Question

2000 Mercedes-Benz C280 2.8L V6, the injector, and coil test good. Didn't ohm plug wires. The plugs look ok too. I got the engine code P0304

Answer 1

P0304 Misfire number 4 cylinder

You can swap the ignition coil from the the number 4 to a different cylinder, if the misfire moves then you can be sure its the ignition coil

The number 4 cylinder ignition coil  is at the front. try moving it to a different cylinder.

Answer 2

P0304 MERCEDES-BENZ Code - Cylinder 4 Misfire Detected
Read more: https://www.autocodes.com/p0304_mercedes-benz.html