I have a P0430 that Ive been meaning to get to with a new Cat otherwise Truck was driving fine in the morning then very rough in the afternoon with the CEI flashing.
Got it home and checking spark plugs I see oil on the threads and carbon on the tip of the plugs. So far I think I just need to replace the valve cover or the VC gaskets as oil is leaking onto the plugs?; but the covers are not coming off.
I checked the computer, its not showing any codes thrown, CEL flashes non stop, Im not driving it since getting it home.

Hope I can get advice on whats wrong and how to fix it.

 

If you just keep driving with a CAT that is triggering the O2 sensor because it is fouled by oil/carbon, poor injector performance etc, eventually it will cause the flashing CEL.

You have to look at the reason for the P0430, might not even be the Cat. When were your plugs last changed & how old are the coil packs?

Leaking oil on the plugs should not foul them, but I guess if bad enough they could compromise the connection under the boots???? I would suspect the plugs you described as a contributor, that is not coming from external oil leaks. If they are not firing to full potential or missing on occasion, then replace the coil packs, or at least the worst one(s).

When you say the Valve Covers are not coming off? Why, it is just a matter of getting everything out of the way, then removing the 4 little 8MM bolt fasteners and knocking them loose.

 

 

I changed the plugs in 2019 along with the coil packs then.
The valve covers were very much stuck on. I used a plastic trim pry bar and a mallet to wedge the covers off. The cover on driver side, which no coincidence i guess is bank 2 for the cylinders and cat, looked dirty in comparison to the passenger side.

Pretty sure the cat is bad, I had changed the sensor a year ago.
I




attached photos

Thank you and HUMMERZ both for your quick reply

 

Better view of plug 7


Plug 5

 

your better off with the real (not amazon/ebay) AC Delco iridiums it calls for 100k+ miles life span

 

That is why I do not, never ever, use those fancy new fangled super duper funky shaped ground electrode promise the world and do nothing spark plugs. Lots and lots of testing went into spark plugs when that "new design" stuff came out prior to iridium at the GM Tech center down the road and none of them could produce any measurable improvement. Replace with OEM type iridium plugs, those things are tired and dirty!

 

Them there Phancy Azz spark plugs bought you nothin' but replacement sooner than the OEM iridium plugs. +
Replace those Krap plugs with the OEM plugs properly gaped and see if that heats up the CAT enough to clear it out.
May take several heat cycles to see a change.

How many miles on the 5.3L?

 

130K ish miles on the odometer, Just changed the plugs, new valve covers with new grommets and gaskets, new pcv valve; didnt fix it. Still runs rough at idle, flashing CEL no code, rpm needle bounces.
First crank after doing all that work, the truck started worse and i smelled unburnt fuel and it threw a code: P0300. But then I found I had not reconnected the number 1 and 3 wire to the coils; I cleared the code.
Putting those wires on, truck ran rough then smoothed but didnt go back to how it should be and then the flashing CEL came back on,

I am pretty sure the coil packs are good. Im thinking a fuel injector is bad.

 

some one just had a similar issue his case was a stuck purge solenoid you can disconnect the purge line from the engine and block the engine side off for testing. you can also try disconnecting the MAF sensor for testing purposes to see if it a source of problems as well. if it runs better disconnected then either it needs cleaning or it has issues.