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Discussion Starter · #1 ·
Gf has a 2014 accent.

I already replaced the upper cat and manifold, it stalls out still and still has the replace cat code.

When I high rev I hear rattling coming from the rear cat.

The front cat was crumbling and showing damage.

So should I proceed here with the rear cat replacement? One mechanic said it's just a computer problem. Seeing the cat damage first hand I doubt that.
 

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Sounds like a good idea. If the rear one broke apart and is clogged it could be building up too much backpressure and stalling the engine that way, plus fouling the readings from the O2 sensors where the front cat is.
 

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What is the actual code?

I agree, you may have broken CAT internals. I had that on a newer Toyota years ago. It was fine at low revs, but no mid/upper RPM power and mileage dropped a lot.
 

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More importantly, where is your downstream O2 sensor located? Is it after the 1st cat or after the 2nd cat? If it's after the first cat, changing the 2nd cat shouldn't change much because it's only measuring the efficiency of the 1st cat. However, if it's located after the 2nd cat, your problem likely exists with the 2nd cat as well.
 

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More importantly, where is your downstream O2 sensor located? Is it after the 1st cat or after the 2nd cat? If it's after the first cat, changing the 2nd cat shouldn't change much because it's only measuring the efficiency of the 1st cat. However, if it's located after the 2nd cat, your problem likely exists with the 2nd cat as well.
I'm thinking it may not matter though if the primary cat disintegrated and clogged the secondary one. That would cause the exhaust gas to build up and concentrate in the area in front of it, which I would think could cause the computer to think the primary cat isn't doing it's job because the O2s would think the air coming out of the primary cat is not getting cleaned like it should.

I guess the question is whether the exhaust is making it through that secondary cat to the back of the car or not, or not freely enough to flow like it should.
 

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Discussion Starter · #8 ·
So two brand new cats, two brand new o2 sensors. Engine still runs like garbage. Looked into it and the burning oil issue is rampant among the gdi motors. Friend told me on that video it sounds like a bad rod or lifter.

Junk it or fix it?
 

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Ohhhh you have the GDI motor... Hyundai is warranty'ing them left and right because of the part throttle detonation issue leading to premature rod bearing failure. Check with your local dealership to see if you are eligible for a recall or a mileage extension on the drivetrain warranty.
 
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