FREE CNG Engines and Fuels Questions and Answers

Question 1

A transit bus's engine compartment makes a puffing noise during operation. Which one of the following might be the cause?

Accepted Answer

The exhaust manifold gasket is leaking.

Answer

The air intake is leaking.

Answer

The water pump is faulty.

Answer

It’s just a normal noise when operating.

Question 2

After three hours, a 350-mile typical range CNG transit bus stops running. 375 psi is displayed on the high-pressure fuel gauge.  The following can be the cause, except_____________.

Accepted Answer

defective high-pressure regulator

Answer

defective engine ECM wiring

Answer

stuck cylinder flow control solenoid

Answer

low CNG fuel cascade system pressure

Question 3

What is the compress natural gas engine mixer used for?

Accepted Answer

To blend air and gas before entering the intake.

Answer

To allow gas flow to enter the intake.

Answer

To allow gas flow to enter the exhaust.

Answer

To control gas flow before entering the intake.

Question 4

How can a vehicle equipped with a compressed natural gas system be identified?

Accepted Answer

It is marked with an NGV sign.

Answer

It has a natural gas tank.

Answer

The engine compartment must be checked.

Answer

The vehicle manual book must be checked.

Question 5

What is the natural gas vehicle (NGV) engine regulator used for?

Accepted Answer

To regulate NGV gas pressure from the tank.

Answer

To measure NGV gas from the tank.

Answer

To proportion NGV gas from the tank.

Answer

It is used for NGV gas residual from the tank.

Question 6

What must be done first to repair an EPA-certified CNG system that has failed emissions due to a failure of an expensive system component?

Accepted Answer

The system manufacturer must be checked for warranty.

Answer

The system must be modified.

Answer

Find a replacement component from a different manufacturer.

Answer

The part must be replaced and the customer must be charged to ensure timely repair.

Question 7

When checking the fuel line connections after a compressed natural gas conversion, which of these should be used?

Accepted Answer

Non-Ammonia Soap

Answer

Propane

Answer

Nitrogen

Answer

Carbon Dioxide

Question 8

The technician finds that the vehicle won't take fuel after replacing the CNG fuel tank. Which one of these might be the reason?

Accepted Answer

The manual lock-down valve(s) failed to open.

Answer

There’s a pinched O-ring on the receptacle line.

Answer

There’s an open circuit on the in-tank solenoid valve.

Answer

None of the above.

Question 9

What should a technician do if stress corrosion cracking is evident in a hoop-wrapped Type-2 cylinder?

Accepted Answer

The cylinder must be removed from service.

Answer

Use an approved coating to fix the damaged area.

Answer

Document the damage on the inspection form.

Answer

Stress corrosion cracking is normal.

Question 10

There is a no-start condition in the dedicated CNG vehicle. The following could be the cause, except _______________.

Accepted Answer

recurved timing

Answer

no fuel pressure

Answer

no ignition source

Answer

All of the above.