P0300 code on 2002 Chevy truck 5.3L engine

Symptoms:

Rough idle with code P0300 (random misfire). When spark plugs were removed, the bank 2 plugs are covered with soot. Replaced plugs and wires and it ran briefly OK but misfired again after a few minutes.

Basic Concept:

If bank 2 is acting up, I would check the restriction first in bank 2 catalytic converter. If restricted, bank 2 will not be able to breathe causing the misfiring.

Repair Technique:

The exhaust backpressure can be checked by hooking a vacuum gage on the oxygen sensor port in bank 2. Pressure reading should not exceed 3 psi. If it does, the exhaust manifold can be dropped and see if misfiring stops. Be sure to reset the code after performing the repair.