I am trying to get buy my shot rear o2 sensor and not have the CEL codes for the rear oxygen sensor. I had an idea to connect the output of the front o2 sensor to the rear o2 sensor input on the ECU. Would this fool the ECU into thinking the rear is actually there and functioning properly? Or by doing that, is it going to make it think that the cat isn't there and spit out a code anyways?

Originally posted by rs-pssst
Or by doing that, is it going to make it think that the cat isn't there and spit out a code anyways?

Exactly.

maybe resistor mod the wires for the second o2 while it's hooked up to the front o2 maybe :shrug It may cause the car to think it's lean if you do that, but I really don't know.

yea, i think i'm gonna just try to see what happens. my car is running way to rich (10.0afr) and i think its cause of the rear o2 being shot. does anyone have any voltages logged for the rear o2 sensor?

Originally posted by rs-pssst
yea, i think i'm gonna just try to see what happens. my car is running way to rich (10.0afr) and i think its cause of the rear o2 being shot. does anyone have any voltages logged for the rear o2 sensor?

the rear o2 doesnt have any authority on pulsewidth ?

I thought it was discussed that if there is a check engine code displayed for the rear o2 sensor, that the computer will go into a "safe mode" and run rich or mess with timing?

it was discussed that a nonexistant/faulty rear o2 sensor will pull timing, but not have any bearing on your a/f ratio nor will it cause the computer to go into "limp" mode. if you dont want the cel, do the resistor mod. and if your running a turbo like your name suggests, how about tuning with your fuel system...thats why your running rich

causing the computer to pull timing is a problem -is it solved with the resistor mod? I am runnng turbo (18 psi daily driver) which is why i am worried about timing.

Originally posted by rs-pssst
(18 psi daily driver) which is why i am worried about timing.

cough* megasquirt cough*

Originally posted by 96eclipse2nr
it was discussed that a nonexistant/faulty rear o2 sensor will pull timing, but not have any bearing on your a/f ratio nor will it cause the computer to go into "limp" mode.

Where was this discussed? I am unable to find any data backing that. In my professional auto service experience, OBDII systems use the rear O2 input only for checking the catalyst.

Doing the resistor mod on the rear oxygen sensor, if done correctly, is not installing a resistor by itself. There is a capacitor in there as well. If watching the signal from an oxygen sensor there is a fluctuating signal as the computer continually pulls and adds fuel. The computer compares the fluctuating signal of the rear to the front. If they are identical then it knows the catalyst is not doing its job. With the catalyst performing as it should, the rear signal lags behind the front as the chemical reactions take place in the honeycomb inside the catalyst. Replacing the rear sensor with a resistor and capacitor creates a false fluctuating signal as the capacitor charges and discharges.

http://zero-signal.org/o2/O2bypass.html.htm

Originally posted by CODE4

Originally posted by 96eclipse2nr it was discussed that a nonexistant/faulty rear o2 sensor will pull timing, but not have any bearing on your a/f ratio nor will it cause the computer to go into "limp" mode.

Where was this discussed? I am unable to find any data backing that. In my professional auto service experience, OBDII systems use the rear O2 input only for checking the catalyst. Doing the resistor mod on the rear oxygen sensor, if done correctly, is not installing a resistor by itself. There is a capacitor in there as well. If watching the signal from an oxygen sensor there is a fluctuating signal as the computer continually pulls and adds fuel. The computer compares the fluctuating signal of the rear to the front. If they are identical then it knows the catalyst is not doing its job. With the catalyst performing as it should, the rear signal lags behind the front as the chemical reactions take place in the honeycomb inside the catalyst. Replacing the rear sensor with a resistor and capacitor creates a false fluctuating signal as the capacitor charges and discharges. http://zero-signal.org/o2/O2bypass.html.htm

http://forums.2gnt.com/dcboard.php?az=show_topic&forum=8&topic_id=81632&mesg_id=81632&listing_type=search

Originally posted by Collentethe rear 02 will do something when it sences the cat has taken a shit. It will pull timing, This has been dyno proven by hrc. But it wont really hurt fuel performance. That is all taken care of by the upstream 02.

Originally posted by rs-pssst
I am trying to get buy my shot rear o2 sensor and not have the CEL codes for the rear oxygen sensor. I had an idea to connect the output of the front o2 sensor to the rear o2 sensor input on the ECU. Would this fool the ECU into thinking the rear is actually there and functioning properly? Or by doing that, is it going to make it think that the cat isn't there and spit out a code anyways?

no, that would tell it exactly what its throwing a cel for,

in our cars, the downstream o2 trips a cel if the rear o2 is >.7x the front (MTX) or >.9x the front (ATX)

I had an interesting discussion at the Shootout with Bill and a bunch of other people about just this. The rear oxygen sensor DOES have an effect on peformance. It's there mainly to test the efficiency of the catalytic converter, but we all came to the conclusion that the ECU probably treats an oxygen sensor failure as a global error, regardless of which oxygen sensor is stuck putting out one voltage level.

The rear sensor's voltage should always be lower than the front one. This means the catalytic converter is working. The ECU will also check to make sure that both sensors are changing value, and that they are not stuck at one voltage. Therefore, if the rear oxygen sensor is stuck at one value (you have an exhaust cutout before the sensor or it's broken or disconnected) the ECU will treat it as if the front oxygen sensor has failed - it will fall back an open loop fuel map and will retard the timing.

I was a little drunk when we had that conversation at the shootout. Anyone care to elaborate?

Originally posted by ner947
I was a little drunk when we had that conversation at the shootout. Anyone care to elaborate?

I was too, but that's the gist of it. An O2 failure is an O2 failure, regardless of front or rear, and both will cause the same problems.. Open loop, pulled timing, loss of power and performance.

Y'all might get a kick out of this, but i figured out why my car never threw a no-cat CEL... i pulled the rear O2 out, and it was a solid cone of carbon... Nice.

So if the rear o2 is supposed to be reading lower voltages than the front and fluctuating... then couldn't the ouput of the front o2 sensor be hooked into the input of the rear o2 but with a resistor in between to lower the voltage?

Originally posted by DarkOne

Originally posted by ner947 I was a little drunk when we had that conversation at the shootout. Anyone care to elaborate?

I was too, but that's the gist of it. An O2 failure is an O2 failure, regardless of front or rear, and both will cause the same problems.. Open loop, pulled timing, loss of power and performance. Y'all might get a kick out of this, but i figured out why my car never threw a no-cat CEL... i pulled the rear O2 out, and it was a solid cone of carbon... Nice.

If you're not getting a CEL will it still pull timing?

casper electronics makes an o2 simulator, $40 bucks or so and problem solved.
The resistor trick usually works on most vehicals though, but the capser device works without a problem

with that o2 sensor link that was given it talks about using a 12 ohm resistor in between the heater wire and another wire. is this needed? couldnt the heater wire just be cut and taped off?? the only necessary thing should be the capacitor and the resistor between the power and signal wire right? that should fool the ecu? the grnd and heater can just be left cut off right?

NO. The ECU checks the heater circuit too.

ok well is that link color specific to our cars or is it general ? cause my o2 wires are not that color. i got a black . two white and a grey

Originally posted by DarkOne

Originally posted by ner947 I was a little drunk when we had that conversation at the shootout. Anyone care to elaborate?

I was too, but that's the gist of it. An O2 failure is an O2 failure, regardless of front or rear, and both will cause the same problems.. Open loop, pulled timing, loss of power and performance. Y'all might get a kick out of this, but i figured out why my car never threw a no-cat CEL... i pulled the rear O2 out, and it was a solid cone of carbon... Nice.

I have a rear o2 slow response code (the rear o2 sensor isn't hooked up at all), and it is not in open loop. The timing is not retarded at all either I don't think. So is this just a myth then? I'm about to go to radioshack to make a simulator just to get rid of the cell though. BTW, wouldn't it be a good thing for us turbo guys to retard the timing and stay in open loop because of the part throttle boosting problems?

Originally posted by ner947
I had an interesting discussion at the Shootout with Bill and a bunch of other people about just this. The rear oxygen sensor DOES have an effect on peformance. It's there mainly to test the efficiency of the catalytic converter, but we all came to the conclusion that the ECU probably treats an oxygen sensor failure as a global error, regardless of which oxygen sensor is stuck putting out one voltage level. The rear sensor's voltage should always be lower than the front one. This means the catalytic converter is working. The ECU will also check to make sure that both sensors are changing value, and that they are not stuck at one voltage. Therefore, if the rear oxygen sensor is stuck at one value (you have an exhaust cutout before the sensor or it's broken or disconnected) the ECU will treat it as if the front oxygen sensor has failed - it will fall back an open loop fuel map and will retard the timing. I was a little drunk when we had that conversation at the shootout. Anyone care to elaborate?

so the solution to this is...

It appears to me that the resistor mod should still work so long as the resistor is sufficient. A resistor won't stop it from fluctuating will it? I was discussing it with one of my buddies and we were thinking the signal wire to a t-off, a 20% resistor to the harness and an 80% resistor to ground (grnd-80%-signal-20%-harness) it makes more sense on paper. Anyways, if you get what Im saying, tell me if Im right or wrong please.

doesn't the ecu read the voltage drop across the oxygen sensor? and the resistance of the sensor changes with the oxygen content? if so then i don't see how using just a resistor would possible give a fluctuating signal. the resistance and current are being held constant so why would the voltage drop change?

V=I*R

sorry if i'm way off on my understanding of how an 02 sensor works...

If the ECU needs to see a fluctuating signal then it makes a lot of sense to use the setup with the capacitor. Using just a resistor will not give you a changing voltage. I'm not sure if using just a resistor works on our cars or not, but if you're doing the mod, would it really be so hard to solder in a capacitor at the same time? :P

Originally posted by MCubed45
... If the ECU needs to see a fluctuating signal then it makes a lot of sense to use the setup with the capacitor. Using just a resistor will not give you a changing voltage. I'm not sure if using just a resistor works on our cars or not, but if you're doing the mod, would it really be so hard to solder in a capacitor at the same time? :P

My point is that a resistor won't change the fluctuation at all, it will still fluctuate. All the resistor does is drop the voltage a little. You want to duplicate what the Cat. does right? Well from an electrical standpoint, what does it do? It provides resistance, it lowers the amount of hydrocarbons (or whatever the O2 sensor see's) and provides more resistance. Am I way off here?

Sure. Try a simple voltage divider. Just be careful of what size resistors you pick. Too low and it will pull too much current from the front oxygen sensor. Too high and there won't be enough there to drive the input of the ECU.

I'd start off with...

Front O2 EGO -> 5k? resistor -> rear sensor wire that goes to the ECU -> 5k? resistor to ground

Give that a shot. It will flow about .1 milliamps, tops, which is nothing. I mean, you're not gonna break anything. If you ground the oxygen sensor, the worst thing that can happen is that you will need a new one. If you short an ECU input to something, I doubt that would do much of anything either. Those inputs should be high impedence.

I got parts coming in today for my O2 sensor eliminator. Using high watt wirewound resistors for the heating element (about 30 watt capability to be safe) and a resistor and cap. for signal circuit. I am putting it in an enclosure as well for heatsinking. I will take a few pics and let you guys know how it works.

just buy a new rear o2 sensor and stop fucking around.
no matter what you do with resistors some cars will still have the code come right back.

Originally posted by mcgyvr
just buy a new rear o2 sensor and stop fucking around. no matter what you do with resistors some cars will still have the code come right back.

yeah, but to those with test pipes and gutted cats, you cant just solve the CEL by replacing the sensor...if you wanna continue to run that setup, you gotta eleminate it. true, if you have a fully functioning catalyist system...and ur light is on...yeah, stop messin around and buy another one. but thats not a solution for people who actually CAUSE this problem by bypassing emissions equip.

yeah but your killing my air/trees :)
seriously for the 1hp and the raspy sound your gaining its not worth it. IMO
keep emissions intact, just up the boost }(

Seriously the casper o2 simulator is the way to go, solves the problem right away.

Originally posted by 96eclipse2nr

Originally posted by mcgyvr just buy a new rear o2 sensor and stop fucking around. no matter what you do with resistors some cars will still have the code come right back.

yeah, but to those with test pipes and gutted cats, you cant just solve the CEL by replacing the sensor...if you wanna continue to run that setup, you gotta eleminate it. true, if you have a fully functioning catalyist system...and ur light is on...yeah, stop messin around and buy another one. but thats not a solution for people who actually CAUSE this problem by bypassing emissions equip.

I don't have a rear o2 sensor laying around, nor the harness to plug one in into.

I made one of these eliminators yesterday, http://www.vfaq.com/mods/O2bypass.html, exactly as shown other than running a 10 ohm 10 watt, and 2x 1 ohm 10 watt resistors in series to get the 12 ohms capable of handling 12 watts (since they don't make any 12 ohm 12 watt resistors that I'm aware of). I'll splice it in in the morning.

Well the do it yourself eliminator got rid of my error codes, and I didn't even eliminate the heater signal (I'm a '95 btw, so it may vary). I made the heater eliminator as stated above ^^^ but my resistors got so hot it melted the plastic bag I threw it in (didn't have large enough heat shrink for it yet). So if you do the resistor and capacitor and still get an error code for the heater then I would try 3x 36 ohm 10 watt resistors in parallel. I did the 10 ohm 10 watt and 2x 1 ohm 10 watt in series and the 10 ohm resistor was at max load (10 watts of heat absorbed by it) and would burn you if you touched it.

So in other words... I spent < $2 to get rid of the rear o2 sensor permanently. Happy ECU, no CELs...

I can't believe how much people are able to sell these eliminators for.

It worked, if your rear O2 sensor is shot, then take the front O2 sensor and pipe it into the rear input on the ecu. Put a resistor inline of that connection to the ecu using the resistance outlined in the resistor mod.

I passed emissions doing it that way.

FUCK!!!

I went to Casper's website to get the o2 Simulator and look!

https://www.casperselectronics.com/Merchant2/merchant.mvc

Read the top of the page. :'(

Originally posted by ner947
I had an interesting discussion at the Shootout with Bill and a bunch of other people about just this. The rear oxygen sensor DOES have an effect on peformance. It's there mainly to test the efficiency of the catalytic converter, but we all came to the conclusion that the ECU probably treats an oxygen sensor failure as a global error, regardless of which oxygen sensor is stuck putting out one voltage level. The rear sensor's voltage should always be lower than the front one. This means the catalytic converter is working. The ECU will also check to make sure that both sensors are changing value, and that they are not stuck at one voltage. Therefore, if the rear oxygen sensor is stuck at one value (you have an exhaust cutout before the sensor or it's broken or disconnected) the ECU will treat it as if the front oxygen sensor has failed - it will fall back an open loop fuel map and will retard the timing. I was a little drunk when we had that conversation at the shootout. Anyone care to elaborate?

I have a bank one running rich code and my flex pipe on the exhaust is cracked letting fresh air in the exhaust before the catalyst. Guess I'll fix that first before I do anything else.

Alright, read the damn post date, holmes.