What ECM? They're mechanically injected diesels. The main purpose of the electrical system is to run the starter to crank the engine. And maybe headlights and stuff.
They're very simple cars.
Yep to parent poster look at the fascinating mechanical fuel pumps in some detail they are incredible machines in their own right
Direct injected gasoline engines have a high pressure fuel pump (in addition to the electrical low pressure) mechanically powered by the crank
My Diesel has an analog glow plug controller. That's literally the most complicated electronics in the whole car.