Why is engine miss firing only on cylinder 3 and causing engine light to flash. on 1996 Pontiac Bonneville

Changed plugs and wires, rotated solenoid packs and still showed 3rd cylinder, replaced fel injector and checked wing harness

All for #3!! Check for cracked spark plug porcelain insulator may have cracked on install, check compression, check for injector pulse with noid light, check for vacuum leak and kv @ plug wire.
POSSIBLE ignition module circuit, kv test should reveal any spark problem! If kv tester not available, spark should jump a 1 inch gap on this system!! Can use phillips screwdriver in plug boot, just dont get near the shank. Also can use long screwdriver placed onto injector put ear to handle and listen for injector clicking to confirm pulse, if no noid light. Need compression tester! One of these test will reveal the problem.
We've checked plug, compression was near 140, injector harness reads 12 volt and we're getting a pulse. we reversed two of the solenoid packs to see if misfire changed to different cylinder but remained the same.
check EGR system, and ignition timing. compression is good so next possibility is damaged valve spring or a sticky valve.
IF YOU HAVE 'PROPER' COMPRESSION, FUEL, AND SPARK WITH NO VACUUM LEAK THE CYLINDER HAS TO FIRE!! EGR or Timing will not cause one cylinder misfire, timing is not adjustable,ECM controlled! Valve problem will result in low compression even if not opening correctly. Have a MECHANIC wit a 'real' scanner take a LOOK. At this point that's all you can do!
1 more answer
you may have damage in threading for plug(crossthread maybe).