if i replace my cat with straight pipe what should i do with the sensors,will they still read correctly if installed in the new pipe?

 

Unless it is a California truck I would not think you have an oxygen sensor after the cat so as long as you fit the one before the cat you should be good to go.
If there is one after the cat you would possibly need an o2 simulator.

 

it has an o2 sensor before, in the top of the cat, and one after.
also where would i go to get an o2 simulator for it?

 

Have a look at o2simulator.com and obd2cables.com for them.
No personal experience of either.
Another way you can go is to weld a threaded boss into the pipe for the after cat sensor, with threads for the sensor to screw in to and just long enough to keep the sensor out of the exhaust flow. I have been informed that this works well.

 

ive heard that o2 simulators arent that great for performance because then send a constant signal instead of a variable one that reads true to make air/fuel ratio adjustments for optimum performance.
i just wish there was a way to eliminate the o2s in the top of the cat and the one after. would a non california emissions pcm work?

 

looking for some cheap headders while im at it

 

Don`t know the answer to that. Some of the experts here will know, hopefully some will chime in. If not maybe ask in a new thread.

 

I'm not 100% positive on this for the truck world, but I am fairly familiar with this for Mustangs. The 1st O2 sensor (before the cat) is what the PCM uses for the A/F ratio and actual engine function. The after-Cat sensor is to ensure the cat is functioning properly and throw a code if it is not. By putting on a sensor simulator for the 2nd sensor you are just telling the computer that all is well with the cat. For my Mustang they are called MIL eliminators and I got them from Steeda (which I just looked and they no longer sell). The "tricking" of the sensors had no impact on the engine and that car gets 22+ MPG in mixed driving with either my catted or off-road pipes.

 

thats a good adea but what about the o2 sensor in the top of the cat. my truck has an o2 before the cat,one in the top center of the cat and one in the end of the cat? i wonder what the function of the one in top of the cat is and why there is one installed in the end of the cat instead if the pipe right after the cat?

 

That's strange, I've never actually heard of an O2 sensor in the cat. I'm assuming your truck is a mass-air truck so each cylinder bank would have it's own O2 sensor, can you find and identify the O2 sensors for each bank?

Have you checked to see if the cat has already been hollowed out?

 

JMC302 is on to it. The O2 sensor after the cat is compared to the primary O2 (before the cat) to see if the cat is working. Air/Fuel ratios are adjusted based on the primary O2 sensor signals. You probably have "slow" O2 sensors, some newer vehicles have "fast" O2 sensors. The "slow" ones bounce back and forth between zero and one volt (lean to rich or vica versa). The computers looks to see that on average the secondary O2 sensor reads less (or more, I forget) free oxygen than the Primary. If not it throws a emissions code. If you supply a constant voltage to the secondary, the computer knows something is wrong. It is supposed to bounce back and forth and average to 0.45 volts. The simulators achieve this with a simple circuit, but they are kind of pricey.

TRY THIS BEFORE BUYING AN O2 SIMULATOR:
This has worked for me in two out of two attempts in the past.

1.) Go the the parts store and buy a package of "Spark Plug Non-Foulers" for ~$5. It should come with two steel bung like parts with an 18 mm male thread and an 18 mm female thread(fits most/all O2 sensors). Don't quote me on the 18mm part. I've always used the shorter variety:
Motormite/Spark Plug Non-Fouler from AutoZone.com

2.) Drill one of the non-foulers out so that your existing O2 sensor will screw all the way into it.

3.) Insert the unmodified non-fouler into the O2 bung.

4.) Insert the modified non-fouler into the unmodified one.

5.) Insert the O2 sensor into the modified non-fouler.

Let her roll!

 

dosmthn said: "thats a good adea but what about the o2 sensor in the top of the cat. my truck has an o2 before the cat,one in the top center of the cat and one in the end of the cat? i wonder what the function of the one in top of the cat is and why there is one installed in the end of the cat instead if the pipe right after the cat? "

I've seen O2 in cats before, but not with one in the cat and one after. 96 Mustang GT with 4.6 has four cats with an O2 behind each cat and two primary O2s (total of six O2s) if I'm not mistaken. Do you have one cat?

I would try my trick mentioned above (I say mine, but I got it off a forum years ago) on your number 2 and 3 O2s. You may need to space the third one out an extra step to make it read better than the second. Pay attention to fuel mileage and/or Check Engine light.

 

thanks ill try the non foulers after hollowing out the cat and what about finding cheap headders the only ones ive found are about 600$. it has something to do with having the e4od that makes them so damn expensive. and 600$ is way to much to pay for some exhaust pipe welded to flanges.
by the way making my own is kinda out of the question because im a horrible welder.