1999 Chevy Malibu Injectors

First, I would recommend a fuel injector cleaner that mixes with your fuel. You can get it at any parts store.

As far as testing them, you need what is called a noid light to see if they are getting power. THe light in the noid will pulse when the injector should be delivering fuel to the cylender.

Are you having a problem with a specific cylender? What does the spark plug look like?