My exhaust is slowly starting to rust away and while I'm at it I might as well replace it...but it has 2 O2 sensors! One before and after the cat. I don't want the catalyic converter and I don't want it to throw codes. Is there some way I can bypass this without throwing a CEL?

Thanks, Trevor

 

You might get lucky and it not throw any codes depending on how bad the actual emissions is on the engine. But in case you do:

 

What the heck is that?

 

don't laugh it works. The idea behind it is that it keeps the 02 sensor hooked like it should but keeps the probe out of the exhaust flow. So if you have enough junk in the exhaust to trigger the cat efficiency CEL it goes right by the sensor.

I did this exact same thing on the Elantra that I had a gutted cat on. Beats paying $45-60 on an 02 simulator. Casper Electronics used to sell one for like $15 years ago but were sued by the EPA and were forced to stop selling theirs.

 

I'm guessing that is a set-up to fool the downstream O2 sensor. When you eliminate or punch out the cat, too much unburned exhuast gases will be registered by the 2nd O2 sensor. So by pulling the sensor out of the direct stream of exhaust gases you might be able to fool the ECU.

 

^^^^ yup, exactly, and to the untrained emissions guy it's easily passed off all they look for is the 02 sensor in place.

 

I'm no EE by any means, but could this also be done with an inline resistor in the wiring loom?

 

not that simple wanna make you own, this is what it would look like:

http://www.mkiv.com/techarticles/oxy...sor_simulator/

 

I wouldn't mind adding a resistor. Just need someone to teach me

I dont have emissions around here. I have a 2.25" flowmaster i've been wanting to put on but I don't want to loosen any rusty bolts because I know they will snap.

 

I believe the MKIV site is proposing a simulator for the FRONT O2 Sensor. It fakes up the 0.1 to 0.9 volt signal of a working O2 sensor. But since it would have nothing to do with the actual exhaust stream, it would just be forcing the mixture back and forth randomly. So it would only be useful if you had a completely different way to set the mixture -- essentially replace the ECM (and if you did that, it wouldn't be throwing any codes any way ...)

I think 91Toyota just wants to replace the back O2 sensor, which he would need to do if he has no cat (if the cat is working, the back sensor should not see the switching of the O2 level that the front sensor sees -- so it throws a code that the cat is failing). A resistor "shouldn't" work, because an O2 sensor is a voltage source, not a resistance. (replacing it with a 0.2v voltage source should work, but it's certainly more work than a resistor). But I don't know the internals of the ECM circuit, it is possible a resistance could fool it. But I have no idea what resistance to start with. Perhaps someone has done the experimenting and figured out something that would work, but I haven't seen it.

 

"If you install the aftermarket downpipe with no cat (which as we all know is purely for off-road applications) the ECU will detect this and indicate the error (MIL). The ECU is quite lazy at detection, and detects this condition approximately during second long trip. You can reset the ECU to clear the error code, but it's very inconvenient, as you don't really know if the error was because of oxygen sensor or some important thing is wrong and needs to be taken care of ASAP. It's also quite annoying."

nope they are talking about installing a test pipe in place of the cat.

notice how the out goes to pin 47 " OX2 sub heated o2 sensor. Ox1 (pin 48) is the main heated o2 sensor.