Diesel engines, particularly those in semi-trucks, have their own unique set of problems. While their engines are similar to those in passenger vehicles that have diesel engines, the engines inside these commercial trucks are much larger, require more power, and eat up more fuel and lubricants. On top of that, they can have any number of other issues. Some of those common issues and how they are fixed are as follows. 

Malfunctioning Glow Plugs

A glow plug is like a spark plug, except that instead of creating a spark to ignite fuel, the glow plug slowly warms up like a heating coil in a toaster. A malfunctioning glow plug in a diesel engine will not be able to ignite the fuel and provide power to the diesel engine. When a truck of this size cannot get started or has a hard time starting, the first thing a truck repair technician checks is the glow plug. He/she replaces the glow plug and then attempts to start the truck to see if that is the problem. 

Contaminated Diesel Fuel

Diesel fuel, as you are probably aware, is very thick. It looks like a watery engine oil going into the tank. It is more viscous than standard gasoline and less viscous than water itself. Because it is heavier, denser, and a little more "sticky," a lot more contaminants can end up in the fuel from time to time. Your truck repair technician will sample the fuel by drawing a little out of the tank and checking it. If there appears to be anything out of the ordinary with the fuel, the whole tank has to be emptied and flushed. Then new fuel can be put into the tank and the truck started. The truck will need to run for some time so that the clean fuel gets a chance to make it through the engine a few times and hopefully clear out any residue from the contaminated fuel. 

Black Exhaust

While diesel trucks generally pump out a lot more dirty smoke because they are essentially burning fuel into particulates, your truck's exhaust smoke should not resemble gaseous tar. Several parts inside the truck can contribute to the black exhaust. Your technician has to take the truck apart to examine each of these possible parts in turn to find what is causing the problem. Replacing the parts at fault will correct this common truck issue.