ukshocker

I think one or all of my Catalytic Converters are clogged/stopped up. Having it inspected on Monday. Assuming it is, anything to be weary of if I remove any of them? I'm in NC so don't need them for inspection. Trying not to open up Pandora's box with O2 sensors, check engine lights, needing to re burn computer, etc. Wanting to do what's most beneficial for my engine so that it runs at it's best but keep things simple at the same time.

I think since it's OBD1, no O2 sensor on cat.

Don't want to spend a ton of money on exhaust modifications that I will regret if it causes a bunch of complicated other problems. I am a ok if I end up with more of a growl from my exhaust but not looking for any "drone" or obnoxious sounding car either that's going to get more pulled over / **** off the neighbors. Thanks for any advice or experience.

Todd
1995 Corvette base model

81c3

Simple answer is just buy stock type replacements or hi flow cats from Magna Flow or similar.... Without cats the fumes will be strong and uncomfortable when you idle or come to a stop with the top off or windows down. Not to mention, its a federal crime to remove any emission devices from any automobile.

aklim

Which one? The pre cat ones near to the engine or the main cat? IDK what the issue is but assuming they are really clogged and it is the rearwards one you can remove that and even install a more modern one to replace it and probably not have too much drone.

c4cruiser

If a shop gets caught removing a cat, they could face up to a $15,000 fine If you can do the work yourself, that may be a better/cheaper way to go. There should be an O2 sensor somewhere in the exhaust system; maybe downstream from one of the cats?

aklim

OBD would be soon after the headers. OBD2 would be in or a little after the cat. Usually after.

sluggballz

There are three O2 sensors on a 95. One in front of each cat (upstream) and one behind the passenger cat ( downstream). The cat on the passenger side of my 95 convertible went bad, the matrix was broken into chunks and was rattling around and clogging up things. I ordered a replacement from Rockauto, fit well. I replaced it myself, if I had it to do over , I'd probably pay to have it done. I'm in SC and we don't have inspections, but I wanted to keep the cats on the car anyway.
The downstream O2 was removed when I replaced the cat and the bung was plugged. It doesn't set any codes if it isn't there.
Have fun with whatever you do!!

aklim

While it doesn't set any codes because it isn't there since it is OBD1, what does the downstream do exactly? It has to report to the ECM obviously so is something assumed or what does the computer do with the values it gets? On OBD2 it is used to monitor catalytic converter efficiency but if it gets a value or doesn't, what does the ECM do? I'm not sure that "no code" means it is meaningless always.

sedgwick24

Had issues with an old Mini so I know more about O2 sensors than I should. Post cat sensors will monitor for the efficiency of cats themselves. There is a noticeable difference in oxygen content after the cats. If they are reporting a different number, the ECM will actually try to adjust fuel trim levels just like the pre-cat sensor data does. Not sure if its the same for these years before OBDII but that's how they have been required to work by federal mandate since OBDII.

aklim

OK. That I definitely agree with

Can you cite the source for that? Most of the brief looks I took a while back on the downstream O2 sensor said it was for catalytic converter efficiency. I didn't read anything that said it can affect fuel trim

I don't think they had rear O2 sensors for many of them till it got close to "change time" in 96 but I could be wrong.

sedgwick24

Here is an article from Tire Review magazine that explains what O2 sensors are and how they operate. The post catalyst sensor is the exact same sensor as pre catalyst. With my mini, the only code I was getting was "post catalyst system to lean." I found out that the issue was coming from the high flow cats that were simply cooling the post catalyst O2 too much so it thought there was too much oxygen and would dump fuel in. Car always smelled like too much gas.

https://www.tirereview.com/the-role-...-need-service/

There other thing I have been trying to convince the wife to let me buy is the Bosch handbook that goes over all components that they produce in detail plus like the theory of operation in detail.

aklim

I pretty much agree with much of the article except that I have seen a couple vehicles that have a Wide Band up front and a Narrow Band downstream. Many have the same sensor upstream and downstream except for the harness. I don't agree that the sensor will last forever with the right mixture. Past 100K, hard to say. They have been known to get old and lazy.

Here is the interesting part. While they might be the same sensor, what does the ECM do with the data from the downstream. AFAIK, it sends a signal to the ECM which the ECM compares with the upstream. In the case of your Mini, ASSUMING it is a heated O2 sensor, which most I have seen are, how do you think it is too cool? Maybe it means the ECM has seen that the downstream reports the cat being too efficient and thus it thinks something is wrong. I would think that it is a "Window" thing. Too rich and the ECM thinks that the cat has failed. Too lean and it thinks that the cat is failed because it can't run that lean so it must be an air leak somewhere after the upstream

ukshocker

Thanks everyone. NC doesn't require cats on cars 1995 or older but sounds like I need to keep them. (Don't want fumes or for the car to be loud as sh&*t). Getting ahead of myself but any recommendations on a complete new exhaust system that won't break the bank that includes high flow cats?

aklim

Corsa but that is little over $1000 so not sure what to do since you didn't put a number

ukshocker

All-in, with labor and new cats would like to stay under $1,800. From what I understand Corsa is the best so maybe one step down to help with the budget. Magna Flow? Thought is, that since it is literally up on the rack getting new cats, why not go new from cat (with new cats) to the back of the car. If anyone has any recommendations, links are appreciated. I'm a new Corvette owner and never really messed with the exhaust of my other cars so new to all of this. Thanks!

Todd Shock
95 Base Model Vette

aklim

What's your goal for the car? I got Borla because I had a great deal but regret it because of the drone. I have no cats other than the main cat since I have TPIS headers. I also need it to be more salt resistant because I drink in winter when there is no snow so there may be salt. I also need want it to be less restrictive so as not to hamper the 383 motor. I probably should have bought the Corsa since it supposedly has no drone and may be quieter since I don't like cabin noise from either the exhaust or engine but some compromises have to be made for the acceleration I want

ukshocker

goal is improved airflow, better more aggressive sound but with no drone

aklim

Probably Corsa but good stuff isn't cheap because it can't be and doesn't have to be. Cheap stuff isn't good because it can't be.

sedgwick24

I completely agree that they will not last forever. THe environment that they live in even in optimal conditions would not allow that. I think 75k-100k is a good benchmark for replacement.

As for what the ECM does with the info I am just going off of how it reacted. Its a trade secret for every manufacturer apart from what federal regulation requires that they do. This Mini had a complete new exhaust and I did a (backwards) smoke test and had no leaks in the exhaust from headers out. I knew it was dumping more fuel into it because I had a scanner and was watching the fuel trims on quite a few drives so I knew that it was at least trying to react and compensate. By "too cool" i was meaning with the heated sensor it was showing too lean (by way of increased air flow) but I am convinced that it was the high flow cat. I got tired of chasing gremlins in that car so I sold it to a guy in a non-emission county and washed my hands.

aklim

If the exhaust is too cool it is unable to run the O2 sensors because it can't get up to temperature for it to work effectively. That is why it has a heater. To get it to temperature