2003 exhaust manifold replacement

ToddK

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Mar 14, 2018
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West Virginia, USA
Looking for recommendations or experiences with replacing the exhaust manifold with the 2 cats on it. The current manifold has the media hollowed out of the cats so it’s running like shit and throwing O2 codes. Smells like it’s running super rich which I assume is because the computer is telling it to because of the sensors not communicating properly but I honestly don’t know for sure. What’s the best brand to go with? Magnaflow looks like the most expensive but is it worth the extra coin?
 
The hollowed out pre cats will not cause the engine to run rich or poorly unless the materials ended up in the main catalytic converter or damaged the O2 sensor.
Do you have cracks or leaks in the exhaust manifold; this would cause the engine to run a little rich.
How old are the O2 sensors; slow responding sensors could make the engine run rich.
There are many problems that could cause the engine to run rich; a thermostat and coolant temp sensor not operating properly are to name just a few.
 
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I'm with @CharlesHS. My Jeep was doing the same things the OP is describing. My issue was a major exhaust leak just before the O2 sensor. It was drawing fresh air into the exhaust system and giving the O2 a false lean condition, resulting in lots of extra fuel being dumped in.

I'd focus on testing the exhaust system for leaks between the cylinder head and the cats. You might have a cracked manifold but it might just be a bad donut gasket.
 
@CharlesHS @SvtLdr Forgot to mention I’m pretty certain it doesn’t currently have any cats on it, only 2 resonators.
Your 2003 had 3 catalytic converters from the factory. 2 upstream, 1 downstream.
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Your 2003 had 3 catalytic converters from the factory. 2 upstream, 1 downstream.
View attachment 305863
Correct, it currently only has the 2 hollowed out cats and nothing else except 2 custom resonators. The PO was going to try and use a tuner to delete the cats but that’s not an option for me. I’m trying to start with the 2 cats below the manifold first to see if that remedies all the O2 codes I’m getting and perhaps in the process will make it run better.
 
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