Dear customer,
Thank you for choosing an advanced Prins VSI CNG system for your car. This system complies with strict European standards covering safety and the environment.
It is important that you read and understand this manual.
This digital manual gives you general information about CNG, and explains the Prins CNG VSI system. Scroll down further for information about the fuel selector switch, refueling CNG, fuel consumption, safety aspects, maintenance, troubleshooting, general directives and warranty terms.
Prins wishes you a lot of driving pleasure.
GENERAL INFORMATION FOR DRIVING ON COMPRESSED NATURAL GAS (CNG).
1. As the VSI CNG system starts on petrol, make sure that the fuel tank is not empty or nearly empty. This also prevents the fuel pump from running dry, which could lead to damage to the pump. The petrol in the tank should not be more than 3 months old.
2. For a guaranteed life span and optimal drivability of the VSI CNG system it is necessary to follow the prescribed maintenance. We advise a maintenance check for the VSI CNG system at an official Prins installer every 25.000 km or every 2 years. Check below to find the items for maintenance check.
3. When you smell gas in or around your car, immediately switch over to petrol and have your car checked at the nearest service point.
4. After the installation of your Prins system, you will receive a warranty certificate from your installer. This warranty certificate contains all information about your car and your Prins system. The warranty period starts on the day of conversion.
5. It is generally allowed for CNG vehicles to drive and park in an underground parking space. In some parking spaces there are restrictions imposed by the owner. The owner of the parking space may do that by placing signs at the entrance. These signs have to be respected.
CNG (Compressed Natural Gas)
Natural gas originates like petroleum, from organic material. It is extracted during the extraction of petroleum from petroleum fields and from natural gas fields. A large amount of gas is also released during the refining of crude petroleum. For the use of Natural Gas as an automotive fuel, it is compressed up to 200-250 Bar and stored in a tank hence Compressed Natural Gas. In comparison to petrol and diesel CNG is a clean fuel and its use contributes to a better global environment.
The Prins VSI CNG systeem
VSI is short for Vapour Sequential Injection. The VSI CNG system is based on the sequential injection of vaporous CNG into the engine. ‘Sequential’ means that the CNG injectors apply the CNG in a specific order or sequence which equals the injection sequence of petrol injectors. The system also allows a more precise injection of the mixture, thus complying with the tightened emission regulations. The VSI CNG system is equivalent to the original petrol injection technology and makes optimum use of the electronics already present in your vehicle. This guarantees excellent reliability.
Below you will see the different components that together form our VSI system. The main components are of OEM quality and specially developed for CNG installations. They meet the strictest regulations and certification.

- Your VSI system may differ from this diagram with some adjustments.
The CNG tank(s) is most often installed in the boot or under the vehicle. The CNG is stored under high pressure in this storage tank.
The filling point is mounted on the outside of the car or beside the fuel-filling under the fuel filler flap and is provided with a removable protective cover. This must be removed prior to refueling. A non-return valve within the filler prevents the CNG from flowing back after refueling.
There are two solenoids mounted in the system. One on the tank and one on the high-pressure line in front of the regulator (could also be mounted on the regulator). When switching back to petrol mode, switching off the ignition or in case of an error the flow of CNG will be cut off.
The manometer or a pressure sensor is placed in the high-pressure line of the VSI CNG system. The manometer or the pressure sensor is measuring the system pressure. This is an indication for the tank level.
The pressure regulator is mounted in the engine compartment. It will reduce the high tank pressure to a stable system working pressure.
The filter unit is installed between the regulator and the injector rail. The filter unit filters the pollution from the dry gas to protect the injectors. The filter unit is equipped with a pressure/temperature sensor.
The sensor measures the pressure and the temperature of the gas.
The injector rail is installed close to the inlet manifold. The injector rail contains the injectors that inject natural gas sequentially.
The temperature sensor measures the engine’s coolant temperature. The switch over time at cold engine temperature is calculated by the temperature sensor signal.