This article reviews the decay studies of neutron-deficient nuclei within the mass region A = 56-100 performed at the Ion-Guide Isotope Separator On-Line (IGISOL) facility in the University of Jyväskylä over last 25 years. Development from He-jet measurements to on-line mass spectrometry, and eventually to atomic mass measurements and post-trap spectroscopy at IGISOL, has yielded studies of around 100 neutron-deficient nuclei over the years. The studies form a solid foundation to astrophysical rp-process path modelling. The focus is on isomers studied either via spectroscopy or via Penning-trap mass measurements. The review is complemented with recent results on the ground and isomeric states of ⁹⁰Tc. The excitation energy of the low-spin isomer in ⁹⁰Tc has been measured as E_x = 144.1(17) keV with JYFLTRAP double Penning trap and the ground state of ⁹⁰Tc has been confirmed to be the (8⁺) state with a half-life of T_1/2 = 49.2(4) s. Finally, the mass-excess results for the spin-gap isomers ⁵³Co^m and ⁹⁵Pd^m and implications from the JYFLTRAP mass measurements for the (21⁺) isomer in ⁹⁴Ag are discussed.