ASE T2 DIESEL ENGINES CERTIFICATION
EXAM QUESTION AND CORRECT
ANSWERS (VERIFIED ANSWERS) PLUS
RATIONALES 2026 Q&A INSTANT
DOWNLOAD PDF
1. A diesel engine has low compression in one cylinder. Which condition is
MOST likely?
A. Restricted fuel filter
B. Faulty injector solenoid
C. Incorrect injection timing
D. Worn piston rings
Worn piston rings allow combustion pressure to leak past the piston,
reducing compression.
2. Excessive white smoke at cold start on a diesel engine usually indicates:
A. Oil burning
B. Unburned fuel
C. Overheated engine
D. Excessive boost pressure
White smoke is typically caused by unburned fuel due to low combustion
temperatures.
3. A common rail diesel system controls fuel pressure using:
A. Mechanical governor
B. Injector nozzle size
C. High-pressure pump and pressure regulator
D. Turbocharger wastegate
Rail pressure is electronically regulated by the high-pressure pump and
pressure control devices.
,4. A diesel engine that lacks power under load but runs smoothly at idle may
have:
A. Incorrect valve lash
B. Restricted air intake
C. Faulty glow plugs
D. High compression ratio
A restricted air intake limits airflow, reducing power especially under
load.
5. Excessive black smoke during acceleration indicates:
A. Coolant contamination
B. Lean air-fuel ratio
C. Overfueling or lack of air
D. Retarded injection timing
Black smoke is caused by incomplete combustion due to excess fuel or
insufficient air.
6. Which component directly atomizes diesel fuel?
A. High-pressure pump
B. Fuel rail
C. Injector nozzle
D. Fuel filter
The injector nozzle breaks fuel into a fine spray for efficient combustion.
7. A failed glow plug will most likely cause:
A. Poor fuel economy
B. Hard cold starting
C. Excessive boost pressure
D. Engine overheating
Glow plugs heat the combustion chamber to aid cold starting.
8. What is the primary function of a turbocharger?
A. Reduce exhaust emissions
B. Increase air density in the intake
C. Cool intake air
D. Reduce engine noise
Turbochargers force more air into the engine, increasing power output.
, 9. A diesel engine uses compression ignition, meaning:
A. Spark plugs ignite fuel
B. Fuel ignites at low pressure
C. Fuel ignites due to heat from compressed air
D. Fuel ignites outside the cylinder
High compression raises air temperature enough to ignite diesel fuel.
10.A clogged diesel particulate filter (DPF) will cause:
A. Increased engine speed
B. Loss of power and high exhaust backpressure
C. Lower exhaust temperatures
D. Improved fuel economy
A clogged DPF restricts exhaust flow, reducing engine performance.
11.What sensor is used to calculate fuel delivery in a common rail diesel?
A. Throttle position sensor
B. Mass air flow sensor
C. Knock sensor
D. Vehicle speed sensor
The MAF sensor measures intake air for precise fuel metering.
12.Excessive crankcase pressure on a diesel engine may be caused by:
A. Restricted exhaust
B. Blow-by from worn cylinders
C. Faulty glow plugs
D. Overfilled fuel tank
Blow-by allows combustion gases to enter the crankcase.
13.Diesel engines generally operate with:
A. Lower compression ratios than gasoline engines
B. Higher compression ratios than gasoline engines
C. Equal compression ratios
D. No compression ratio
High compression is required for compression ignition.
14.What is the function of the EGR system?
A. Increase engine speed
B. Improve turbo efficiency
EXAM QUESTION AND CORRECT
ANSWERS (VERIFIED ANSWERS) PLUS
RATIONALES 2026 Q&A INSTANT
DOWNLOAD PDF
1. A diesel engine has low compression in one cylinder. Which condition is
MOST likely?
A. Restricted fuel filter
B. Faulty injector solenoid
C. Incorrect injection timing
D. Worn piston rings
Worn piston rings allow combustion pressure to leak past the piston,
reducing compression.
2. Excessive white smoke at cold start on a diesel engine usually indicates:
A. Oil burning
B. Unburned fuel
C. Overheated engine
D. Excessive boost pressure
White smoke is typically caused by unburned fuel due to low combustion
temperatures.
3. A common rail diesel system controls fuel pressure using:
A. Mechanical governor
B. Injector nozzle size
C. High-pressure pump and pressure regulator
D. Turbocharger wastegate
Rail pressure is electronically regulated by the high-pressure pump and
pressure control devices.
,4. A diesel engine that lacks power under load but runs smoothly at idle may
have:
A. Incorrect valve lash
B. Restricted air intake
C. Faulty glow plugs
D. High compression ratio
A restricted air intake limits airflow, reducing power especially under
load.
5. Excessive black smoke during acceleration indicates:
A. Coolant contamination
B. Lean air-fuel ratio
C. Overfueling or lack of air
D. Retarded injection timing
Black smoke is caused by incomplete combustion due to excess fuel or
insufficient air.
6. Which component directly atomizes diesel fuel?
A. High-pressure pump
B. Fuel rail
C. Injector nozzle
D. Fuel filter
The injector nozzle breaks fuel into a fine spray for efficient combustion.
7. A failed glow plug will most likely cause:
A. Poor fuel economy
B. Hard cold starting
C. Excessive boost pressure
D. Engine overheating
Glow plugs heat the combustion chamber to aid cold starting.
8. What is the primary function of a turbocharger?
A. Reduce exhaust emissions
B. Increase air density in the intake
C. Cool intake air
D. Reduce engine noise
Turbochargers force more air into the engine, increasing power output.
, 9. A diesel engine uses compression ignition, meaning:
A. Spark plugs ignite fuel
B. Fuel ignites at low pressure
C. Fuel ignites due to heat from compressed air
D. Fuel ignites outside the cylinder
High compression raises air temperature enough to ignite diesel fuel.
10.A clogged diesel particulate filter (DPF) will cause:
A. Increased engine speed
B. Loss of power and high exhaust backpressure
C. Lower exhaust temperatures
D. Improved fuel economy
A clogged DPF restricts exhaust flow, reducing engine performance.
11.What sensor is used to calculate fuel delivery in a common rail diesel?
A. Throttle position sensor
B. Mass air flow sensor
C. Knock sensor
D. Vehicle speed sensor
The MAF sensor measures intake air for precise fuel metering.
12.Excessive crankcase pressure on a diesel engine may be caused by:
A. Restricted exhaust
B. Blow-by from worn cylinders
C. Faulty glow plugs
D. Overfilled fuel tank
Blow-by allows combustion gases to enter the crankcase.
13.Diesel engines generally operate with:
A. Lower compression ratios than gasoline engines
B. Higher compression ratios than gasoline engines
C. Equal compression ratios
D. No compression ratio
High compression is required for compression ignition.
14.What is the function of the EGR system?
A. Increase engine speed
B. Improve turbo efficiency
