2004 Silverado 5.3L fouling plugs on driver side

[Sparky]

I'm working on my coworker's 2004 Silverado 5.3L. Long story short, it is a mess lol.

His brother in law changed the fuel pump for him (massive rust hole in the top of the pump) and also worked on the PCV valve. Well, long story short, the pump leaks around the tank seal (I think I see the cause, working on that), he ripped the non-replaceable PCV valve out of the cover and somehow swapped it, and now the truck runs like utter crap.

It has codes P0300 and P0135. Pulled the plugs and they're all way past due and very worn, and driver side plugs were jet black. Put new 41-110 plugs in it, fired it up, and it ran great! For a little bit, then started sputting and back to throwing misfires all over. Pulled plugs again, and all the driver side plugs are covered in black soot.

Brought up Torque and bank 1 sensor 1 is barely wobbling around at 0.1v. Bank 2 sensor 1 is very lazy. OK, so I'm going to go ahead and swap both upstream sensors (wish me luck lol). But, is there anything else anyone can think of that could lead to just one bank fouling out the plugs so bad?

 

[littleblazer]

How did the passengers side look? I don't really know the system that we'll but if they're on the lean side I'd look to see if there's an issue with a crossover pipe of some sort on the rail then go from there? If the sensor is that bad that's probably the starting point though.

 

[Mooseman]

Leaking intake manifold? These engines are supposedly famous for this. Maybe check with carb cleaner. If one side is leaking, it may be overcompensating on both sides. Just a theory though.

O2 sensors are a good start.

 

[Sparky]

Passenger plugs are normal. Old ones were very worn from being way overdue (by like 40k miles lol) but normal wear and color.

If the intake manifold was leaking wouldn't that be more of a lean condition, and affect both sides? Of course, knowing how this truck has (not) been taken care of, it could be a combination of everything that just need worked through one at a time.

I'll get the sensors done first, then go from there. Those should be fun enough lol.