crazy 89 gmc

[walterbolton]

i got out of the gas engine industry around 1990 and went into heavy diesel repair so i am a little rusty on gas engine diagnostics. my dad brought me his truck to try and fix and i have come to the conclusion that its possessed
TRUCK DETAILS
1989 gmc 1500 sierra (strip model but not w/t)
reg cab long bed
4.3 tbi automatic two wheel drive
bone stock-no mods what so ever except for the ugly wheel covers he put on it
WHAT IT IS DOING
he told me it was running bad and cutting out but when he got it to me it was running fine, i drove it down the road and noticed no problems. he put a new fuel filter on it so i checked that it wasn't installed backwards-it was ok, new plugs and wires (not auto zone crap) also new cap and rotor. it all looked good to me and was running fine, thinking that maybe he got some bad gas i told him to drive it. as he started backing out it died. started right back up but was running bad, pulled it back in and it died again, this time i heard a clicking noise in the engine compartment, he informed me that it was the injectors spraying? i pulled the air cleaner and sure enough the injectors were still pulsing even with the key off and erratically absolutely no pattern some times 7-8 seconds and as fast as a quick shot. i tried to hook up my otc scanner from the old days to check if any codes were present and try to see the engine management details. i can not communicate with the ecm. this was i also noticed that every time the injectors pulsed the check engine light would come on. i dug around in my box and found my old aldl key and tried to do the old blink code trick with no luck.
so i started checking all the grounds, relays, fuses all checked good. i think it might be an ecm problem but not sure, also the temp does not seem to be a factor as it will do it cold or hot. any one else ran into this problem? what am i missing? thanks in advance