Final answer:
The most likely cause of excessive black smoke from a diesel engine when started in the morning is a bad fuel injection nozzle. Other potential causes include a restricted fuel filter and a leaking fuel return line.
Step-by-step explanation:
Excessive black smoke from a diesel engine when started in the morning can be caused by several factors. From the given options, the most likely cause would be a bad fuel injection nozzle.
A bad fuel injection nozzle can lead to incomplete combustion of fuel, resulting in the production of excess black smoke. This can occur when the nozzle is clogged or damaged, causing fuel to spray poorly or in an incorrect pattern.
Other factors that can also contribute to excessive black smoke include a restricted fuel filter and a leaking fuel return line. A restricted fuel filter can cause inadequate fuel flow, leading to improper combustion and increased smoke. A leaking fuel return line can result in the recirculation of unburned fuel, causing black smoke.