not bad, you have to remove the upper intake. That involves disconnecting the EGR tube from the exhaust manifold, disconnecting all vacuum lines, throttle cable assembly where it connects to butterfly valve, coolant hoses going to the upper intake, ignition coils and wires and air intake ducting. You will need a 1 & 1/16" wrench for the egr fitting, and there are 8 bolts on the upper intake, the one in the passenger back is kind of hard to find and access. You will also need to disconnect all the electrical connections (DPFE sensor, MAP sensor, MAF sensor, TPS sensor). Once you get the upper intake off, you can "pop" out the injectors from the lower intake and remove them from the fuel manifold and replace.
To me, the most difficult parts of this are the removing and the reseating of the upper intake manifold and getting the tubing / hose that connects to the PCV unrouted and rerouted in the right place. Also, if the EGR tubing fitting to the exhaust manifold has never been disconnected prior, it may be tough to remove. You also have to put the most rear driver's side bolt in the manifold first as the firewall will not let you drop it in if the manifold is in the right location. I put some tape under the bolt head so the bolt does not protrude at the bottom and then remove the tape the let the bolt drop into its threaded hole once I get the manifold seated.
Just curious, why are you replacing the injectors. If you are looking for gas mileage improvement you may get some but, it would not be worth it (cost of the injectors and time) to me to do this unless I was sure one or more of the injectors was not working. I mean you should be getting about 18-20 MPG on the highway at 65 mph and in town driving you can get as low as 13-15 MPG.
