The Mercedes-Benz Actros 1840 uses a V8 engine, but pinpointing the exact firing order without knowing the specific engine code (e.g., OM460LA) is impossible. Mercedes-Benz uses various V8 engines across different Actros models and years, each with its own unique firing order.
To find the firing order, you need to locate the engine's data plate. This plate, usually on the engine block itself, will contain the engine code. With that code, you can then consult a Mercedes-Benz service manual or an online database specific to commercial vehicle engines.
