Question about 1999 Chevrolet Blazer

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Chevy Blazer P0303 and P0420

I have a 1999 Chevy Blazer, the check engine light (p0420 - catalyst efficiency below threshold) came on about 6 months ago. A mechanic told me not to worry about it. This morning the engine starting missing and a new code appeared (p0303 - cylinder number 3 misfire). I replaced the plugs and wires but this did not fix the problem. Is this all due to the catalytic converter?

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Most probably and if a cat is not flowing proper is causes back preasure that can result in sticking or burned vavles,mechanic not nice by saying ignore the cat effiency code p0420.Can ussually have cat replaced at aftermarket muffler shop for approx. $200 cheaper than valve job or excessive fuel that you have used and damage that may occur to your engine.

Posted on Jun 16, 2009

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My 98 gmc gimmy has cylinder misfire and run rough

Posted on Aug 12, 2011

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Hi and welcome to FixYa!

Code p0420 means Catalyst System Efficiency Below Threshold (Bank 1). This will surely needs attention to resolve the problem.

Hope this helps and thank you for using FixYa! Have a good one!

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