hello
your TF contains a pole at 0 so it contains an integrator - any how a step input will create an output signal like a ramp - no way you can measure overshoot and setling time (like underdamped second order systems)
what kind of second order approximation are you trying to do , and why ? removing the p = 0 term is no more an approximation it's a different system ! and removing other pole(s) will not change the integrator effect either.
all your poles are real so there will be no oscillations, overshoot. For that you need complex conjugated poles.
zz = 259.6;
pp = [ 0 -1.6 -33.8];
[NUM,DEN] = zp2tf(zz,pp,1);
figure,bode(NUM,DEN)
figure,step(NUM,DEN)
figure,impulse(NUM,DEN)
