The generator matrix

 1  0  1  1  1  1  1  1  1  0  1  1  1  0  1  1  X  1  1  1  1  1  1  1  X  1  1  1  1  1 aX  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  0 (a+1)X aX  0  X  X aX  1  X  1
 0  1  1  a (a+1)X+a+1  0 (a+1)X+1  a (a+1)X+a+1  1  0  a (a+1)X+1  1 (a+1)X+a+1 X+a  1  X (a+1)X+1 aX+a+1 X+a  X  1 aX+a+1  1  X aX+1 a+1  0 X+a  1 aX+1  a aX+a+1  X (a+1)X+a aX+a+1 aX (a+1)X+a+1 a+1  a a+1 a+1 aX+a+1  X (a+1)X+a X+a+1 aX aX+a (a+1)X+1 (a+1)X+a+1 (a+1)X+a (a+1)X+a (a+1)X+a X+a a+1 X+a aX+1 X+1 (a+1)X+1 aX+1 aX+1  1  1  1  0  0  X  0  X aX aX aX (a+1)X  1  1  1  1  1  1  1 (a+1)X  1 (a+1)X
 0  0 (a+1)X  0  X  X (a+1)X  X (a+1)X  X  0  0  X  X  0 (a+1)X aX aX  0 (a+1)X aX (a+1)X aX aX (a+1)X  X  X  0 (a+1)X  X (a+1)X (a+1)X  X  0  X  0 (a+1)X  0 (a+1)X  X (a+1)X  X aX aX aX aX  0 (a+1)X (a+1)X  0  X  0 (a+1)X aX aX aX  X aX (a+1)X  X  X aX  0 aX  0 aX  X  0 (a+1)X aX aX aX (a+1)X  0  0 aX  0 aX (a+1)X  X aX (a+1)X  X  0
 0  0  0  X aX  X aX (a+1)X (a+1)X  0  X (a+1)X  0 aX aX (a+1)X  0  X  0 aX (a+1)X  X  0 aX  0  0 aX (a+1)X  0  X aX (a+1)X aX  X (a+1)X aX  X (a+1)X  0  0 aX  X  X  0 (a+1)X aX  0 (a+1)X  X aX (a+1)X  0  0  X  0 (a+1)X  0 aX  X  X (a+1)X  X (a+1)X (a+1)X  X  0 aX aX aX aX  0  X  X  0  X  X (a+1)X aX (a+1)X  X (a+1)X (a+1)X (a+1)X (a+1)X

generates a code of length 84 over F4[X,sigma]/(X^2) who´s minimum homogenous weight is 246.

Homogenous weight enumerator: w(x)=1x^0+672x^246+1830x^248+264x^250+72x^252+228x^254+42x^256+24x^260+312x^262+579x^264+24x^266+36x^270+9x^272+3x^280

The gray image is a linear code over GF(4) with n=336, k=6 and d=246.
This code was found by Heurico 1.16 in 9.52 seconds.