DFFT Fuel Systems

Question 1

A vehicle cranks normally but will not start. The fuel injectors are pulsing but there is no spark. What system should be diagnosed?

Accepted Answer

The ignition system, including coils, crank sensor, and spark plugs

Answer

The fuel pump pressure output

Answer

The engine's compression ratio

Answer

The intake air temperature sensor

Question 2

A vehicle has poor performance and black smoke from the exhaust. What does this indicate about the fuel mixture?

Accepted Answer

The engine is running excessively rich with too much fuel

Answer

The engine is running lean with insufficient fuel

Answer

The catalytic converter is overheating

Answer

The EGR valve is stuck open

Question 3

A fuel pressure test shows pressure within specification at rest but drops rapidly during cranking. What does this indicate?

Accepted Answer

A weak fuel pump unable to maintain pressure under flow demand

Answer

A leaking fuel pressure regulator diaphragm

Answer

A clogged fuel filter causing high restriction

Answer

A faulty fuel injector leaking internally

Question 4

A vehicle starts normally but stalls at idle once it reaches operating temperature. What should be tested?

Accepted Answer

Idle air control valve operation and throttle body deposits

Answer

Fuel injector spray pattern

Answer

Fuel tank venting system

Answer

Cold start injector function

Question 5

What is the purpose of the fuel pressure regulator in a port injection system?

Accepted Answer

To maintain a constant pressure differential between the fuel rail and intake manifold

Answer

To prevent fuel from returning to the tank when the engine is off

Answer

To regulate fuel pump speed based on engine load

Answer

To filter contaminants from reaching the injectors

Question 6

A vehicle hesitates during acceleration from a stop. Fuel pressure is correct and spark is good. What should be checked next?

Accepted Answer

Injector duty cycle and volume output test

Answer

Battery voltage during cranking

Answer

Oxygen sensor switching frequency

Answer

EGR valve position at idle