GM Fuel Systems and Emissions 3

Question 1

What pressure does GM specify for the high-pressure fuel pump outlet on a typical GDI engine during full-load operation?

Accepted Answer

1,000-2,900 psi

Answer

45-65 psi

Answer

200-500 psi

Answer

3,500-5,000 psi

Question 2

Which GM scan tool function allows a technician to perform a fuel injector balance test to identify a faulty injector?

Accepted Answer

Injector Balance Test under Special Functions in GDS2

Answer

Fuel System Trim Reset in GDS2

Answer

Oxygen Sensor Heater Test via Tech2

Answer

MAF Sensor Rationality Check in GDS2

Question 3

What is the function of the charcoal canister in a GM EVAP system?

Accepted Answer

Adsorb and store fuel vapor from the fuel tank until the engine can purge it

Answer

Filter particulates from the incoming air supply to the fuel tank

Answer

Regulate fuel tank pressure by acting as a mechanical pressure relief device

Answer

Separate water from fuel before it reaches the high-pressure pump

Question 4

When performing an EVAP system small leak test on a GM vehicle, what leak rate defines a 'small leak' per OBD-II standards?

Accepted Answer

0.020-inch diameter equivalent orifice leak

Answer

Greater than 0.040-inch diameter equivalent

Answer

0.010-inch diameter equivalent orifice leak

Answer

Any detectable leak regardless of size

Question 5

On a GM flex-fuel vehicle, how does the PCM compensate for a higher ethanol blend (E85) compared to E10 gasoline?

Accepted Answer

Advances ignition timing and increases fuel injector pulse width to account for ethanol's lower energy density

Answer

Retards ignition timing and reduces fuel injector pulse width

Answer

Raises idle speed and disables EGR to reduce combustion temperature

Answer

Lowers fuel rail pressure and opens the purge valve more frequently

Question 6

What is the most likely cause of a GM vehicle's oxygen sensor reading that is fixed (stuck) at approximately 0.45V and not switching?

Accepted Answer

Sensor contamination, internal failure, or an exhaust system restriction causing the sensor to lose switching ability

Answer

Normal closed-loop operation at stoichiometric air-fuel ratio

Answer

A rich mixture caused by a stuck-open fuel pressure regulator

Answer

PCM commanding open-loop operation during a cold start

Question 7

Which GM program provides certified technicians with updated calibration files (calibrations/tunes) to address emissions-related performance issues identified after vehicle production?

Accepted Answer

Technical Service Bulletin (TSB) and Service Programming System (SPS) via GDS2

Answer

GM Global Technical Center (GTC) calibration portal

Answer

Goodwrench factory recall hotline

Answer

GM Dealer Advantage online parts catalog