1 and 4 Cylineders are misfiring

I am working on a 1995 pontiac Sunfire with 2.2L engine. The vehicle has 120000miles on it and the 1 and 4 cylinders are misfiring. when I unplug the alternator, the engine runs good with no misfire. i have replace the alternator twice, using parts from two different suppliers. other parts that have already been replaced include one GM fuel pump and other from the aftermarket manufacture two GM ECM, the crank and cam sensors, the ignition module, the coils, the spark plugs and every other engine management related sensor and switch time two. i have also checked catalytic converter and timing chain. i have removed the entire wiring harness to check it for damage. some one suggested the processor in the instrument cluster might be to blame, so I changed that too. the engine still has bad misfiring that goes away when I unplug the running right again. Any help would be Greatly appreciated.