Speed Density

SPEED DENSITY SYSTEM
Data Inputs
Three specific data sensors provide the Powertrain Control Module (PCM) with the basic information for fuel management portion of its operation. These signals to the PCM establish the engine speed and air density factors.

Engine Speed Signal
The engine speed signal comes from the distributor low resolution circuit. The PCM uses this information to determine engine speed (RPM).

Air Density Calculation
Air density is derived from Intake Air Temperature (IAT) and Manifold Absolute Pressure (MAP) sensor inputs. The IAT sensor measures the air temperature that is entering the engine. The IAT signal works in conjunction with the MAP sensor to determine air density. As the intake manifold pressure increases, the air density in the intake manifold also increases and additional fuel is required.

INJECTOR PULSE WIDTH
This information from the IAT and MAP sensors is used by the PCM to control injector pulse width.

SPEED DENSITY BACKUP FUNCTION
The speed density system is only needed when there is a Mass Air Flow (MAF) sensor malfunction. If the PCM detects a malfunction with the MAF sensor circuit, the PCM will default to speed density fuel management.