Fuel Injector Cleaner should be used every 2nd fill up of the gas tank.
So every second time you fill up the gas tank it's good to add a full bottle of fuel injector cleaner to the gas tank.
I recommend dumping the bottle of fuel injector cleaner into the gas tank and then fill the gas tank up so that the gas being added to the tank mixes with the fuel injector cleaner much better.
Too much fuel injector cleaner could cause problems and cause the engine to run rough, stall, be hard to start or run rich.
But when used properly the fuel injector cleaner should not cause any problems and should actually help clean the fuel injectors and keep the engine running good.
It's best to add a bottle of fuel injector cleaner every 2 full tanks of gasoline.
Fuel Injector cleaner is a good thing to use in moderation and it's best to use a bottle of fuel injector cleaner at least every 2 fill ups of gasoline.
However pouring too much fuel injector cleaner into your gas tank or using the fuel injector cleaner too often can cause problems with your engine valve, fuel injectors etc.
You may actually cause more harm than you do good when you use fuel injector cleaner too often.
But when used in moderation or every few months or so which is enough then you can help keep your fuel injectors as well as fuel system on your vehicle clean and free of debris.
I use fuel injector cleaner a few times per month and not more than that because it's really not needed more often than that and could cause more issues.