MJH78

Ok the 4 O2's I removed and replugged into my Prochamber..there were two (one on each side) before the cats and two after the cats. Am I correct that these 4 sensors are for emissions only..to tell the computer if the cats are working effectively? If so, where are the sensors that actually deal with engine function...reading whether or not the engine is running rich or lean and adjusting accordingly?? I had always thought an OR pipe would have ZERO effect on engine function, am I correct? I've read a lot of crap (not on MF) of people saying removing cats can cause fires, your engine will not run right, it will get so hot under the car the wires will melt, on and on..

zinc02gt281

So far what youve heard for the most part is bull****...

The only thing an offroad mid pipe will cause you to do is run a little rich. Basically around .5 of where it should be on the AF ratio...

MILs will cancel out the SES light, but unless you get a tune, ti will always be slightly rich.

O2 sensors are there to make sure the cats are running efficently. the 2 near the headers are to basically set a base line for what the computer expects. the ones after the cats is to compare the frequencies of the orimaries and the secondaries to judge weather or not it has passed through a working catalytic converter.

No, your car will not catch fire, your engine will still run right, and no it will not melt wires... unless your O2 sensors are directly touching your exhaust components. Even then I dont think itd melt them completly

Eagle2000GT

I was told that the front two are used by the computer to adjust the A/F mixture. The back two are for emissions and that mil-eliminators are for the rear 02 sensors. That's why you run rich when the front onesare not present. The computer is trying to protect the motor. When I had my headers installed we used O2 extenders to keep the front two working. We turned off the rear sensors.

zinc02gt281

YOur still going to run a little rich because the unburnt wouldve been burnt up by the cats and now its not...

Your correct eagle.

I tried to make it simle, but i may have come across as a little awkward. basically what I was trying to say is that the front O2s are straight exhaust fumes. They havent had any means of emissions unless you want to get into the EGR valve...

Basically it uses a constant exhaust gas and compares it to the end prduct after the cats by reading the rear O2s. Thats why MILs are required on the rears if you dont get a tune to keep the SES light from popping up

MJH78

So what's coming out the tailpipe is too rich because of having no cats, but the AF ratio in the combustion chambers woudl not be affected? Hope that makes sense..

I guess what I mean is...the O2 sensors that effect the AF ratio in the combustion chamber are the ones PRIOR to the cats, right? so even if you remove the cats, this would not have any effect on the readings the front O2 sensors are getting becase they are before the cats. am I right? So I guess I am a little confused why an OR pipe would cause you to run rich, unless you just mean rich coming out of the tailpipe. am I on track?

blstoff

the front 02 sensors trim the fuel in closed loop so it runs 14.64:1 A/F ratio . it will not run rich w/aftermarket mid-pipe .

Eagle2000GT

I may have read the OP wrong but I think he took out all 4 O2 sensors.

Nitti00GT

First off you need your front O2s. They are used to help calulate the fuel needed to properly maintain an a/f ratio as close to 14.7:1 as possible. Without the front O2s your car will run like crap and dump fuel. Removing the cats will not cause a fire but it could throw off your front O2s ability to read the a/f ratio because the exhaust gases will be moving faster past the O2s. I had that problem with my car cause of the longtubes and the o/r H. The rear O2s only job is to make sure the cats are working properly by comparing the readings from the front O2s with the rear O2s.

MJH78

Yeah I took them out of the stock H-pipe and "plugged" them back into my prochamber after I installed it..

cliffyk

OK, here's the straight dope...[/align][/align]The front sensors providetheonly feedbacksignal the PCM receivesto perform fueling calculations in closed-loop mode; they are not "helpers", they are it.[/align][/align]But, becausea narrowband sensor cannot indicaterich or lean with any degree of accuracy, and other than within a very narrow band of its output, it cannot accurately indicate a stoichiometric mix (14.7:1 for air/gasoline); that's the narrowband part. [/align][/align]Also, often (like under light and steady loads) the PCM will keep the mix leaner than 14.7:1 for improved fuel economy; sometimes as lean as 16.0:1 or leaner.[/align][/align]So in closed-loop mode, to keep the AFR where it wants is to be, the PCM monitors the O2 sensor output andvaries the injector cycle so as to keep the average voltage of the sensor's AC output indicating the AFR it wants.[/align][/align]Installed and properly operational front O2 sensors are 100% required for the engine to operate properly...[/align][/align]The rear sensors also monitor the exhaust gas oxygen content, however only for the purpose of monitoring the efficiency of the cats. [/align][/align]The rear O2 sensors have nothing to do with engine control.[/align][/align]The catalytic converters store quite a bit of oxygen in their process and this causes the rear O2 sensor output to be quite a bit less than the front sensor output, and also causes it to switch at a lower frequency (more about this later). [/align][/align]MIL eliminators are simplesingle pole RC (Resistor/Capacitor)filters that attenuate (reduce) the rear sensor output (which without cats is the same as the front sensor's output), and also introduce some phase shift into the filtered signal. For most ECUs this is enough to trick the computer into thinking that the cats are there and doing their job.[/align][/align]However, some modern ECUs also check the frequency of the rear signal as compared to the front and expect it to be slower. If it is not the cat monitoring test will fail. The new-edge Mustangs do not seem to perform this test and are content toaccept the lower amplitude signal as proof that the cats are installed and working.[/align][/align]Obviously for this to work the rear sensors must be installed and fully functional or their will be no signal to filter.[/align][/align]Recap:[/align][/align]
[ol][*]The front sensors are essential to proper engine control;[*]The rear sensors are ONLY used to monitor the cats;[/ol]
[/align]In the last, there is no reason why an o/r pipe should make an engine run rich. I'm not saying it doesn't to those who have experienced it, however there in nothing about the EEC-V PCMs engine control functions that should care whether the cats are there or not. No cats will make it stink like it's running a bit rich...[/align][/align]================================[/align]If you are not sufficiently bored yet you can read more about how narrowband sensors work here.[/align]