as i remember the injectors 1-4 and 2-3 are in pair, as the coil pack is too
but i also have two service Y cables, if the injector output is faulty to run the 4 injector from one single output only in batch
a capacitor was wrong and the injector closed slowly, overfuelled the 2nd -3rd cylinders,and the 2-3 cylinder's sparkplugs were full black from coal, and they don't made sparks, run only with two cylinders, 1-4 was OK
so the 1st cylinder injector connector was "paired" with 2nd, and 4th with the 3rd, in the box 1-4 is in pair (maybe for me only, but this worked me as fail-safe)