Several strong narrowband resonances are observed in the transmission spectra of fiber Bragg gratings photo-written in photonic crystal fiber that has a refractive index-neutral germanium/fluorine co-doped core. Experimental results for the strain, temperature and refractive index sensitivities of these mode resonances are reported and compared to those of conventional single mode fiber. In particular, we identify three kinds of resonances whose relative sensitivities to strain, temperature and refractive index are markedly different and present numerical simulations to explain these properties. Potential multiparameter optical sensor applications of these mode resonances are briefly discussed.