I need to bypass an O2 sensor

[Chryco Psycho]

I have a customer with an O2 sensor that needs to be eliminated , I need to find out what the correct resistance is when the O2 is reading Properly , anyone know what that value would be , it is an 4.2 lt v6 ford 1/2 ton , I will find out what year ,
 Thanks for any help .

[diyhemi.com]

I have a customer with an O2 sensor that needs to be eliminated , I need to find out what the correct resistance is when the O2 is reading Properly , anyone know what that value would be , it is an 4.2 lt v6 ford 1/2 ton , I will find out what year ,
 Thanks for any help .

The correct answer is there is no set resistance. Oxygen sensors are supposed to oscillate between 650-850mV constantly. At a constant voltage or soldering in a resistor to manipulate voltage, the computer of the car will recognize that the sensor is not acting properly. Oxygen sensors seldom go out instantly their responsiveness gradually fades over time . Once their responsiveness is outside of the preconditioned parameters, the check engine light comes on. The data collected over several tests with failed conditions sets the light off. That's why it takes a while for the light to go off once the sensor is replaced. (If you don't turn off the light with a scan tool)

What you need is an oxygen sensor simulator, this will give false variable readings that the computer looks for. They are little black boxes that take the place of a sensor. Then you take a plug and cap off the bung in the exhaust.

This website shows you how to build one. Note the 555 timer chip, that is used to trigger the varying output sequence.
http://www.mkiv.com/techarticles/oxygen_sensor_simulator/

Here is one ready to go "for testing purposes only, haha"
http://www.afterthoughtsauto.com/o2sim.html

[Chryco Psycho]

Thanks for the info , the truck has the Cat removed & the O2 is just dangling , it goes into closed loop & starts to run weird probably because the is not reading in the right zone from the O2 so it would add more fuel into the mix to try to get a reading from the O2 .

[msbaugh]

We put long tubes and hollowed out cats on my gfs 2010 r/t. the light kept coming on and it would lean the mixture. There are venders that sell spacers with filters in them to fool the sensor. It did the trick for our case.. I've also heard some tuners like diablo can throw the computer in a continuous loop in regards to the sensor, essentially turning it off.
Luckily out of city limits here in Texas we don't have to pass emissions during inspection

[ntstlgl1970]

Thanks for the info , the truck has the Cat removed & the O2 is just dangling , it goes into closed loop & starts to run weird probably because the is not reading in the right zone from the O2 so it would add more fuel into the mix to try to get a reading from the O2 .

What year is the truck? If it's OBD2, was the O2 after the cat or before it? there is a huge difference between the two as far as what the computer is looking for in a signal. The pre cat O2 should oscillate pretty rapidly, the post cat O2 should follow a similar pattern to the pre cat sensor (but with less amplitude) as the cat warms up, then start to steady into more of a sine wave when the cat is up to temp. Eventually it should steady out at a high voltage as the cat stores and releases oxygen. If the rear sensor has the same readings/amplitude as the front sensor after a set period of time then it sets a code. You can try screwing the rear O2 (if that's what it is) into a spark plug anti fouler with steel wool in it and the anti fouler into the exhaust to see if that will work. Sometimes it does, sometimes it doesn't.

[Chryco Psycho]

the cats are off , the O2 sensors are / were hanging from wires but have since been rewelded into the pipes looks like 2 pre cat O2s  , the truck still runs just fine until it switches to closed loop

[msbaugh]

http://www.bigdaddiesgarage.com/mini-cat-cel-fix.html

Put some hollowed out cats on it with these installed to the 02 sensors. Seems silly but it fools the computer and has worked great for me No loops no codes, thinks everything's normal

[Chryco Psycho]

Interesting idea but not cheap at $100 for 2

[Jesus H Chrysler]

I put a catless downpipe on my SRT-4.  I welded an O2 bung into the pipe and put a spark plug anti fouler in, then the O2 sensor.  It cut down on the amount of gas the sensor sees so it worked properly and never threw a code.

[mopar12372]

just weld the o2 bungs into the same position that they where before . eliminateing them isnt the answer because the obd2 system can be programmed with out them the system is useless for tuneing . yes the engine will  (run) while   defeating the purpose of the engine management system .

[msbaugh]

Chryco Very true, but as Jesus said  you can probably make your own fairly easily using the same ideas

[Jesus H Chrysler]

http://www.bigdaddiesgarage.com/mini-cat-cel-fix.html

Put some hollowed out cats on it with these installed to the 02 sensors. Seems silly but it fools the computer and has worked great for me No loops no codes, thinks everything's normal

I never saw those before!  Great idea in concept, and if the car HAD to pass a strict inspection then they're well worth it.  But my trick was to take a $5 anti fouler (which looks like the same thing minus the honeycomb) and I had to drill it out a bit so the O2 would fit.  Then the small hole at the end limited the gas the sensor saw.  Just dumb luck it was the right ratio so as not to trip the CEL or throw an emission code.  Your results may vary etc. but for $5 I think it's worth a shot?

[Chryco Psycho]

Well I ordered a pair , we will see what happens .
 Not sure what the anti fouler part looks like or where to get it , I know 4 things for sure , there are no cats in the vehicle & the O2 are still in the pipes in the original positions , the computer needs feedback from the O2s , & the engine runs fine until it warms up fully & goes into closed loop then it runs like crap so it makes sense to try this .

[msbaugh]

Well I ordered a pair , we will see what happens .
 Not sure what the anti fouler part looks like or where to get it , I know 4 things for sure , there are no cats in the vehicle & the O2 are still in the pipes in the original positions , the computer needs feedback from the O2s , & the engine runs fine until it warms up fully & goes into closed loop then it runs like crap so it makes sense to try this .

$100 seems expensive, but in my experience it was well worth it.  It's cheaper than re-installing cats and easier than messing with tuning... let me know how it goes. 
It makes sense that it runs like crap, if the o2 is plugged in with no cats, it's probably leaning out the fuel mixture quite a bit because of the unburnt fuel readings. We had the same issue on our 5.7 Challenger until I screwed those suckers on there

[Jesus H Chrysler]

Here's the anti fouler:

http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=spark+plug+anti+fouler

They are a cheater way to get a car to run when there is something seriously wrong and the plugs keep fouling.  Nothing you should use in normal repair.  People have repurposed them to limit the amount of gas that the O2 sensor sees since it has the same threads, and a small orifice at the end.  The units you bought are purpose made and have a small cat built in to filter the gas and get a more accurate reading.  To do the job properly those are the units to use.  The anti fouler trick is the quick and cheap way to get by.  The downside is it might not work on all vehicles.  I've heard they have a good track record tho.