P0420

[samoedin]

Changed my cat and low stream o2 last week and my still getting 420! Any ideas?

 

[JPNinPA]

Changed my cat and low stream o2 last week and my still getting 420! Any ideas?

First did you clear the code after changing the CAT and O 2?

Did you verify no leaks at the intake? What rpm does it idle at?

Are your plugs relatively new?

Leaky or faulty injectors?

 

[samoedin]

Cleared it and it came back on. At first it was on and off now it's on for the past 2days. Right before replacing the cat I had to replace the valve cover gas kit also replaced the manifold gas kit. This morning I noticed a small leak at the end off the muffler!

 

[samoedin]

800 rmp like always!

 

[samoedin]

 

[samoedin]

I meant intake manifold gasket!

 

[JPNinPA]

Cleared it and it came back on. At first it was on and off now it's on for the past 2days. Right before replacing the cat I had to replace the valve cover gas kit also replaced the manifold gas kit. This morning I noticed a small leak at the end off the muffler!

When you replaced the cat was the old one clogged, damaged or empty?

 

[samoedin]

Hmmm it was rusty and had 200k on it! Lots of rust came out of it!

 

[JPNinPA]

Hmmm it was rusty and had 200k on it! Lots of rust came out of it!

Possibly mix the O2s up?

Leak at the intake? You replaced the gasket possibly a leak. Spray some tb cleaner or wd40 around the intake near the engine and listen for the idle to change. Also consider around the injectors. The o rings go bad. And if you pulled the rail when changing the gasket perhaps they are not seated correctly.

Pull your plugs and inspect for fouling, burning or gap. If you find something, replace it. If you find burnt or fouled plug then, Put a long handled screwdriver on the back of each injector and verify it is firing by listening for the clicking. Either clean or replace.

 

[JPNinPA]

Looked into the code meaning more. The PCM checks that the two o2 sensors are switching at different rates. Typically the front is faster than the back. If they switch at the same rate this code will be thrown. So if you haven't changed both o2 s it is possible toe front one is bad or you mixed the connections. Sometimes they make the leads different lengths so you can't mix them. Not sure on yours.

 

[samoedin]

I checked the o2s all seemed fine but I detected a leak coming right from the cat was welded (before the cat)! Could that be the reason?