1999 A6 Quattro Injector Replacement instructions needed
 

I have a 2.8L that has a single cylinder missing (#4). We have replaced the spark plugs, wires, and coil pack and its still persists. We run Lucas Injector Cleaner through the fuel and solves it but as soon as its out of the system, the missing comes back (we have run 6 of these Lucas cleaners and still comes back). I am looking at replacing the injector unless anyone has reason to believe it may be something else. Can anyone give me instructions on how to replace the injector if it can be done in my garage.

Thanks