Engine stalling, sometimes called “choking” in machinery, is a common issue in modern engine operation. Owners worry when their machines behave poorly—losing power or running erratically—but sometimes the problem is misdiagnosed. Here is a summary of practical guidance (from experience, not formal theory) on how to detect engine stalling.

I. Understanding Engine Idle, High Idle, and Rated Speed

1. Idling (idle speed)

   • All engines, including vehicle engines, have an idle speed, defined as the engine running with no load.

   • “High idle” and “low idle” are distinctions; there is no concept of “stationary speed” outside idle.

2. Rated speed

   • This is the maximum engine speed under standard load.

   • The ratio between high idle and rated speed is called the governor range.

   • The ratio between actual engine speed and the rated speed determines whether the engine is stalling (choking).

3. Typical tolerance

   • Normally, engines have 10–15% allowable “speed loss” under normal operation.

   • For example, an engine with high idle 1980 rpm and rated speed 1800 rpm has a standard governor range of 10%.

     • If under full throttle the engine reaches at least 1750 rpm, it is considered normal.

     • If engine speed falls below this, it may indicate stalling.

II. Special Cases in Engine Design

• Some brands maintain high idle equal to rated speed using software control.

  • This prevents the engine from stalling at low throttle, but reduces machine operational speed as a hidden trade-off.

• Original equipment manufacturers (OEMs) usually test engines at full throttle and rated power, not partial load, which is why low-throttle operation is discouraged—especially in turbocharged engines.

  • At low throttle, turbochargers do not operate; only mechanical superchargers could function.

III. Determining Engine Stalling (“Choking”)

1. Measure maximum throttle speed

   • Use the engine data plate to check high idle and rated speeds.

   • If the engine cannot achieve the expected rpm under full throttle, it may be stalling.

2. Compare performance under load

   • Engines under load that fail to reach rated speed, or show hesitation/rough operation, are likely experiencing choking.

3. Look for patterns

   • A normal engine exhibits about 10–15% speed drop under varying load.

   • Anything beyond this range may indicate a fuel delivery or injection system problem.

IV. Common Causes

• Almost all engine stalling issues—traditional diesel or electronically controlled—are caused by fuel system problems.

• Symptoms may include: reduced acceleration, black smoke, or engine sputtering under load.

Summary:

• To detect engine stalling, compare actual engine speed under load and full throttle with rated specifications.

• Understand idle, high idle, and rated speeds to determine if the engine is “choking.”

• Most stalling problems in construction machinery engines are fuel system-related.