i got a check engine lite today the code was P0420.
Catalytic Converter Efficiency Catalyst 2/2 efficiency below required level.
I have replaced downstream oxygen sensor and still get code after I erased all check engine light codes. I even replaced
the upstream just to be sure.
How do I fix this problem?
New Catalytic converter??

My truck it Dodge dakota quad cab 4x4 4.7L engine.
Truck has like 86,000 miles on it.
I purchased it back in 2008 and when I did the tuneup on it, looked like the factory champion plugs were not tight,
I am thinking maybe that is why the catalytic converter went bad. A vacuum gauge holds like 22hg vacuum but when I
open the throttle quick the gauge goes to below zero?
Also just recently my intake gasket went out and I replaced that. I cant remember the check engine light code was but
it was for the rpm out of range. I replaced the idle air control valve to find out that it was a vacuum leak thats why i replaced the intake gasket. (Plenum)

Any help will be greatly appreciated, thanks in advance for any help you can give me.

I purchased the last part today online from rockauto.com I purchased Walker 50209 catalyic converter and the extension
pipe Walker 56246
Hope these are the right parts??
http://www.rockauto.com/catalog/more...266&cc=1424506

 

P0420 1/1 Catalyst converter efficiency

That's a weird one with the vacuum gauge. I'm just guessing there might be an exhaust restriction causing the positive pressure.

Looks like you have the right parts.

 

Thanks for your help, I just thought that catalytic converters lasted longer that 86,000 miles.

 

One question first, what brand O2 sensor did you use? Don't say Bosch.

But, catalytic converters should last longer than that. I'm at 140k and counting...

How was the truck operated? Lots of idling? Were there any problems, mixture, etc., causing it to run rich/lean?

The plugs are a 30k change.

 

Truck runs very rich ever since i got it. Yep bosch o2s truck gets 6 to 10mpg.

 

Which o2 sensors do i get?
Just want truck to run right without po420 check engine light on.
I put on airaid cold air intake when i got it and still poor mileage. I put in mag hytec trans pan and diff cover.

 

Putting too much money in this truck. Champion iridium plugs. Wanted to stay with factory plugs but part store said iridium will last longer.

 

I have already replaced exhaust gaskets too. Kind of weird exhaust gaskets blew out. And so did intake gaskets within 2 months of eachother.

 

The iridium plugs last longer, true, but copper is more efficient at conducting electricity. There's a big debate on them but really, for how easy it is in changing plugs run the OEM RC12MCC4 copper plugs. To hell with the parts store. Dodge spec'd the plugs for a reason.

Use NTK or Denso O2 sensors, they are OEM. Lots of people have nothing but trouble with the Bosch O2's.

I'm thinking you have a restricted exhaust, yes likely the cat. Blowing out an intake gasket is weird. There really shouldn't be any pressure greater than ambient in there, unless there was a backfire.

Running rich will kill the cat.

 

The check engine light came back on po430. Now im really guessing its the catalytic converter. Check engine stayed off for 2days. When it gets colder outside it seems to set code