Which system uses engine vacuum signals to meter fuel, typically in older vehicles?

Which system uses engine vacuum signals to meter fuel, typically in older vehicles?

• A. Direct injection
• B. Vacuum-assisted metering systems
• C. Electronic port injection
• D. Diesel injection

Answer: (B)

In older engines, fuel delivery was often controlled by engine vacuum signals rather than electronics. A vacuum-assisted metering system uses the intake manifold vacuum as the signal to adjust how much fuel flows. A diaphragm or metering chamber responds to the varying vacuum produced by the engine load and throttle position, moving a valve or rod to regulate fuel accordingly. When throttle is light and vacuum is high, the system limits fuel; when throttle opens and vacuum drops, more fuel is allowed through. This direct, mechanical linkage between the engine’s breathing and fuel delivery was common before electronic control systems became standard. Direct injection places fuel directly into the cylinders and is governed by electronic controls. Electronic port injection uses electronic control to meter fuel at the intake ports. Diesel injection relies on compression-ignition metering, not on intake-manifold vacuum signals.

In older engines, fuel delivery was often controlled by engine vacuum signals rather than electronics. A vacuum-assisted metering system uses the intake manifold vacuum as the signal to adjust how much fuel flows. A diaphragm or metering chamber responds to the varying vacuum produced by the engine load and throttle position, moving a valve or rod to regulate fuel accordingly. When throttle is light and vacuum is high, the system limits fuel; when throttle opens and vacuum drops, more fuel is allowed through. This direct, mechanical linkage between the engine’s breathing and fuel delivery was common before electronic control systems became standard.

Direct injection places fuel directly into the cylinders and is governed by electronic controls. Electronic port injection uses electronic control to meter fuel at the intake ports. Diesel injection relies on compression-ignition metering, not on intake-manifold vacuum signals.