Indirect sequential injection system

StarGas sequential systems are characterized by electronic management, with "Master / Slave" operation, of gas injection to power vehicles with positive-ignition engines.
The gas control unit (ECU) intercepts the opening signals of the gasoline injectors generated by the vehicle's original ECU. The microprocessor present in the gas ECU processes these data and generates the opening signals of the GAS injectors.

Some signals, transmitted by the sensors installed with the conversion kit, are used by the gas ECU calculation algorithm to improve the level of precision of the injection times.

Consequently, the gas ECU acts as a "slave" element compared to the original gasoline ECU of the vehicle ("master" element), inducing no disturbing signal at the input of the gasoline ECU, which could alter its functioning.

Thanks to this operating principle, the gas ECU ensures that only the quantity of gas strictly necessary to constitute the volume of fuel to be injected into the intake manifolds is used. This, as well as the position of the injection fittings immediately upstream of the intake valves, effectively prevents the accumulation of gas in the manifolds, avoiding any danger of bursting and the damage that would result.

While operating in gas mode, the OBD (On Board Diagnostic) of the vehicle remains active. In the event of damage to the components of the gas system affecting the emissions, the gas ECU instantly generates a signal of switching to gasoline mode and records the error. The recorded errors can then be read by the installer to formulate a correct fault diagnosis.

Forced automatic switching to petrol due to recorded errors is highlighted on the the switch.

Some versions of the gas ECU allow direct connection to the vehicle's original OBD.

The gas system turns on / off by simply pressing the switch button.
The user can perform two operations using this button, namely:

switch to gasoline
switch to gas.

The first operation allows you to change the fuel supply to the engine, from gas mode to gasoline mode. It is executed instantly by the gas ECU and involves closing the gas solenoid valves, deactivating the gas injectors, reactivating the gasoline injectors and deactivating their emulation function.

The second operation allows you to change the fuel supply to the engine, from gasoline to gas. It is carried out by the gas ECU, provided that the temperature of the engine coolant is higher than a predetermined value (switching temperature), so that the gas temperature is sufficiently hot for proper functioning of the engine and to respect the limits of polluting emissions imposed by the regulations in force. When switching, the gas ECU opens the solenoid valves, activates the gas injectors, deactivates and emulates the petrol injectors.

Consequently, during switching, the opening of the solenoid valves allows the pressurized gas to flow from the tank to the pressure reducer. In the pressure reducer, the gas pressure is lowered to the optimum value for the engine supply.
The low pressure gas leaving the pressure reducer is then sent to the gas injectors which, controlled by the gas ECU, determine the fuel dosage reaching the engine.
The entered quantity of gas, in each specific condition, is calculated by the gas ECU which, processing the injection times of the gasoline ECU, generates the commands to open the gas injectors.
The gas ECU memorizes the supply mode defined by the user with the switch.
The last power mode is kept even after the engine has stopped and it is repeated at the next start.
In any case, the engine always starts with petrol.

Indirect sequential injection (LPG or CNG)