This did in fact happen to me once. Mine was right bank.
It was fuse block related..there are 2 fuses for the injectors (INJ1 and INJ2 i think).
mine had a add-on circuit on one of these, that apparently had flexed the fuse connection tabs a little too far. When the circuit was removed from that fuse, there wasn't enough pressure being applied to the legs of the fuse to make contact. Basically the add-on circuit flexed the fuse holder contacts and yielded them..reducing the contact force on the legs. Fuse would pull out without much resistance.
I ended up sticking a very small flat head screw driver in there and bending the contacts back together one-by-one. The fuse then went back in tightly, and problem hasn't been back since.
Start by checking those INJ fuses and wiggle to see if they are tight. If not them...maybe pinched wiring somewhere to that bank ?
Here's a bit of what I'm into:
Short & Long Blocks - build to order
Basic rebuilds to Darton sleeved strokers
GTO rear end parts and rebuilds
Dana Gearsets (OEM Australian)
OEM seals, crush sleeves, pinion nuts, ring gear bolts, pinion shims.
specials on 3.73 and 3.91 gearsets now