The Stovebolt Site Forums The Shop Area The HiPo Shop catalytic converters / 02 sensors

I'll be the fist to admit that I don't know it all. This project has taught me alot thanks to the help from you guys. That being said, I have another question to throw at you. I was talking to a patient this morning. He was wearing a Super Chevy t-shirt so our conversation quickly turned to classic vehicles. I told him what I was building and what I had done so far. He asked me about . I told him that I wasn't planning on running any. He said that they were needed in order for the O2 sensor to function properly. Please tell me this is not the case!

I don't know if that's the case or not. I have an '89 K3500 with a TBI 454. I bought this truck a few years ago and was never thrilled with its fuel economy, but otherwise was pleased with it until last November when it was totaled in an accident.

I kept the salvage for parts and recently discovered this truck has no catalytic converter. Its got a home made looking dual exhaust under it. It also has an oxygen sensor.

So my conclusion is they can function, but I don't know that it functions properly. It was not throwing any error codes that lit the check engine light.

My plan is to use that TBI 454 in my '54 GMC 1-ton, so now I'm going to need to find the same answer you are after. My project isn't far enough along adding catalytic converters is a problem, but better to know now...

i think that the guy may be talking about the 02 sensor that is positioned after the catalytic converter and not the one in the exhaust manifolds/headers. The one after the cat monitors the cats efficiency or ability to clean the exhaust. The computer monitors the post cat 02 sensor and compares the data to the pre cat 02 sensor(s) in the manifold(s). On some vehicles you can remove the cat and never have a code appear, but on others within a few driving cycles the code will appear. Ive even heard of people mounting the post cat 02 sensor outside the exhaust like on the frame and never having a problem. Otherwise removing the cat on a vehicle without a post cat 02 sensor should have no effect on the engine at all, besides a better flowing exhaust.


as a personal experience, my brother has a 94 Pontiac Trans-Am with a LT-1 and is currently running it without a Catalytic Converter. He has had no problems with it as there is no sensor after the cat. Now if his car was a new model and would have done the same thing its most likely the computer would be throwing a light. Another example is my daily driver, a 96 Pontiac Grand Am with the 2.4L I4. It has a sensor after the cat, and because the cat is so far gone, the light never goes off. Never had a problem passing yearly emission tests though.

My 96 jeep cherokee had an o2 in the cat. Removed the cat., welded a bung in the pipe for o2, runs better, better mileage, no codes.

Whew!! I'm glad to know that because if that was the case
I was seeing a carb in my immediate future!!

Your friend was referring to O2 sensors that number more than one. Some cars have as many as 4, at least one of which is after the cat. converter. Your ECM is programmed for the number of sensors required. I have one o2 sensor in the header, and things work well. The sensor starts working in closed loop when the temperature goes above 600deg. F. As long as you can generate that kind of heat in the exhaust where the 02 sensor is, it will work perfectly. Also, as on my truck, if you have dual exhaust with no cross over pipe, one sensor in one of the headers will also work OK for the entire engine.

another thing to add is if the post O2 sensor does give you problems (basically a light is all it is), you can always send your computer out to get reprogrammed. My brother sent the computer for his Trans-Am out to get reprogrammed and it only ran him around $100-150, but just removing the post cat O2 sensor wouldn't cost nearly that much, my brother had a bunch more done like removing the EGR, AIR, programmed to optimize gains from adding long tube headers, cold air intake, performance transmission and so on.

Fuel injection can run without an o2 sensor, but it runs better with one. You can run into problems, as previously stated, if your f/i system was designed to have o2 sensors after the cat as well, because you won't have one to read after. It is actually illegal to install a cat on a vehicle not designed to have one from the factory due to the heat they emit, which place wrong could cause a fire. One o2 sensor per bank is the best way to go because it will read and adjust the air/fuel ratios more specifically with more information. They can be programmed to run without, but then you're simply hoping that the air/fuel ratio is correct, but not monitoring it and adjusting for temperature, load and other variables.

Devin

In a feedback system, the O2 sensor helps the Three way Catalyst perform more efficiently. The sensor is also used in fuel system management for computerized engine controls.
To begin, optimum fuel mixture (for performance and economy) for petroleum internal combustion engine is 14.7:1 (14.7 parts air to 1 part fuel)or stoichiomentry. The computer uses sensors try to maintain stoichiometry. Granted when the engine is cold,or requires full throttle, mixture is richer. The computer mainly uses coolant temp, throtle position and exhaust oxygen to obtain stoichiomentry. The O2 sensor ranges between 0-1 volt, with 450 millivolts being center. The computer commands more fuel to the engine when O2 sensor voltage drops below 450mv and subtracts fuel from the engine when sensor voltage is greater than 450mv. For a carbureted engine, the computer controls the metering rods to add and subtract fuel. In the case of fuel injection, the computer controls injector on time. We now add the 3 way catalytic converter into the mix. A 2 way cat converts hydrocarbons(HC) and carbon monoxide (CO) into carbon dioxide (CO2) and water (H2O), the byproducts of perfect combustion. The 3 way cat is different it that it controls NOx emissions. NOx is created by temperature. Therefore the cat must extinguish the combution process. So, back to the O2 sensor and the computer. If the O2 sensor works within an optimum range of 14.5:1 (slightly rich and very little to no O2) and 14.9:1 (slightly lean and some O2), then the engine can produce the O2 necessary to complete combustion in the cat by turning HC and CO to CO2 and H2O. The rich mixture which produces almost zero O2 is used by the cat to extinguish the combustion process in the cat to reduce NOx. A substrate material attracts O2 for combustion. That is a basic computerized engine theory.

Can I assume you can run without the 02 sensor if you have converted to a carb?

No, that is not always the case. If you run OBDII fuel injection, it will trip a code in your computer if you don't have cats. But will still run fine. I rodded out the cat in my 2002 Grand Am GT when it became clogged (no smog check here), and although it lit the check engine light, it hasn't hurt driveability one bit.

If you're running an EFI that requires OBD1 instead, then you're fine without catalytic converters. An example of that would be the L98 tuned port fuel injection from a Corvette.

Doesn't matter if it is carb or FI. If your system has a computer that controls fuel mixture, then without an O2 sensor, it will never go in closed loop. Closed loop is adaptive fuel control based on the most efficient fuel demands of the engine for a given condition.

If you use a nonfeedback (no computer controls of the metering rods) carburetor, then you may run without an O2 sensor, or any of the other sensors and the computer for that matter.

Some fuel injection systems don't require a computer and base fuel demand on vacuum.

But think of the performance capabilities of using a computer to control timing and fuel mixture. Here is an example. My Grand National will give the engine as much timing as I want, so long as the engine knock sensor does not sense detonation. I add alcohol/water injection into the induction system at 10psi of boost on pump gas, with larger than normal turbocharger. The stock HP/TQ ratings for a GN is 245hp/335ft/lbs of torque at 16psi of boost. With alcohol injection I can now run 22psi of boost without any noticible detonation. The computer gives me all the timing an fuel that the engine demands. With bigger injectors and a higher volume fuel pump, I'm now in the range of 450hp and over 500ft/lbs of torque. And as a bonus, 22mpg on the freeway. When the 383 goes into my 55, I'll get a little over the HP numbers of my Gran\d National, but at 15mpg if I'm lucky.

How do you think all the major autombile manufacturers get so much HP and torque out of todays modern engines? and then get fuel economy to boot. It's a computer that controls all aspects of fuel and timing management.

you need the front air fuel sensors to help the computer adjust the fuel trim. cats are not needed. neither are the rear sensors. the rear sensors are there only to monitor the performance of the convertor.

Adjust fuel trim for what?

to keep the engine running at the optimum air fuel ratio.