Natural Gas (NG) Vehicle Module

The natural gas (NG) vehicle module (Fig 1) provides two functions. The first function operates the fuel injectors and is referred to as the injector driver module (IDM). The second function sends a fuel level indicator signal to drive the fuel gauge and is called the fuel indicator module (FIM). IDM NG vehicle fuel indicator driver signals are based on powertrain control module (PCM) fuel injector driver signals and are controlled directly by the corresponding injector drivers in the PCM. The IDM must be used to provide the NG fuel injectors with the required high current necessary for proper operation. The greater demand of NG fuel injector current warrants an increased size of the injector driver and increased heat dissipation. Given these conditions, the PCM would not be suitable for placement of these drivers. The IDM closely resembles the Electronic Engine Control 60 Pin PCM module in appearance. This style of module is used on the NG F-Series and Crown Victoria, while a 90 pin Alternative Fuel Control Module (AFCM) (Fig 2) is used on the E-Series.

The IDM injector drivers are capable of controlling the amount of current flow to each NG fuel injector. Once the fuel injector is open, the IDM NG fuel injector driver will reduce current flow sufficient to continue to hold the fuel injector open. This is done by the IDM in an effort to reduce heat. If the IDM driver does not detect the required peak current to initially open the NG fuel injector within a specified amount of time, the IDM driver will drop current to fuel injector hold open current.

The fuel indicator module (FIM) is not part of the powertrain control subsystem and will not be discussed here.