CEI CEI Fuel Systems & Engine Combustion 3

Question 1

Which ignition system problem is most likely to cause a significant spike in hydrocarbon (HC) emissions during an emission test?

Accepted Answer

Engine misfire due to a fouled spark plug or weak ignition coil, causing unburned fuel to exit through the exhaust

Answer

Engine misfire, whether from a fouled spark plug, weak coil, or damaged wire, sends raw unburned fuel into the exhaust, dramatically increasing HC emissions.

Question 2

What is the purpose of the positive crankcase ventilation (PCV) system, and what emission does it help control?

Accepted Answer

It routes crankcase blowby gases (containing unburned HC) back into the intake manifold to be burned rather than venting them to the atmosphere

Answer

The PCV system draws combustion blowby gases—primarily unburned hydrocarbons—from the crankcase and redirects them into the intake to be burned, preventing direct HC emissions to atmosphere.

Question 3

Fuel volatility, measured by Reid Vapor Pressure (RVP), is regulated seasonally in many US regions. Why is lower RVP fuel required during summer months?

Accepted Answer

Lower RVP reduces evaporative hydrocarbon emissions from fuel tanks and carburetors in hot weather, helping areas meet ozone standards

Answer

Higher temperatures increase fuel evaporation; requiring lower RVP fuels in summer reduces evaporative HC emissions (a VOC ozone precursor) from fuel systems and refueling operations.

Question 4

What effect does engine operating temperature have on CO emissions during a cold-start emission test?

Accepted Answer

Cold engines produce significantly more CO because the ECU runs a rich fuel mixture during warm-up and the catalytic converter is not yet at operating temperature

Answer

During cold start, the ECU enriches the mixture for driveability and the catalytic converter is below its light-off temperature (~250–300°C), so CO passes through unoxidized, causing a spike in CO emissions.

Question 5

A vehicle equipped with a selective catalytic reduction (SCR) system uses what reductant to chemically reduce NOx in diesel exhaust?

Accepted Answer

Diesel Exhaust Fluid (DEF), a urea-water solution that decomposes to ammonia, which reacts with NOx to form N2 and H2O

Answer

SCR systems inject DEF (32.5% urea in water) into the exhaust; the urea hydrolyzes to ammonia, which reacts with NOx over a vanadium or zeolite catalyst to produce harmless nitrogen gas and water.

CEI - Certified Emission Inspector Practice Test

CEI - Certified Emission Inspector Practice Test

CEI CEI Fuel Systems & Engine Combustion 3