2000 Ford Mustang P0301 Code

Check the compression and injector for that cylinder

Misfires can be caused by worn or fouled spark plugs, a weak spark (weak coil, bad spark plug wire), loss of compression, vacuum leaks, anything that causes an unusually lean fuel mixture (lean misfire), an EGR valve that is stuck open, dirty fuel injectors, low fuel pressure, or even bad fuel.

Check the compression and injector for that cylinder - Already done that, it's good

Misfires can be caused by worn or fouled spark plugs - Plugs are BRAND NEW, as are wires

A weak spark (weak coil, bad spark plug wire)- Wires, coil is BRAND NEW,

loss of compression- Compression is good,

vacuum leaks- No leaks

anything that causes an unusually lean fuel mixture (lean misfire), an EGR valve that is stuck open, dirty fuel injectors, low fuel pressure, or even bad fuel.- EGR valve and regulator is brand new.

It's either the injector or the Cat.

Test the injector and backpressure of the exhaust system

Well, I've got brand new OEM injectors for the car and a new plenum gasket, so I was going to put all new injectors into it since I already have them and the injectors have 185K on them...this way if the problem is still persisting it's more than likely the Catalytic converter...it's the last thing on the list to check for a P0301 code.

I'd like to change out the injectors and plenum gasket myself, do you have any images/instructors I can use to do this? My Haynes manual doesn't help much with guidance to do this.

A code P0301 may mean that one or more of the following has happened:

Faulty spark plug or wire
Faulty coil (pack)
Faulty oxygen sensor(s)
Faulty fuel injector
Burned exhaust valve
Faulty catalytic converter(s)
Running out of fuel
Poor compression
Defective computer

Possible Solutions If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back.
If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.