Driving without catalytic converter

  • 4.7L
  • V8
  • 2WD
  • 225,000 MILES
Where I live at no emissions testing. Last year shop told me I needed to replace both catalytic converters for around $1,500.00!
Way out of my budget.
Long story short, I been driving since than, without converters my vehicle drives good other than a strong rich exhaust smell.
Besides buying two new catalytic converters does anyone know how or what I can do to trick vehicle's computer to even out or to slow computer compensation of fuel. Thank you
Do you
have the same problem?
Tuesday, May 11th, 2021 AT 3:47 PM

1 Reply

First, here's links to some articles that may be of interest:




And tis video"


Running rich is not an issue of the catalytic converter. It likely is, however, the cause of the failures. The rich condition must be solved first, otherwise it will damage new converters.

On all fuel-injected engines since before the mid 1980s, an oxygen sensor has been used right where the exhaust leaves the engine. The Engine Computer pulses the injectors open just long enough to create a slightly-rich mixture, then a slightly-lean mixture. It switches between those two states roughly two times per second. The average is a perfect fuel-to-air mixture. During the lean times, the excess, unburned oxygen is stored in the catalyst material. During the rich times, the excess unburned gas mixes with the stored oxygen and is burned. The computer works to make the exhaust gas as clean as possible, but there's always still some pollutants that are formed. Those are what are cleaned up by the catalytic converter.

Starting with all '96 models, a second oxygen sensor has been added right after the catalytic converter to monitor its efficiency. While the front O2 sensor switches between "rich" and "lean" about two times per second, if the converter is doing its job, the rear O2 sensor will switch states perhaps as little as once every minute or two.

As the catalyst loses its efficiency, the switching rate of the rear sensor becomes faster. The worst case is what you have now with no catalyst at all. That means the composition of the exhaust gas going into the converter is exactly the same as what's coming out. No change has taken place, so the switching rate of both the front and rear O2 sensors will be exactly the same. It's by watching that rear switching rate the computer monitors how well the converter is cleaning up the pollutants. At some point, when the rear sensor's switching rate has become fast enough, the computer sets a diagnostic fault code for "catalytic converter efficiency". Since this code refers to something that could adversely affect emissions, it turns on the Check Engine light to tell you a problem has occurred.

The important point up to here is you smell the unburned gas because of an undiagnosed problem that has nothing to do with the missing catalytic converter. It did likely cause the converter failure though. Too much unburned gas will burn in the converter and overheat it. That will melt the catalyst material into a glob that restricts exhaust flow. Engine power will be real low and the vehicle may be not even drivable.

Removing the converter removes the exhaust restriction, but it doesn't do anything for the original running-rich problem. Besides the reduced fuel mileage and greatly-increased pollution, there's one more problem this can cause. There's well over 2,000 potential defects the Engine Computer can detect and set diagnostic fault codes for. About half of them refer to things that can affect emissions. Those are the codes that turn on the Check Engine light. Many of those defects are relatively minor with inexpensive solutions, but they can lead to serious or expensive problems if they're ignored. If one of these minor problems were to occur, the Check Engine light is already on all the time due to the missing catalytic converter, so you'll never know a new, different problem has been detected. You'll unwittingly ignore it and keep driving, potentially leading to an expensive problem.

One example could be a spark-related misfire. That sends unburned air and gas into the exhaust system. You would smell the unburned gas at the tail pipe and interpret that as a "rich" condition. The front oxygen sensor only measures oxygen, and it would see the unburned oxygen as a "lean" condition. The computer would respond by adding more fuel, making the problem even worse.

Besides the pollution and the smell, excessive gas can wash down the cylinder wall and remove the lubricating film of oil. Without that film, the piston will scuff and wear away, leading to internal engine damage. A set of spark plugs or wires might be all that was needed to avoid that costly damage.

You're asking the right question about solving the apparent rich condition, but the missing catalytic converter isn't part of that problem. I'm pretty sure it's that rich condition that damaged the converter. The place to start is by having all of the diagnostic fault codes read and recorded, but that presents another problem. The Engine Computer is constantly running hundreds of tests on sensors and engine performance factors. Often a test involves comparing two or more things to each other. For example, it knows if engine speed is near idle, the throttle position sensor had better be reading near closed-throttle. When a defect is detected, in this case lets say for the intake air temperature sensor, the computer knows the coolant temperature sensor should be reading the same temperature after the engine has been off for more than six hours. With a defect in the intake air temperature sensor's circuit, the computer knows it can't trust those readings to compare to the coolant temperature sensor, so some of its tests will be suspended. It isn't until the first circuit is repaired that tests on the second circuit will resume. In the meantime, if corrosion between the two terminals in the coolant temperature sensor's connector cause the readings to be too high, no fault code will be set related to that circuit.

There's always a real long of conditions that must be met for a fault code to set. One of those conditions is that certain other codes can't already be set. For your rich condition, at certain times the computer will turn on a solenoid-controlled "purge" valve to draw fuel fumes out of the charcoal canister to be burned. The instant it does that, it expects to see the front oxygen sensor see fewer lean conditions. If there's a problem with the front oxygen sensor circuit, the computer will still activate the purge solenoid, but it won't be able to run the test that verifies there's good flow through that valve. If the vacuum hose is blocked, for example, no flow would occur, but the computer wouldn't know it and it wouldn't set a fault code for that.

That explains why there may not be a fault code indicating the cause of the rich condition, but it is still the place to start. The people at many auto parts stores will read fault codes for you for free, but those are only the starting point. They only indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition. They never say to replace parts or that one is defective. When you do find a sensor or other part referenced in a fault code, it is actually the cause of that code about half of the time. Other tests will determine the actual cause of the problem.
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Tuesday, May 11th, 2021 AT 4:41 PM

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