Originally Posted by NGM
While the engine is running unplug the injectors one at a time.. Not the coils, as the cylinder with gas foul the plug... If the engine RPM drops when you unplug an injector, plug it back in and go to the next cylinder. IF the RPM stays constant then you know which cylinder is not firing. I really reccomend replacing all the coils as they are all the same age and they will start to fail close together.
Does that work for a 2001 ford f-150? Is there somewhere online that I can see how it is done?