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This cleaning process works.
I have used it several times in the past with success. I mentioned this in other threads on the topic.
The most dramatic was a 2007 Dodge Caliber 2.4 L with a very expensive "Mani-verter" that had been coked up when a failed upstream O2 sensor and a ditzy wife conspired to leave a cracked and smokey exhaust system just a month from the strict bi-annual emissions test after she drove around for weeks with an engine light on. I TIG welded the cracks in the stainless housing and followed the mild acid wash process with the only change being an initial washout with "Purple Cleaner". This caustic cleaner removed the majority of the carbon coking. The mild acid mix concentration should be closely followed as a stronger acid reaction will strip away some of your precious metal loading in the converter.
The vehicle has an upstream and downstream O2 sensor and an algorithm to check converter efficiency by comparing the two sensor outputs. It also has test cycles the CPU runs periodically by pulsing the fuel mix rich and lean in a coded sequence with expected reactions from the O2 sensor compared to the actual. This prevents a simple O2 sensor defeat device on the downstream side allowing such shenanigans as cored out cats or straight pipes.
The factory mani-verter was eventually replaced with an improved aftermarket unit, but the cleaned converter did run for several years after the cleaning process.
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