Systems Flashcards
7 cards from real CNG practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Systems flashcards as text
What does an automatic vehicle fuel shutoff valve (AVFS) do in the event of a significant collision?
Answer: Shuts off CNG flow from cylinders automatically upon impact
An AVFS is an inertia- or signal-activated valve that closes automatically during a collision to stop CNG from flowing out of the tank.
A CNG vehicle experiences hard starting in very cold weather despite a full tank. Which system issue is most likely?
Answer: Regulator freeze-up due to moisture in the fuel
Moisture in CNG can freeze inside the regulator at low temperatures, restricting or blocking gas flow and causing hard starting.
What is the role of the electronic control module (ECM) in managing a dedicated CNG fuel system?
Answer: Controls injector timing, duration, and stoichiometry for optimal combustion
The ECM uses sensor data to calculate and control injector timing and pulse width, keeping the air-fuel mixture at the optimal stoichiometric ratio.
When inspecting CNG cylinders, which condition requires the cylinder to be immediately removed from service?
Answer: Visible cracks, bulges, or deep gouges in the cylinder wall
Cracks, bulges, or deep gouges compromise cylinder structural integrity and are mandatory grounds for immediate removal from service per NGV2 standards.
What is the typical service life of a Type 4 (all-composite) CNG cylinder used on a light-duty vehicle?
Answer: 20–25 years
Type 4 cylinders are generally certified for 20 to 25 years of service life, after which they must be removed from service regardless of visual condition.
Why must CNG cylinders be hydrostatically tested during their service life?
Answer: To verify structural integrity under pressure greater than normal operating pressure
Hydrostatic testing fills the cylinder with water and pressurizes it above normal operating pressure to detect weaknesses or deformation without the risk of gas ignition.
On a CNG vehicle with a sequential multi-port injection system, what advantage does it offer over a single-point mixer system?
Answer: More precise fuel delivery per cylinder improves power and emissions
Sequential multi-port injection delivers CNG directly to each cylinder's intake port, providing more precise metering and better power output with lower emissions.