What is density compensation in engine fuel metering intended to do?

• A. The ECU adjusts flow and rail pressure to maintain constant mass flow when density changes.
• B. The ECU ignores density and maintains constant volume.
• C. Density compensation increases fuel temperature.
• D. Density compensation lowers engine compression.

Answer: (A)

Density compensation is about keeping the fuel mass entering the engine constant as fuel density changes. Fuel density varies with temperature and pressure, so the same injector pulse and rail pressure would deliver different masses if density shifts. The ECU compensates by adjusting both how much fuel is injected (flow via injector timing) and the rail pressure to maintain a constant mass flow per cycle, preserving the intended air-fuel ratio. If density goes up, the system reduces the injected mass; if density goes down, it can increase it to keep the mass steady. Ignoring density or sticking to a constant volume would change the actual fuel mass delivered, throwing off fueling. Increasing fuel temperature or altering engine compression aren’t how this compensation is achieved in metering.