What is a likely cause for a diesel engine to run rough and stall?

A diesel engine may run rough and stall due to air in the fuel system because air can disrupt the consistent flow of fuel needed for proper combustion. Diesel engines rely on a precise mixture of fuel and air for efficient operation; any introduction of air can lead to incomplete combustion, resulting in rough running. If enough air enters the fuel system, it can cause significant performance issues, including stalling, as the engine struggles to maintain the necessary power output. This condition can be exacerbated by issues such as leaks in the fuel lines or faulty connections that allow air to infiltrate the system.

When diagnosing engine performance problems, it's essential to consider the integrity of the fuel system. If air is present, it can lead to a loss of fuel pressure and inadequate fuel delivery to the injectors, further contributing to rough running and stalling.

In contrast, while poor fuel quality, a plugged return line, and low transfer pump pressure can also lead to engine performance issues, the specific effect of air in the fuel system directly impacts combustion efficacy and stability, making it a primary concern when experiencing rough operation and stalling in diesel engines.