CNG - Compressed Natural Gas Vehicle Conversion and Installation Questions and Answers

Question 1

A technician is installing a CNG fuel system on a vehicle. According to NFPA 52, what is the minimum required clearance between a CNG fuel line and the engine exhaust system?

Accepted Answer

6 inches (150 mm)

Answer

1 inch (25 mm)

Answer

3 inches (75 mm)

Answer

9 inches (225 mm)

Question 2

When installing CNG cylinder mounting brackets to a vehicle's frame, which of the following is a critical requirement to prevent premature cylinder failure?

Accepted Answer

Ensuring a rubber or other non-metallic isolating material is placed between the cylinder and the metal brackets.

Answer

Welding the brackets directly to the frame for maximum strength.

Answer

Using grade 5 bolts torqued to the highest possible specification.

Answer

Applying a thick layer of paint to the brackets and cylinder contact points to prevent corrosion.

Question 3

A vehicle is being converted to a bi-fuel CNG system. After the hardware installation, the Engine Control Unit (ECU) must be calibrated. What is the primary goal of adjusting fuel trims during the CNG calibration process?

Accepted Answer

To match the long-term and short-term fuel trims on CNG as closely as possible to the values when running on gasoline.

Answer

To maximize engine horsepower on CNG.

Answer

To ensure the vehicle's diagnostic trouble codes are suppressed.

Answer

To decrease the fuel rail pressure to its lowest possible setting for efficiency.

Question 4

Which of the following labels is required by the EPA to be affixed in the engine compartment of a vehicle that has been converted to operate on CNG?

Accepted Answer

A label with the name and address of the conversion system manufacturer and a statement that the vehicle complies with EPA regulations.

Answer

A label indicating the cylinder's last hydrostatic test date.

Answer

A label showing the vehicle's new, lower weight capacity.

Answer

A diagram of the CNG fuel flow and a list of all installed components.

Question 5

During a CNG conversion, a technician must route the high-pressure fuel line from the cylinders in the trunk to the engine bay. According to NFPA 52 guidelines, where should the fuel line be routed?

Accepted Answer

Attached securely to the exterior of the vehicle's frame or body.

Answer

Through the passenger compartment for easy inspection access.

Answer

Inside the main frame rail for maximum protection.

Answer

Directly adjacent to the vehicle's battery cables for efficient routing.

Question 6

A customer wants to convert their 2-year-old light-duty truck to CNG. According to EPA regulations for converting 'new and relatively new vehicles,' what is required for the conversion system?

Accepted Answer

An EPA-issued Certificate of Conformity for that specific vehicle/engine group.

Answer

A letter from the original vehicle manufacturer approving the conversion.

Answer

A simple declaration from the installer that the system meets emissions standards.

Answer

Proof that the vehicle has been driven at least 50,000 miles before conversion.