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Discussion Starter · #1 ·
I have a 2007, 170,000 miles, and I recently had to pull my cats because of an almost complete loss of power and pulling a P0420 code. This comes only a few days after replacing my valve covers and gaskets due to a long standing blown plug gasket (rear bank). Once I got the cats off, I could tell that one (front) was dirty and beginning to melt/erode (but would have held up for another 50K at least), and the other (rear) was almost completely ash and had dislodged, collapsed, and gotten wedged at the bottom. I believe this to be because of oil getting into my intake, not burning completely, and getting stuck to my cat. I have (had, I cleaned them today) heavy residue on the rear intakes, specifically on from the point where the PCV valve dumps into the manifold, and the rear of the throttle flap (thing? the circle that twists in the intake manifold to act as a choke in a smaller engine). I pulled my PCV hose, and it had a good bit more than a slight oil coating on the inside. Is it possible that the PCV valve could allow more than oil vapor into the intake manifold causing more problems? I know that over filled oil can escape from the PCV, but I usually do my own changes and aim for about 80% of the recommended volume.
I don't believe the PCV valve has ever been replaced prior to me. My rear plugs usually degrade faster than my front ones also.
I do not recommend doing it at home. I used everything from an impact driver, welder, grinder, large hammers, 2 cans of WD40, and a bit of blood, but I finally got the cats off. New cats (front, rear, and Y) will arrive later this week.

On a quick side note, I was able to remove one of my O2 sensors but the other is stuck and rounding off. Should I buy 2 new ones or should I be good with one old and one new? The one that was removed came out of the front, but looks more gray and tired than I would like.
 

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You might want to do a compression check first before wasting money and time on a bad block. I'll bet the three back cylinders have been scored from cat material being sucked back into the cylinders as the cat was breaking down.

The Murano engine pulls a little exhaust gas back into the cylinders, for emission purposes, on the intake stroke. When the cats start to break down, the highly abrasive microscopic particles are sucked into the cylinder and score it. Causes all the symptoms you're experiencing with your engine.

At the very least, pull the rear plugs and use a lighted scope to take a look at the cylinder walls.

Good luck.

Have a good day.
 

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Discussion Starter · #3 ·
I'll look into checking the cylinders, but what would cause the oily build up in the intake? A little, I would understand, but it was a good amount.
Also, currently our Murano is our only vehicle for a family of 5, and while we are currently saving up to buy a new Subaru ascent, I'm not ready to overhaul the engine in the hopes of having it run another 5-10 years.
 

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Discussion Starter · #4 ·
This might just be the answer.
 
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