My girl just bought a 2004 EVO 8 129K Miles bone stock, keeps throwing a p0420 (Cat efficiency below threshold) we found an exhaust leak right after the cat before the rear o2 and fixed that gasket and cleared the code... 50 miles later the light is back on this is the 3rd time we have cleared it... What else could it be? Is it the cat? We need to get emissions soon for her tag!

Anyone?

 

Cat might be shot?

 

It definitely sounds like the catalyst is bad. With the amount of miles on it, its right around that mileage where cats go bad on a lot of vehicles. Time for a cat.

 

ditch the cat,remove that code from ecu.emission test in your state obd port only or visual/sniffer?

 

Obd... Any idea were we can find a stock OEM cat? Our local O'Reillys doesn't carry them.

 

Dealer is your best bet but they aren't cheap. Or check on the for sale section.

 

Buy a high flow performance cat from an aftermarket vendor. My car has one and passed inspection in NJ.

 

You can disable the rear 02 but force the sensor to read ready with an ecu patch. A mechanical 02 fix may work as well if you don't want to buy a new cat.

 

What is the mechanical fix?

 

Car has been rattling bad at idle thought it was a heat shield, got under it and its coming right from inside the cat :0

 

Removed the cat...its done, all broke apart inside.

 

If it's rattling inside the cat it's bad. It's only a matter of time before something worse happens like it becomes clogged. Replace it with whatever you like: high performance cat, test pipe, resonator, OEM cat depending on the level of emissions testing in your state.

Once replaced you can use a mechanical fix like a O2 sensor extender (non fouler) or you can modify the internal ecu code to disable the code/force readiness test complete unless you're using an OEM cat. Do a quick search on here. There is a bunch of info on modifying the ECU code.

 

We removed and gutted the cat, nothing inside it now... How bad will the car fail all stock but with the cat gutted? It still looks like a stock cat bolted up Lol.

 

Best of both worlds I guess. It looks stock yet is free flowing.

As for emissions it really depends on how they test in your area. If they use a sniffer it will fail badly. If not and they just use a visual/plug in test you can get around it with a O2 non fouler (costs about $5) or altering your ECU code (you'll need a cable and software to modify the ECU)

 

Spaced it with the 5$ anti foulers...thanks