x pipe w/o mil eliminators

If your running with no cats at all your going to need the MIL kit. If you just put your 02 sensors back in the computer is going to read emissions comming out of the engine and after what used to be the cat. When it sees that there is no difference in emissions after the cat it will throw a cat inefficent code which may cause the computer to lean out the engine which will not allow the engine to run right. The MIL kit is only around 50-60 bucks its a good buy.

Very incorrect.

The rear o2's ONLY tell the computer if the cat is working or not. They have ZERO effect on the a/f ratio's. Obviously if you run then w/o cats your computer will think the cats are not working and trip the cel code. Performance and fuel mileage will NOT be effected.

PS.. Do a search, if you can solder, you can make a set for 5 bucks. I've made them multiple times.

Is it true you can do the same thing that the MIL eliminators do with a programmer? i.e. turn off the check engine light? Seems like I've heard that somewhere before but I can't find any confirmation right now.

I ask b/c I have both an SCT programmer and an offroad h-pipe on the way, and was wondering if it was even worth the trouble to buy/make MIL eliminators.

-Will

I ran mine for a bit with no issues... I do have the plug in MIL eliminators that I picked up for $25 used.

You have to turn off the rear sensors and heaters to keep the code away.

The computer uses the oxygen sensor input to regulate the fuel mixture, which is referred to as the fuel "feedback control loop." The computer takes its cues from the O2 sensor and responds by changing the fuel mixture. This produces a corresponding change in the O2 sensor reading. This is referred to as "closed loop" operation because the computer is using the O2 sensor's input to regulate the fuel mixture. The result is a constant flip-flop back and forth from rich to lean which allows the catalytic converter to operate at peak efficiency while keeping the average overall fuel mixture in proper balance to minimize emissions. It is a complicated setup but it works.

stangman11 said:

The computer uses the oxygen sensor input to regulate the fuel mixture, which is referred to as the fuel "feedback control loop." The computer takes its cues from the O2 sensor and responds by changing the fuel mixture. This produces a corresponding change in the O2 sensor reading. This is referred to as "closed loop" operation because the computer is using the O2 sensor's input to regulate the fuel mixture. The result is a constant flip-flop back and forth from rich to lean which allows the catalytic converter to operate at peak efficiency while keeping the average overall fuel mixture in proper balance to minimize emissions. It is a complicated setup but it works.

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That is correct for the FRONT set of o2's. MILS are used in the rear set which ONLY measures the output after the cat to see if the cats are working or not. They have zero control over a/f. The fronts do ALL of that.

squeak93 said:

That is correct for the FRONT set of o2's. MILS are used in the rear set which ONLY measures the output after the cat to see if the cats are working or not. They have zero control over a/f. The fronts do ALL of that.

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the rears ONLY see if the cats are working properly. they have NOTHING to do with how the car runs. i used my Xcal2 to disable the rear o2's EGR and evap system codes

stangman11 said:

The computer uses the oxygen sensor input to regulate the fuel mixture, which is referred to as the fuel "feedback control loop." The computer takes its cues from the O2 sensor and responds by changing the fuel mixture. This produces a corresponding change in the O2 sensor reading. This is referred to as "closed loop" operation because the computer is using the O2 sensor's input to regulate the fuel mixture. The result is a constant flip-flop back and forth from rich to lean which allows the catalytic converter to operate at peak efficiency while keeping the average overall fuel mixture in proper balance to minimize emissions. It is a complicated setup but it works.

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Way to try and google yourself a correct answer. BTW You're dead wrong.

wow stangman thats a lot of typing when the answer you gave only sounds rite when you say it fast, the rear o2 sensors measure the heat difference from the front 2 to the rear 2. if the differenceist to high the computer sends a code. if the difference is to low or the same the computer sends a code. the mil elims, are simply a signal reducer, the signal i think is only a .5 volts of difference. i think, if im wrong please some one correct me.

Funny,!

think you ill be here all night, good evening trombonedemon.

the rear o2 sensors have nothing to do with you engines performance. think of it as a tool to measure emmisions. the front two sensors are the ones you should worry about. they will affect the performance of the stang. the rear o2 sensors just tell your car if your cats are running well or not so when you get an inspection you can pass the emissions test. Mils are really just a set of resistors spliced into the 02 sensor harness to trick the computer into thinking that you are running clean emissions. i have my rear o2 sensors tunrned off in my tune so i have no need for mils. I have 2 sets though that i have to sell since they are not being used.

Wow my bad guys I dont know where the hell my head was yesterday you guys are absolutely right about the rear o2 sensors. Sorry for all the bs responses.

fronts will not be affected, but when i did mine they were hard as hell to plug in without the extension kit, but its doable. and im pretty sure you could just unplug the battery and the CEL will go away, but easiest way is to just get a tuner and turn off the rear o2s. but be sure to drive it for about 5 days or so after unplugging the battery before getting it inspected or you will not pass OBDII test.

fast97gt said:

wow stangman thats a lot of typing when the answer you gave only sounds rite when you say it fast

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Actually, it wasn't. Read the "LOOPS" section here:

WHAT THE HOME MECHANIC NEEDS TO KNOW ABOUT O2 SENSORS

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the rear o2 sensors measure the heat difference from the front 2 to the rear 2. if the differenceist to high the computer sends a code. if the difference is to low or the same the computer sends a code. the mil elims, are simply a signal reducer, the signal i think is only a .5 volts of difference. i think, if im wrong please some one correct me.

Click to expand...

As has been noted previously, the rear O2 sensors simply measure how well the catalytic converters are doing their job. The front O2 sensors are used by the PCM as feedback sensors during closed loop fuel operation. When the PCM makes a change to the injector pulse width, the front O2 sensors reflect that change as a change in voltage indicating a richer (>450mV) or leaner (<450mV) mixture. The PCM adjusts its fuel delivery such that the O2 sensor voltage swings repeatedly back and forth across this 450mV threshold. The average mixture composition when this is happening is 14.7:1. So front O2 sensors are supposed to show voltages moving roughly equally between 0V (lean) and 1V (rich) as part of the loop control.

Rear O2 sensors should not show such wide variations if the cats are doing their job. The cats change in exhaust gas chemistry, dealing with things like unburned hydrocarbons (raw fuel), oxides of nitrogen and so on, converting them to carbon monoxide, carbon dioxide, water and other less harmful compounds. Thus, the exhaust downstream of the cats should be of fairly consistent composition during closed loop. In other words, the comparatively wild, but normal, +/- (wrt 450mV) swings of the front O2 sensors are damped heavily by the cats resulting in a much more slowly moving signal with much less amplitude. Of course, if the cats are absent, as with an O/R pipe, the rear O2 sensors see essentially the same exhaust gas chemistry as the fronts, just a bit cooler as the gas has traveled through an additional foot or two of pipe. In that case, the rear O2s will show very similar signals to the fronts and the PCM will know that something is up with the cats.

MILs or "elims" are nothing more than electrical low-pass filters. They are typically a very simple, single-pole RC (resistor-capacitor) filter consisting of perhaps a 1M series resistor in the O2 sensor signal line and a 1uF parallel capacitor between the signal line and the ground return line. The resistor and capacitor serve to "dampen" the voltage swings coming off the rear O2 sensor so they appear very similar to what the signal would look like if a cat was present. The MILs filter out the higher-frequency switching and reduce the amplitude of the voltage swing. This filtering is enough to fool the PCM into thinking cats are present.