1996 Ford Thunderbird catylitic converters

  • 1 POST
  • 3.8L
  • V6
  • 2WD
  • 170,000 MILES

My car was running terrible, it would not go over 40. The codes said it was a clogged converter. I decided to remove the converter and drive it loud just to make sure that it ran well without the clog. It did, it runs great. The problem is that when I looked inside the old converters they were empty. There is nothing in any of them, all three. How can it be saying it is clogged when the converters are empty, do you think the insides melted and clogged the pipe up further down near the muffler or does them being empty cause some kind of back flow?

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Tuesday, August 11th, 2015 AT 5:56 PM

1 Reply

  • 29,775 POSTS

First of all, there's over two dozen fault codes related to oxygen sensors and catalytic converters, and they mean very different things, but there is no fault code that says the converters were clogged. In fact, fault codes never say to replace parts or that they're bad. They only indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition.

Since you found them to be empty, you know there is no change taking place in the composition of the exhaust gas flowing through them, and that WILL set a fault code. I'm guessing you got a fault code related to "catalytic converter efficiency below threshold".

I don't have any vehicle history or any observations or clues to go on, so this is strictly a guess. There was a spark-related misfire and someone ignored it and kept on driving. The unburned fuel going into the exhaust system would burn in the catalytic converters where it would melt the catalyst and turn the housings orange. Based on your observation the engine runs okay without the exhaust connected, we can guess the catalyst material is in the muffler and blocking free gas flow.

You're going to have to replace the converters so those fault codes don't keep on setting. When the system is working properly, the front oxygen sensors will switch between "rich" and "lean" about two times per second. The sensors after the converters will switch perhaps once per minute or two. As the converter's efficiency goes down, the switching rate of the rear sensors speeds up and approaches that of the front sensors. Those switching frequencies are what the Engine Computer looks at to measure the converter's efficiency. With no catalyst material in there, the front and rear switching rates will be identical. The computer will suspend any other tests that rely on oxygen sensor readings for comparison, so some potential other problems may cause running problems but won't get detected. With the Check Engine light already on, you'll never know if a minor new problem gets detected that could turn serious if it's ignored.

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Wednesday, August 12th, 2015 AT 9:03 PM

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