A geomagnetic storm model needs to take into account the coupling between magnetic field and plasma, as the storm-time field in the inner nightside magnetosphere can be very depressed compared to that of the Earth dipole, thus significantly modifying plasma transport. In this paper we extend our previous "one-way" coupling between a kinetic ring current model and a magnetospheric force-balance model to a fully magnetically self-consistent approach, in which the force-balanced fields are fed back into the kinetic model to guide its evolution. The approach is applied to simulating the 21--23 April 2001 "GEM Storm Challenge" event. We use boundary and initial conditions for the kinetic model from several spacecraft, and magnetic flux boundaries for the equilibrium code from an empirical magnetic field model. We find significant differences in the self-consistent results compared to those obtained from the kinetic model with a dipolar background field (with the same particle boundary conditions and electric fields), due mainly to changes in the particle drifts. In addition to large depressions in the nightside magnetic field values compared to a dipolar field, we also find significantly lower particle density and perpendicular plasma pressure in the inner magnetosphere in the self-consistent case, as well as local, narrow pressure peaks and strongly enhanced plasma ¿p in localized regions on the nightside.