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O2 bypass mod, what a difference!

This is a discussion on O2 bypass mod, what a difference! within the General Help forums, part of the LSx Technical Help Section category; I have always noticed a "rumble or shake" around 80mph, I wasn't throwing codes so I figgured it could be ...

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    O2 bypass mod, what a difference!

    I have always noticed a "rumble or shake" around 80mph, I wasn't throwing codes so I figgured it could be the drive shaft or tires or something. I reciently started throwing the 430 code for the cats and decided to try these O2 sims from ebay.... I put them on and now there is no "rumble or shake" at speed and I can really notice a gain of peppyness through the gears. I'm sure I was running off the air/fuel mix even before I was getting the 430 codes.

    http://cgi.ebay.com/ebaymotors/ws/eB...m=110055004455

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    Senior Member SeVeReDiStOrTiOn's Avatar
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    You put those in for the rear 02's only right? If you put them in the front then take them out...if it's even possible for the car to run in the sensor 1 positions.

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    I hate to say it but that's false advertising, and from the picture each is but a single resistor - no way it can simulate a fully functioning O2 sensor.

    return your vehicle to the perfect (14:7:1) air/fuel ratio when you remove your catalytic converter or if your converter is bad.
    If used to replace the 2nd O2 sensor as they imply they'll do nothing as the mixture is only adjusted by what the PCM sees from the first O2 sensor. Also - your engine will burn up over time if run at 14.7:1, that's just too lean for anything other than idle.

    My guess is these are supposed to be wired in parallel with the 2nd O2 sensor signal and ground wires. If the value of the resistor was properly chosen they may fool the PCM into not setting the code for a bad cat but over time the code will return after the PCM runs one of its occasional tests.

    They also say you can remove the rear O2 sensor, however if you don't leave it plugged in the code for an open heater is going to set.

    Do yourself a favor, figure out why your car isn't running right with the factory stuff all in place. You could have a dirty first O2 sensor, or bad plugs/wires or any number of things causing the mixture commanded to be less than ideal.

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    this makes no sense. one of the main reasons to have O2 sensors behind the cat is to monitor CAT efficiency. why would you want to hide/ignore possibilities of missfiring or having a pluged CAT w/ a resistor that is fixed? id want to know why there is too much O2 comming out or why there is up and down voltage after the CAT in general. how does the ECU not detect there is a problem when not seeing any fluctuation from the rear 02's? i know they dont change much but codes are set when the ECU doesnt see any change (if i remember correctly, i could be wrong).

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    Senior Member Too Fast's Avatar
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    Not sure how the O2 sims work, but the only reason for the post cat O2 sensors is to monitor cat efficiency. They do not alter fuel trim or check for misfires.

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    True, the PCM expects to see some occasional variation from the base value of 0.450V and will, on occasion, force a test of its own by throwing the mixture rich for a moment to see if the voltage from the 2nd O2 sensor rises at least a little. If I recall it also expects a certain response and recover time.

    We've got a design that can truly fool the PCM but it's a bit more involved than just a few resistors, probably have it in production in a couple of months.

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    The O2 Sims are to replace only the rear O2 sensors. These sensors monitor the exhaust emission output of the Exhaust system. If you replace the front, the ones up by the Exhaust manifolds - in front of the Cats - the computer will not function properly and you will begin to see all sorts of problems. The computer uses info from the front O2 sensors to regulate and make adjustments for engine performance. It can't do that if you have replaced them!!

    Also of note: make sure you retain you old rear sensors because when it's inspection time, if they look they will find the Sims and you won't pass the inspection!!

    Mike

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    Member 408WS6's Avatar
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    I agree with the above. Find out for sure that the O2 Simms are on the rear sensors and not the front. You could really burn up your motor if the Simms are on the front and causing the motor to run too lean. The lean condition could explain the increase in performance (for awhile anyway).

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    Quote Originally Posted by Too Fast View Post
    Not sure how the O2 sims work, but the only reason for the post cat O2 sensors is to monitor cat efficiency. They do not alter fuel trim or check for misfires.
    YEAH.... ...The ONLY reason the rear/after cat 02's are there are to tell the computer if they[the cats] are working or not.....these will NOT make the engine run smoother or cleaner or ANYTHING...The fronts 02's HAVE to be in place for the engine to operate. ...DO NOT put 02 sim's on the front.
    99 WS6 M6 NBM !Cags,!Cats,Vinci/Crane,Hurst,Detroit TruTrac,3:73,31 Splne,Edel.Race LT's,ORY,QTEC,Flow,ARP,Percy,MSD,SLP,AC/DELCO,Bosch,GMPP,Cntrfrce DF,Htchkiss,Susp.Tech,Lakewood,285's,Bilstein,Pro-kit,SLP,RK Sprt,A/Meter,Red Optima,Magnaflow S/S Tips,Hd Pins,Tint,Fire.Ex,[*4 Hot Rod Power Tours*]

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    Actually the engine will run without the front O2 sensors but not very well, it'll be in open loop with the PCM making its best guesses at fuel and timing from the other info it's still getting.

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    thanks for the replys. Here are again what I notice with the O2 sims (yes they are on the back not the front cats) , I no longer get 430 codes and I really think the car is running better , mostly notice at 80 mph. I am checking the gas mileage and may be getting better gas mileage but I am still looking at that. Also if what I am hearing is that there is no real affect on the rear cats performance wise then whats the problem with bypassing the codes other than emmissions, we dont emission test in FL?

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    Senior Member Too Fast's Avatar
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    Quote Originally Posted by markzman97 View Post
    Also if what I am hearing is that there is no real affect on the rear cats performance wise then whats the problem with bypassing the codes other than emmissions, we dont emission test in FL?
    Not exactly sure what you meant by that question. I think when you say "on the rear cats" you really mean on the rearO2 sensors. So, if you can edit your ECU to ignore the catalyst efficiency codes, do that and you don't need the sims. You could also (I believe) get your ECU to ignore problems with the rear O2 sensors the same way, by editing (reprogramming) it.

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    To boil this all down I somehow doubt adding those sims had anything to do with fixing your problem at 80 mph. I'd also venture to guess unless you're real lucky you'll be seeing a code for the cat(s) not working sometime in the near future.

    About 6 more weeks and we'll have some true 2nd O2 spoofs out on the market, however the only thing we can claim is that you won't set a code for a bad or missing cat.

    Since they also sample the signal for the 1st O2 sensirs we could include an option to tilt the PCM towards a leaner or richer mixture but most people just tweak the PCM's programming or the MAF signal to do that.

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    MSG Crusty SPECOPS94's Avatar
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    From what I'm aware of, because I checked into this previously with a 99 Camaro, if you run the Sims instead of the rear O2 Sensors, the Sims tell the ECM that the CATs are functioning correctly. You would not therefore recevie any error codes because the SIMs fool the ECM by giving correct readings. Steve is correct in saying that replacing the rear O2 sensors you did not gain performance. Those O2 sensors merely monitor the CATs/Exhaust gases to ensure that they are within legal limits. THE FRONT O2s ARE A MUST!!
    Mike

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    Ummm...rear O2's have no effect on fueling or overall performance as stated multiple times above. They merely check to see if the cats are working properly. If you have cats and got a DTC or SES light from the rear O2's, then your cats are probably on the way out. You can check by switching the O2's from one side to the other. If the code follows the sensor to the other side, then it's the probably the sensor and not the cat. If the code comes back up on the same side...it's probably the cat. If you don't have cats, then the purpose would be to kill the SES light so if you get a DTC from some other part of the car later....you will know because the light will come back on. If it's already on, how will you know you've accumulated additional DTC's???

    I'm hoping (for your benefit) that's not your product you're selling on ebay. Non-sponsor advertising will get you banned on here. I only say that because of the low post count...not trying to offend.
    Last edited by SSpdDmon; 11-16-2006 at 09:02 AM.

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    I think we've all pretty well summed it up. While I'm unusre about every GM make/model/year I do know most will eventually figure out the simple spoofs.

    Oh, and if your reference to "advertising" is referring to me - yes, I am a sponsor. You'll notice our IEC banner on occasion but we'd never try to pass off a couple of resistors as an O2 spoof or the old IAT sub that supposedly gives you 10 HP. :-)

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    markzman97 - you're past 80K miles and out of warranty for the cats?

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    Senior Member Too Fast's Avatar
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    Quote Originally Posted by 2001NBMZ28 View Post
    markzman97 - you're past 80K miles and out of warranty for the cats?
    Catalytic convertors have an 8 year 96,000 mile warranty. If it is plugged or failing its' efficiency test the dealer will replace it for free.

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    96K? Maybe it varies from state to state? Mine says 80K in the GM booklet but heard people in CA were told only 70K sometimes - it's supposed to be a "federal" emissions warranty??????

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    I thought (from questionable reading over time) that a cat has a 5 year warranty by federal law - at least there was some sort of law that you couldn't replace your cat with an aftermarket one before 5 years unless it was proven defective or physically damaged.

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