Depending on compression and quench, go to autolite's web site. They offer an excellent AR plug for your app.
I had this very same problem with my Chevrolet Silverado. The only thing that will cure this problem is replacing all your Oxygen Sensors and running premium fuel.
from underneath the car you can get right to them
8 spark plugs
3 of the plugs are on top of the mottor and 3 of them are on the bottom side
yes they do go bad
Try replacing the plugs and wires
There are four spark plugs on each side of your 1991 Chevrolet engine. The spark plugs will be near the bottom of the engine.
I would recommend plugs, wires, high flow air filter(k&n, spectre, etc.)supercharger oil, supercharger coupler if its still stock, and engine oil.
you rotate the engine to get to the rear plugs but the front ones are easy to replace
Every gas burning internal combustion engine has spark plugs. Diesel engines do not. Your Impala is not a diesel, so it has plugs.
code p0305 is cylinder no. 5 misfire detected, and p0205 is injector circuit malfunction cylinder no. 5 good luck, I have a 99 Chevrolet venture also, they are riddled with problems.
you either did not gap the plugs to spec or you put this wires on wrong