the car go into an "Open Loop" mode which means the PCM is not using (or in this case - not able to use since the O2s are unplugged) the O2 sensor readings, and thus the PCM is not getting "feedback" (or "closing the loop") on whether the air/fuel mixture is right. When your O2 readings are being used, you go into "closed loop" because the PCM is getting the "feedback" from the O2 sensors saying "Yep - the mixture is just right!" or will be telling the PCM to adjust the fuel amount. Our cars start in Open Loop when the car and o2 sensors are cold. Once the O2 sensors warm up and are ready, then the car goes into closed loop automatically. In your case with the o2s unplugged, your car would just stay in open loop all the time. Likewise, some tuners will force a car to stay into open loop all the time.

Like Ricky said - front O2s are for air/fuel ratio for the closed loop / feedback, rear o2s measure the catalytic converter and can removed and where the O2s go should be plugged.



Sorry - that was kind of long winded ...

[Sbaileyls1ta]

Yeah that was, but was worth it. And basically the roughly 2-3 inches of tubing from the end of the pcv valve to the intake had a literal hole in it. I fixed that, and it ran fine. Then i decided to plug the 02s back in for the fronts, and got about 1/4 mile and it starting bogging down and had no acceleration. I assume that just means replace the o2 sensors for the fronts. Should I try one at a time or is it best to replace both at once?

[Boost Addict]

Do you have a diagnostic tool? If so then you can determine if they are switching correctly or if 1 or both is bad

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[Sbaileyls1ta]

and that would basically be saying bank 1 or 2. and whatever one it trips is the bad one or both.. Ill swing up to work with it and try it out. Thanks

[Boost Addict]

It wont always throw a code, you have to look at sensor data and see that both sensors are switch from about 100-900 mv. If one is stuck at a certain value you know you have a problem somewhere.

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[farmington]

O2 sensors do wear out. They're not cheap but if your car has over 100k miles, it wouldn't hurt to replace them.

[nascarnate326]

Id go on rock auto and get your self two new front O2 sensors. Avoid Bosch, many issues with those.

[BP_Z28]

Been rocking Bosch for 3 years..not one problem

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[nascarnate326]

On tech they have horrible reviews. Idk bunch about o2 sensors. Mine are delco.

[BP_Z28]

Tech has just as many good reviews, as they do bad..on practically everything in the LT,LS world ... Like all things, its always a hit or miss