There is a injector cleaner that is not a simple pour in. I use it on my vehicles and it is NOT a simple process.
Napa and some others carry this cleaner. It requires a hose kit to hook up to the fuel rail. You have to pinch off the return fuel line, disconnect the fuel pump (via fuse) and the engine runs off this mixture. When pressure drops in can, the engine will die. There is the "jist" of the procedure.
The last time I used the cleaner was on my 90 f150 w/ 302. After using the cleaner, the engine would run on a fuel pressure about 10 pounds less. It is well worth it.
Ask each, the mechanic, the dealer, or where you have the oil changed if this is the procedure they use.