  By using isochronous mass spectrometry (IMS) at the experimental cooler
storage ring CSRe, masses of short-lived $^{44}$Cr, $^{46}$Mn, $^{48}$Fe,
$^{50}$Co and $^{52}$Ni were measured for the first time and the precision of
the mass of $^{40}$Ti was improved by a factor of about 2. Relative precisions
of $\delta m/m=(1-2)\times$10$^{-6}$ have been achieved. Details of the
measurements and data analysis are described. The obtained masses are compared
with the Atomic-Mass Evaluation 2016 (AME$^{\prime}$16) and with theoretical
model predictions. The new mass data enable us to extract the higher order
coefficients, $d$ and $e$, of the quartic form of the isobaric multiplet mass
equation (IMME) for the $fp$-shell isospin quintets. Unexpectedly large $d$-
and $e$-values for $A=44$ quintet are found. By re-visiting the previous
experimental data on $\beta$-delayed protons from $^{44}$Cr decay, it is
suggested that the observed anomaly could be due to the misidentification of
the $T=2$, $J^\pi=0^{+}$ isobaric analog state (IAS) in $^{44}$V.
