[cobred]

First see if you have spark to the plugs of the dead cyls. If you do remove the plugs and swap them with the ones from known good cyls. this will eliminate the ign. system. If the same cyls. are still dead remove the plugs and do a compression test compairing the 3 bad to the 5 good cyls. If the 3 are low suspect valve timing, pushrods, cam lobes, etc.