2000 running on 3 cylinders

My stepson has a 2000 sonata 2.0 liter. About a year ago it began running on 3 cylinders.#1 was the problem.The compression and camshaft timing are right on. I replaced the spark plugs, fuel filter and coil packs and had no improvement. Now it is the # 2 cylinder that is missing and #1 is fine. I've swapped the injectors and the crankshaft sensor was recently replaced. Nothing I've done semms to work. Any ideas would be appreciated.