Engine control unit destroyed during start-up

Hello, I have a Passat 35i, manufactured in 1990, with a 1.8l PF engine and a manual transmission. Recently, to my surprise, the engine suddenly stopped starting. An inspection revealed that the fuel injection valves are completely connected to ground, and the engine is completely dead. A used engine control unit (ECU) initially made the engine run again. However, after 4 days, the same problem occurred again. Now I have installed the third ECU, and I am constantly worried that it will be destroyed again. An electrical inspection of the fuel injection system did not reveal any errors. The ground points are in order, and the regulator voltage is OK. Perhaps someone has already experienced this problem and can give me a tip. By the way, the engine was running perfectly. The control unit will definitely be destroyed when the engine starts.
Best regards, Peter