Starts and dies after battery went dead


New Member
Hi everyone, need help with issue I faced recently.
I have 1991 850i. Couple weeks ago my battery went dead and I had to jump start. Ever since, car starts and runs for 4-5 seconds and then dies. Started by checking fuel pump fuses and relays, good there. Checked fuel pumps under the seat. Next checked is fuel injectors getting power and they does, but then ECU shut them off. So far the only idea I have either factory or aftermarket (which I still didn’t find any signs of) anti theft system. Then I took batteries out to charge them. After reinstalling batteries same issue, but also it asks me to enter code on board computer. I found in owners manual page about code as an anti theft protection, but I’m not sure if in my case it’s just for the board computer or engine as well, also I’m not sure where I can get that code