What will cause a diesel engine to run rough and stall?

What will cause a diesel engine to run rough and stall?

• A. Poor fuel quality.
• B. A plugged return line.
• C. Air in the fuel system.
• D. Low transfer pump pressure.

Answer: (C)

Air in the fuel system prevents proper fuel delivery in a diesel engine, which leads to rough running and stalling. Diesel injectors rely on a continuous, air-free column of fuel being supplied at high pressure. When air is trapped in the lines, the pump has to compress and move air before it can push fuel to the injectors, causing interruptions in fuel delivery. Those interruptions result in incomplete combustion, cylinder misfires, and the engine can stumble and eventually stall if the air isn’t purged. Poor fuel quality can cause roughness or power loss due to contaminants or degraded cetane, but the symptoms aren’t as directly tied to immediate loss of fuel continuity as air in the system. A plugged return line and low transfer pump pressure can cause abnormal pressure and performance issues, but they usually don’t produce the specific combination of rough running followed by stalling caused by air pockets in the fuel path.

Air in the fuel system prevents proper fuel delivery in a diesel engine, which leads to rough running and stalling. Diesel injectors rely on a continuous, air-free column of fuel being supplied at high pressure. When air is trapped in the lines, the pump has to compress and move air before it can push fuel to the injectors, causing interruptions in fuel delivery. Those interruptions result in incomplete combustion, cylinder misfires, and the engine can stumble and eventually stall if the air isn’t purged.

Poor fuel quality can cause roughness or power loss due to contaminants or degraded cetane, but the symptoms aren’t as directly tied to immediate loss of fuel continuity as air in the system. A plugged return line and low transfer pump pressure can cause abnormal pressure and performance issues, but they usually don’t produce the specific combination of rough running followed by stalling caused by air pockets in the fuel path.