We performed high-precision mass measurements of the proton-rich nuclei 52Ni and 51Co with the LEBIT Penning trap at the Facility for Rare Isotope Beams (FRIB). For 52Ni, a mass excess of -22474.8(2.2) keV was determined, which is consistent with a recent storage-ring measurement at the Cooler-Storage Ring (CSRe) but has a factor 37 improved precision. For 51Co, we obtained a mass excess of -27375.1(5.7) keV, agreeing with a recent CSRe result, while reducing the uncertainty by a factor 2. Combining our mass value for 52Ni with the known two-proton decay energy of 54Zn, we determined the mass excess of 54Zn to be -6463(42) keV. These new mass values reveal a substantial breakdown of the isobaric mass multiplet equation for A = 52 and A = 54, and provide stringent benchmarks for isospin-symmetry-breaking effects in the proton-rich fp-shell, favoring theoretical descriptions that omit the Coulomb-exchange term.