CNG Maintenance and Troubleshooting 2

Question 1

Which solution is the approved method for field-testing CNG fuel line fittings for leaks?

Accepted Answer

Soapy water or approved leak detection solution

Answer

Approved leak detection fluid (soapy water or commercial solution) is applied to fittings; bubbles indicate a leak without ignition risk.

Question 2

A CNG vehicle's high-pressure regulator is suspected of failing. Which symptom most directly points to a regulator malfunction?

Accepted Answer

Consistently low fuel pressure delivered to the engine

Answer

A failing high-pressure regulator cannot step down tank pressure correctly, resulting in consistently low delivery pressure to the engine.

Question 3

When inspecting CNG high-pressure cylinders, what condition requires the cylinder to be immediately removed from service?

Accepted Answer

Any visible crack, gouge, or deep abrasion on the cylinder

Answer

Any crack, gouge, or deep abrasion compromises cylinder structural integrity and mandates immediate removal from service per NFPA 52 and NGV2 standards.

Question 4

After replacing a CNG fuel filter, what must be done before returning the vehicle to service?

Accepted Answer

Perform a full leak test on all disturbed connections

Answer

Any time a fuel system component is opened and reassembled, a leak test on all disturbed fittings and connections is mandatory before returning to service.

Question 5

A CNG technician notices the pressure relief device (PRD) has vented. What is the correct first diagnostic step?

Accepted Answer

Check if the vehicle was exposed to an external heat source or fire

Answer

PRD venting is a safety event; the technician must determine if excessive heat or fire caused the activation before replacing the device.

(CNG) Compressed Natural Gas Practice Test

(CNG) Compressed Natural Gas Practice Test

CNG Maintenance and Troubleshooting 2