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Po300 problem related to cats?

1687 Views 4 Replies 4 Participants Last post by  LongJohn
Hi all, I'm quite familiar with these forums... recently finished an ome HD setup with bilstein 5125 in rear that I'm very happy with. Pretty stiff but i like it and no more bouncing around. What I'm struggling with now is power and cel code...

I have a 2007 nissan frontier with 165k. Was getting just p0420 code for the last 500 miles. Would come on every 30-100 miles. Didn't notice any issues with truck so I took apart intake and checked for vacuum leaks and couldn't find problem. Now ive got constant p0300 code with flashing cel. Diminished power especially in high rpms. I can keep the light off if I keep the rpms below 2k and don't ask for much power. Also noise under drivers door and rattling. I barely drive truck now I'm just worried about hurting motor I know when cel is flashing it is not good.

Replaced spark plugs with new ngks. Old ones were all burnt on white part and from what I read well past they're use. I'm 2nd owner on truck. Took apart exhaust as I'm thinking the primary cat is clogged. One bolt stripped out so I'll cut it off tomorrow. No rotten egg smell and I'm just not sure if I'm going down the right road. I plan to remove cat or open gap and see if it keeps misfiring...

Anyone had similar problems or more knowledge it would be much appreciated.
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Check this out. Read the whole thing:

IiRC, it ended up being the secondary cat clogged.
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