1999 Grand Am stalled, strong gas smell

It could be a lot of things - except fuel filter. Sounds like it threw a rod.

White smoke can sometimes be coolant in the cylinder/s. These cars have a notorious problem with intake exhaust gasket failure. Are you losing coolant?

mechanic came to my house and checked it out and the number 4 fuel injector stays open and wont shut off. its a continuous spray. he said it needs a new computer. he checked the injectors with a test light and the number 4 injector was the only one that the light lit up wen he connected it to the power and ground side. and its only supposed to light on one. he says a new comp would solve it, do yall think so?

The computer grounds each injector, to make it spray fuel. A shorted wire, bad injector, or bad computer, will cause a constant spray.

Without a far better decription of exactly how he set-up his equipment I can't agree or argue with his diagnosis. GW