QuestionQUESTION: The code that was produced is a 421, which tells me that the cat isn't heating up correctly. The cat was replaced about 18 months ago. When I step on the gas, there is very little rpm being produced, and the vehicle doesn't pick up speed very fast. I was told that there is a leak in the flex fitting that was installed to replace the catalytic converter. The fitting is between the manifold and the cat. The mechanic told me that is was tough to tell what the issue was, but they are guessing that it is a bad cat, and that the cause may have been an o2 censor. They want to replace the o2 censor and then have me go to the shop that replaced the cat and have them check it out. Others have said that it may be a fuel filter. The question is, what do you believe is the problem with the vehicle.
ANSWER: P0421 indicates the manifold catalyst on bank 1 is inefficient. Most likely the problem is with the catalyst itself.
Based on your description, it sounds like the rear catalyst was replaced with an inexpensive replacement. There are several potential issues with this:
-- If you had P0421 previously, replacing the rear catalyst could not have repaired that issue as there is no oxygen sensor after the rear catalyst.
-- Catalytic converters are expensive because of the amount of precious metal in them. It's the exhaust gases' contact with these precious metals that initiates the further reaction in the converter. A failed converter is usually worth $40 to $50 to a scrap dealer, so I conclude that $50 to $100 has little of the precious metals necessary for an efficient and long-lasting converter.
It's possible that a faulty upstream oxygen sensor or oxygen sensors with connectors switched could cause this code, but in most cases, the former would set an oxygen sensor code, and the latter wouldn't occur unless someone unplugged the oxygen sensors and reconnected, most likely within the last couple days.
The fuel filter is not a possible issue.
My advice is to return to the shop that installed the converter prior to attempting any repairs.
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QUESTION: Is it possible that the converter has clogged, therefore causing the expansion joint to blow out? The reason that I ask this, is because the flex joint does have a hole in it. The problem with the lack of power happened when that flex joint grew the hole.
AnswerI'm not certain what this expansion/flex joint is or looks like. Is this something that was originally on the vehicle, or was it added when the converter was replaced? Which converter was replaced? Is it in front of or behind the converter that was replaced?
Ultimately, if you have a significant restriction in the exhaust (e.g. a clogged converter) the pressure can cause a leak anywhere prior to that restriction, but not after the restriction. So, for example, it's not possible for a clogged converter to cause a hole in a muffler.
