A Sequential CNG Kit works the same way. It has a separate CNG gas ECM and multiple CNG Gas Injectors to control the flow and quantity of the CNG gas.
These are installed just next to the petrol injectors on the engine cylinder head. The quantity of the CNG Gas is also monitored by the Vacuum Pipes installed.
The Difference between a Sequential CNG Kit & Conventional CNG Kit is as same that of a Petrol Carburetor Car and MPFI Car. In MPFI cars the delivery and quantity of fuel are controlled by the Petrol Injectors installed in the Cylinder Head Assy. The Injectors are connected with the Electronic Control Module (ECM) of the Car which takes signals from other sensors fitted and helps in improving the pick and mileage of the cars and helps in reduction of pollutants levels also.