Do diesel engine produce vacuum when running?

No, diesel engines do not produce vacuum when they are running. In fact, they actually produce a slight positive pressure in the intake manifold. This is because the diesel engine's intake stroke is not as effective as the gasoline engine's intake stroke. The diesel engine's piston does not move as far down the cylinder, so it does not create as much suction. As a result, the air/fuel mixture in the diesel engine is not as dense as the air/fuel mixture in the gasoline engine. This less dense mixture requires less pressure to enter the cylinder, so the diesel engine produces a slight positive pressure in the intake manifold.