The 2004 Trailblazer does not have plug wires. It has a coil pack per cylinder that connects direct to the spark plugs.
A 2004 Chevrolet Trailblazer that has a 4.2 liter engine will have a spark plug gap of .044 inches. The best spark plugs for this vehicle are iridium spark plugs.
If the car will not start...the spark-plug is bad.
AC Delco iridiums
The second spark plug is misfiring. Could be the coil right above the spark plug.
Huh? This would be the 5 cylinder engine? No # 6 spark plug? Or the V8? What year vehicle? Need more info, sorry
Bad plug or something is misassembled.
Your spark plug manufacturer would recommend your replacement schedule.
A swivel on the end of a spark plug socket and then an extension on that will get it out.