Help! 1991 Buick PA with nonfireing number 3 cylender.

Ok guys I have a rather simple question about this 1991 Buick Park Avenue... It has a distinct miss that is causing the belt tensioner to chatter. The miss is prevelent through the RPM band as well. I have changed the tentioner (just in case) and the coil packs (due to the number 3 cylinder not fireing). I have also changed the spark plug wire (from a good doner) and the spark plug itself. I cannot figure out what to change next...and Im tired of throwing parts at this thing. I am wondering if the crankshaft positioning sensor would cause this or if it would be the Multi-spark Ignition Controller (the box under the coil packs).

Welcome to AF. Do you have spark to that cylinder, if so, disconnect the injector connector see if the miss changes, listen to the injector see if it is clicking use a long screw driver, basic diagnostics steps. Post back results. Icm and sensor will not cause a single cylinder misfire

I had the same problem on my 1991 and I changed the board under the coil pack its like 95 bucks but it fixed the problem right up. hope this helps