code 21 issues

Hey guys think first time post from Australia, have a hair pulling issue with my car 1986 turbo z manual, plugged in nistune 2 days ago and managed to start the car running rich, pulled the ecu apart and found the maf mod had already been done so I re calibrated the tune to suit an n60 maf, all fine and good. Then I got code 21 which I assumed was a bad PTU so I replaced it with my spare donor car PTU, started and was fine again, then the next day had the same issue code 21 popped up again and would not start, so I loosened the dizzy adjuster screw and turned the dizzy to activate fuel and spark, funny thing is the car still had spark and fuel but still wont start, any ideas? might to pwr-2 mod and see if that changes anything.
If it had no spark I would be looking into ignition relays, and fusible links, I checked the voltage on my coil plug and had 12v constant and during spark signal?