91 blazer can not diagnose?

ok so heres the prob, have my blazer , and its been running like crap, feels like its not gettin enough gas, its bucking and backfiring and popping and not wanting to go, smells like gas, have had the fuel filter changed many of times a quick fix becuz it would act better after doing so, not anymore.. now the engine light comes on , so i brought it to the mechanic, he says its getttin 2 much gas, ok so he says its either a module in the computer or its the fuel pump in the tank., i replaced the computer , that didnt help-, ok heres the thing, when the air filter was off , and they reved the engine i saw fire shoot out of the fuel ingection.. ok so heres the question , do ya think its the fuel pump or the timing??