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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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Your going to find that the P03OO can be a dozen different things or more. I've been fighting the same issue for weeks. My truck is not my daily driver so I'm not in a rush but will share some history.

My truck acts similar - between 3-4k rpm's CEL blinks and P0300 shows up - no other codes, just random misfire. Seems to idle fine until you hit 3-4k rpm's and once the misfire is there - the truck idles ruff.

I've replaced plugs - wires, entire distribution cap and all associated parts within the distributor (youtube PO300 and you will find lots of good info surrounding P0300 and your distributor)
MAF replaced too.

Local shop has tested fuel delivery - even compression at each cylinder - local shop was stumped and didn't charge me anything.

Went to dealership - what a waste of time! Dealership is trying to tell me its my cats that are bad and that could be true but there are no codes associated with cats going bad or rotten egg smell. I intend to rid my truck of the cats completely near future but I'm still chasing the P0300 ghost.

Truck has 129k miles on it and I barely drive it. I'm thinking its fuel related - bad injector, clogged fuel rail, etc.

My next project is to replace the fuel filter myself and take a really close look at the fuel filter. Truck is babied and hardly ever driver.
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From the Nissan Service Manual - possible causes PO300

Screenshot from Nissan Service manual enclosed


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