a couple of friends were helping me do my long tubes but was not sure on the o2s.......i have a 96 z28 auto and i have cats on both driver and pass side right under the manifolds......and then the other one in the middle of my car all have o2s hook ups.....would i be able to run just the o2 in each header and not have the one in the middle of my car.....i was planning on getting rid of the cats completely?

 

Yes that can be done but it will set a SES. Two options around it, the best is to have the pcm tuned and in the process get them programmed out. The second option is to use O2 simmulators.

 

You better recheck under the car.... you do not have three cats on a 96. There's one bolted directly to the drivers side exhaust manifold, and another located at the end of the passenger branch of the Y-pipe, under the hump in the front seat floor. There is no cat at the passenger side manifold.

You have four O2 sensors. There are two pre-cat sensors, one in the base of the drivers side exhaust manifold, and one a few inches below the passenger side manifold on the Y-pipe. Both of those sensors MUST be relocated to the collectors of your long tubes (unless you plan on having the PCM set up to run only in open loop).

You also have two after-cat sensors, which can be removed in the manner described in the post above. Just keep in mind, if you have the diagnostics for the after-cat sensors "programmed out" of the PCM, if they plug into your PCM for an emissions check, you will get a "not ready" on those sensors, which may fail you in some locals.

 

You also have two after-cat sensors, which can be removed in the manner described in the post above. Just keep in mind, if you have the diagnostics for the after-cat sensors "programmed out" of the PCM, if they plug into your PCM for an emissions check, you will get a "not ready" on those sensors, which may fail you in some locals.

If i do the o2 simmulators for the after cat sensors will i fail a pcm emissions check?????? what is a way for me to be able to pass with no problem?????

if i keep the plug in for the after cats and just plug the o2s in is it going to read all crazy because i dont have any cats or will i be ok??????

 

The O2 sims should prevent any codes, with the PCM showing the system "ready" when they do the emissions check. You can't leave the real O2 sensors in the exhaust system, or hanging loose. The PCM would see the unacceptable readings and set a code.

 

ok if i just get rid of the precat o2s is my car going to run like **** before i have it tuned......or will the engine light just be on????

 

I would keep the pre-cat O2's I believe they help adjust AF ratio, the post-cat O2's you can edit out and if you just pull them you'll throw an SES light.

 

If you eliminate the front O2's, your car will run exactly the way it did on startup before you disconnected them. It runs in open loop for the first two minutes or so after startup, just like it always did.... but it will just continue to run that way as long as the engine is running, since it can't enter closed loop and enable learning.

The PCM will no longer be able to use adaptive learning to alter the A/F ratio to meet the new capabilities of your engine when you make changes. If something goes a little "off", the PCM can't "correct". You get whatever the standard air/fuel calcualtion gives you. As a result, you may run rich - lost power, fouled plugs, poor fuel lmileage - or you may run lean - lost power, detonation.

For a purpose built track car, seldon driven on the street, running open loop is fine. My car runs that way. The "tune" is backed up by numerous dyno pulls, no changes are made to the setup without a confirming dyno pull, and the fuel is always exactly the same because it comes out of a 30-gallon VP Fuels drum that sits in a shed in my back yard. But for a car that is regularly driven on the street, its going to have a lot more negative affects, given the variability of fuel, the wide variety of driving conditions, and the need to keep gas mileage at a reasonable level.

Just curious.... what do you feel you are gaining by running open loop?

 

Just curious.... what do you feel you are gaining by running open loop?

well......see im not sure on running no cats and having the rear o2 sims......or just keeping my one cat and o2s......what would you do???? If i ran my old cat would i be able to use my same old o2s and have them work fine?????

 

You don't have to convert to open loop and delete the pre-cat sensors, just because you eliminate the cats.

One more time....

The two after-cat O2 sensors do NOTHING but tell the PCM if the cat is there and working. They have no affect on how the engine runs. You can delete them and have them programmed out, or use sims, and the PCM and engine will behave totally normal.

The two pre-cat sensors help the PCM control the A/F ratio. They will continue to work normally, even after you eliminate the cats and the after-cat sensors. You do not need to delete them for any reason. Your PCM needs them to control the engine, and to adjust the Air/Fuel ratio as you make small changes to your setup. The pre-cat O2 sensors have NOTHING.... ZERO.... NADA... to do with the cats, nor whether you have or don't have cats.

If you eliminate the pre-cat O2 sensors, you will possible create more problems than you solve.

It is NOT - repeat NOT - a matter of having to delete the pre-cat sensors just becasue you eliminate the cats. LEAVE THEM IN THE SYSTEM.

Whether you run cats is up to you. I built an 800HP nitroused stroker, and kept ALL of the emissions stuff intact and working, including dual 3" high flow cats in a custom built Y-pipe. All I had to do was unbolt the cats and drop them out when I went to the track and used leaded fuel.