Misfiring + Code PO420

[bayareadude84]

Just moved to CA and have to SMOG my burban soon


it's a '01 5.3 BTW



Problems

White smoke at times from tail pipe
Slight Misfire
Ran my SCAN and only codes is P0420 bank 1


Already

Replaced all 8 plugs and wires AC/delco
New Gas Cap Stant
Replaced PCV valve Purolator
Replaced both lower o2 sensors Denso
Seafoam the gas in tank
SeaFoam the intake via Brake booster line
Cleaned intake with CFM spray


Many said its a bad cat converter=$$$$,Mechanic I ran into at orileys said its a ignition misfire issue,nothing to do with cat ???????

 

[SLCHOE]

Just moved to CA and have to SMOG my burban soon


it's a '01 5.3 BTW



Problems

White smoke at times from tail pipe
Slight Misfire
Ran my SCAN and only codes is P0420 bank 1


Already

Replaced all 8 plugs and wires AC/delco
New Gas Cap Stant
Replaced PCV valve Purolator
Replaced both lower o2 sensors Denso
Seafoam the gas in tank
SeaFoam the intake via Brake booster line
Cleaned intake with CFM spray


Many said its a bad cat converter=$$$$,Mechanic I ran into at orileys said its a ignition misfire issue,nothing to do with cat ???????

Your cat is probably bad but that is the effect of your misfire issue. I'd look at the fuel trims. My guess is you have coolant leaking into the intake runners causing misfires and thus letting raw unburnt gas into the exhaust killing the cat.

 

[bayareadude84]

Your cat is probably bad but that is the effect of your misfire issue. I'd look at the fuel trims. My guess is you have coolant leaking into the intake runners causing misfires and thus letting raw unburnt gas into the exhaust killing the cat.

Weird
I have owned my truck for about a year and have never touched the coolant and its at same level, never has gotten low ??

 

[SLCHOE]

Weird
I have owned my truck for about a year and have never touched the coolant and its at same level, never has gotten low ??

Understandable. You said "at times" not constantly white smoke. I'd look at fuel trims to find the answer you seek. Pull a plug out and see how it looks. If the electrode has crusty yellowish stuff buit up on it, that's coolant.

 

[rebl68]

like said above - sounds like cats.

verify proper o2 sensor voltage as well to confirm sensors are doing what they're supposed to.

 

[bayareadude84]

Got hooked up at a GM dealer and snuck my truck to the service dept during break time,Tech guy was cool and hooked up the GM Diagnostic scanner and Live readings showed no more misfire and BOTH cats are bad :/


So found a Maganflow 445006 on Amazon for $144 shipped each


Hopefully that solves problem and I can SMOG my burb soon,Before a "OINK" gets me lol !!

 

[SLCHOE]

Just started at a GM dealer and snuck my truck to the service dept during break time,Tech guy was cool and hooked up the GM Diagnostic scanner and Live readings showed no more misfire and BOTH cats are bad :/


So found a Maganflow 445006 on Amazon for $144 shipped each


Hopefully that solves problem and I can SMOG my burb soon,Before a "OINK" gets me lol !!

Cat's dont just "go bad". I've seen cars with 300K on them with the original cats on them running 700mV downstream flat and steady. Something took out your cats and if you don't fix that issue you will be doing the same expensive repair in no time. At a minimum, do your plugs.

 

[bayareadude84]

Cat's dont just "go bad". I've seen cars with 300K on them with the original cats on them running 700mV downstream flat and steady. Something took out your cats and if you don't fix that issue you will be doing the same expensive repair in no time. At a minimum, do your plugs.

Plugs/wires are all new AC/Delco


I remember one old plug was VERY bad and seized in the block took 25 minutes to pull out.