rlatulipe5591

been looking for about 2 days and cant find the answer on here, i have a 98 camaro z28 and i was thinking about gutting the cats, there is no inspection where i live but if i gut them will it cause an issue with the way it runs or will it just throw a code?

conan

iTrader: (5)

Yes, you will get the SES light. You can turn of the DTC's with HP tuners.

rlatulipe5591

i can deal with a ses light but ive been hearing so much different **** like the 2 sensors talk to each other and adjust a/f ratios and then in contrast that the rear o2 adjust nothing and all it does it measures the effectiveness of the cat

vertie

Deleating the rear O2s only deleates the DTCs, The PCM will still adjust and run in "limp mode". Scan tool will never give an "OK" for htd catalyst.

US_Army_Z28

iTrader: (3)

If your fronnt o2's go bad you willll have trouble with a/f and how the car runs, generally a rouggh idle, rear o2's just monitor the exhaust gasses after they pass through the cat. I am speaking from experience. When I first bought my 2000 z28 it had bad fronts and no cat. So I replaced the front sensors and my rough idle problem went away when I did but my ses light stays on bc I don't have a cat and haven't gotten a tune yet to get the code turned off permanently. So you'll be fine yankin the cat

rlatulipe5591

ite i got ya i appreciate the help

RPM WS6

iTrader: (3)

No, there will be no negative effect nor "limp mode" of any kind for removal of rear O2 sensors on these cars. The car will run exactly the same other than the SES light and/or incomplete emissions monitors.

My rear O2s are currently disconnected. They do nothing other than monitoring the cats.

vertie

This is the last words i'll say on this subject, i'll make it short and sweet. In the early 2000s, Casper came out with O2 simms. We got a set and plugged them into a bone stock, perfect running, WS6 TA. Took the car out and it had a noticeable loss of power at WOT (wide open throttle). No SES light but readings on the simms were rich/lean rich/lean constantly! The PCM simply thinks something is wrong and tries to compensate. Took the car back and plugged the sensors back in, went back out, power was back at WOT. Next, we tried the spark plug extenders, moving the sensor out of the pipe. Loss of power again at WOT, gasses were trapped around the sensor and readings stayed rich. Next, we drilled a 1/32nd air bleed hole in the extender housing, then, we were too lean. Next, we plugged the holes and put a piece of catalyst in the housing, again, loss of power, too lean. The only simms that work, are the electronic ones that tap into your pre cat sensor and adjust the post cat sensor readings accordingly. But the folks that came up with them, were told they're going to jail if they produce or sell any of those! Bottom line, if your cats go bad, get a set of high flow cats. Your car will be happy and the air will be cleaner! IMHO!
PS If your not racing or anything, you'll probably never notice the difference without your cats, and the SES light for the post cats turned off. Like the f-body manual says, the post cat sensor plays a "limited role" in fuel management.

z-maro

iTrader: (18)

So your saying that everyone here running cat-less exhaust with the rear O2's tuned out, is loosing power? How is it that numerous LS tuners have not picked up on this over the past 14 years?

RPM WS6

iTrader: (3)

This is interesting because I have used O2 sims on two different LS1 cars ('00 WS6 and '02 Z28) and neither one lost a single ounce of power at WOT or anywhere else while doing so. My personal experience has been completely the opposite of yours.

Yes, this is how they work, so that the PCM always sees a difference between the front and rear readings, thus fooling it into thinking that the oxygen storage capacity of the cat is within the preset threshold.

No, there is no PCM compensation for this. Rear O2 readings have no effect on A/F ratios or power or anything of that nature.

NO! You would never want a sim that plugs into the pre-cat sensor. You need an accurate O2 sensor for the pre-cat location. Sims for the rear only. I don't see any way possibile that a sensor plugged into the pre-cat location could "adjust" post-cat readings. This doesn't make any sense to me at all.

What manual? I have never seen this in the factory shop manual under any of the sections that refer to the B1S2 or B2S2 sensors.

Anyway, the rears play no role in managing the A/F ratio. When I disconnected my rears, I observed no change at all in MPG, power, or anything else.

vertie

Wow, you folks sure get wound up on this issue. I didn't make it up, I just verified "it's true". Take a GM / F-platform / service manual, look under "Powertrain Control Module", then "description 5.7L" then page through to "Catalyst Monitor Heated Oxygen Sensors". I just grabbed a 99 manual, book 2, page 6-1987.

RPM WS6

iTrader: (3)

I don't have a '99 manual, but I just looked it up in the '00 book. Book 2, Page 6-1935:

"In addition to catalyst monitoring, the post heated oxygen sensor has a limited role in controlling fuel delivery. If the post HO2S signal indicates a high or low oxygen content for an extended period of time while in closed loop, the PCM adjusts the fuel delivery slightly in order to compensate."

If you are using O2 sims, this would be a non-issue. Note the statement, "If the post HO2S signal indicates a high or low oxygen content for an extended period of time..."; such will not be the case with O2 sims, as they constantly swing back and forth from lean to rich to simulate readings necessary to pass the catalyst test. They do not spend an extended period at a high or low value. The statement is very clear about it needing to be an "extended period". I am not sure what caused the condition you witnessed with your test using O2 sims, but I've personally used them on at least two of my personal LS1 vehicles as well, and I did not see any change in fuel trims, MPG, WOT power, nor driveability.

Countless people have disabled/removed their rear O2s without issue. I suppose COT (cat overtemp protection) might be an issue here, but most turn that off when they delete the rear O2 codes.

vertie

And just to be fair, we never removed the cats, we were only interested in the PCM response with different simms. We had negative results with all, except for the 3 plug version that tapped into the pre cat sensor cable. And we weren't allowed to keep them. I don't know the benefit of your cat removal, you may be better off that way, but in our tests, it did effect our WOT and slightly adjusted STFT. Again, just our results on a bone stock car.

RPM WS6

iTrader: (3)

I've used sims both with and without cats, always without a problem. High flow cats will often not meet the efficiency threshold, so using sims or toggling off the DTCs would still be fairly common. One of my cars currently has 4-pin sims in the post-cat location with cats still in place (needed due to efficiency threshold issues), and I experienced no changes at all with WOT/fuel trims/anything else. I would never plug any kind of simulator into the pre-cat locations.

vertie

Maybe the sims your using today are better than the ones we used in the early 2000s? I would like to test a set if they are stilll available. As far as the ones that plugged into the pre cat sensor, they only monitored the MVs and adjusted the post cat sensor reading with less MVs, just like you see if the cats in place. No effect on pre cat sensor at all.

RPM WS6

iTrader: (3)

The current set I have are from site sponsor Speed Inc; I saw no change in power nor fuel trims with them installed. I don't know who manufactures them, but they definitely look different than the older style ones from the early '00s. I too had a set of the old style ones back then, and I was using them on an '00 car. Honestly, I did not witness any of the power loss that you did even with the old ones, so I'm really not sure what would explain our competely different results on this.

vertie

It's been 10 years but you have me a bit interested in this again, has anyone tried: (codes turned off in the PCM and NOTHING plugged into the post cat sensor plugs)? just curious what the PCM does with that.

US_Army_Z28

iTrader: (3)

Not sure what the pcm is "Doing" with it but I have my post cat sensors unplugged and had the codes turned off simply bc I got tired of staring at the check engine light, I did not gain nor lose any power or fuel mileage in doing so.

z-maro

iTrader: (18)

Yes, this is what most people do that run a ORY.

RPM WS6

iTrader: (3)

I would imagine that the PCM recognizes that there is no activity from the rears at all (and thus would normally trigger the MIL, but doesn't because it's toggled off....although the DTC still runs, just no MIL upon failure), and conclude that the rear O2 data is faulty/corrupt. At that point, for the purpose of A/F management, I imagine it would just disregard any data (or lack thereof) coming from the post cat points. Based on the wording in the factory service manual, it sounds like the PCM would have to see a high or low value for an extended period of time from a sensor that is known (by the PCM) to be functioning before any of this "limited role in fueling" would come into play. This probably explains why so many people don't have any issues at all by just removing the sensors completey.

As for the O2 sims, they are constantly cycling from lean to rich, never spending any extended period of time at a high or low value. So they should not cause any issues in this regard either, based on the wording in the manual (and they haven't for me, nor anyone else that I've ever known to use them).

It seems that something very strange was going on with the car you tested. There is also the possibility of A/F adjustment due to COT (cat overtemp protection). I believe that most people turn this off when they delete the rear O2s. I wonder if you somehow stumbled upon COT intervention during your test of the sims, and this might account for your results?