An experimental study was carried out to characterize the spray atomization process of automotive port fuel injectors retrofitted to a novel pressure modulation piezoelectric driver, which generates a pressure perturbation inside the fuel line. Unlike many other piezoelectric atomizers, this unit does not drive the nozzle directly. It has a small size and can be installed easily between regular port injector and fuel lines. There is no extra control difficulty with this system since the fuel injection rate and injection timing are controlled by the original fuel-metering valve. The global spray structures were characterized using the planar laser Mie scattering (PLMS) technique and the spray atomization processes were quantified using phase Doppler anemometry (PDA) technique. Four standard gasoline port injectors including central port injection (CPI), electrostatic-discharge-machined (EDM) director-plate, compound silicon-micro-mach-ined (SMM) and dual-stream (DS) injectors were tested in this study. The experimental results showed that this pressure modulation technique can greatly enhance the spray atomization process of the gasoline port injectors. The spray behavior showed a strong dependence on the driving frequency and power of the pressure modulator. The optimal operating conditions for the pressure modulation device, however, depend on the injector design.