The ubiquity of gasoline direct injection (GDI) vehicles has been rapidly increasing across the globe due to the increasing demand for fuel efficient vehicles. GDI technology offers many advantages over conventional port fuel injection (PFI) engines, such as improvements in fuel economy and higher engine power density; however, GDI technology presents unique challenges as well. GDI engines can be more susceptible to fuel injector deposits and have higher particulate emissions relative to PFI engines due to the placement of the injector inside the combustion chamber. Thus, the need for reliable test protocols to develop next generation additives to improve GDI vehicle performance is paramount. This work discloses a general test method for consistently fouling injectors in GDI vehicles and engines that can accommodate multiple vehicle/engine types, injector designs, and drive cycles, which allows for development of effective GDI fuel additives. A key factor to the versatility of this test protocol is the test fuel formulation, which uses added chemical accelerants to mimic the fouling effects of fuel aging and sulfur accumulation in the injector nozzle. The test fuel formulation serves to accelerate the fouling potential of fuels that are already capable of dirtying-up fuel injectors on their own without chemical accelerants and allows real-world fuels to be evaluated for fuel additive performance within more reasonable test times. This test method was also complimented by emissions and fuel economy measurements in order to quantify the negative effects of injector fouling on vehicle performance and the opportunity for DCAs to help prevent these problems.