Yet another problem with th 98 Grand Marquis

When will it end? I have replaced all of the COP coils and the car runs fine. After about 10 miles of driving the check engine comes back on. Went to Autozone and they put on their OBD II scan tool. Now I get
a P0420 code. insufficient catalyst. The guys at Autozone said that miss firing could have damage the catalyitc converter. This is another $300 item with about 2 hours labor, say $440 installed. But wait, it may be the Oxygen sensors that are bad and not measuring the input/output of the catalytic converter.
This brings my total up to $2000 for intake manifold, COPS coils, and the catalytic converter.
So what do I change?
Shoud I ignore the check engine?
Also, the COP coils that I replaced today are made in China.
What is so American about these cars? The design engineering is not done in the USA, it is outsourced to India and China.
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mstrspy wrote:

I would certainly ignore it.hhahaa
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mstrspy wrote: I have replaced all of the COP coils and the car runs fine. So what do I change?
Your parts-replacing-before-diagnosing mechanic.
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