Nodal analysis Example
You need another independent equation. Try writing a KCL equation at node 1 that relates \$i_\Delta\$ to the currents through the \$10\Omega\$ and \$30\Omega\$ resistors. Don't change your existing equation, just write a new one. You should be able to do the same substitutions for \$v_1\$ and \$v_3\$ so that you end up with a second equation with only \$i_\Delta\$ and \$v_2\$ as unknowns.

Hopefully, your two equations are independent and can be solved for both unknowns.