Fuel and Emission Systems Flashcards

What is the purpose of the fuel pump driver module in modern vehicles?

Answer: To control fuel pump speed based on engine demand, improving efficiency and reducing noise

The fuel pump driver module receives a command signal from the ECM and varies the voltage or PWM signal to the fuel pump, adjusting pump speed to match fuel demand rather than running at full speed constantly.

What is the function of the intake air temperature (IAT) sensor?

Answer: To provide air temperature data to the ECM for adjusting fuel delivery and ignition timing based on air density

The IAT sensor reports intake air temperature to the ECM. Cold air is denser (more oxygen per volume), requiring more fuel, while hot air is less dense, requiring less fuel. The ECM adjusts accordingly.

A four-gas exhaust analyzer shows high CO and high HC readings. What condition does this indicate?

Answer: A rich fuel mixture with incomplete combustion

High CO indicates a rich mixture (excess fuel not fully oxidized). High HC indicates unburned fuel passing through. Together, they point to a rich condition with incomplete combustion from excess fuel.

What is the function of the selective catalytic reduction (SCR) system in diesel vehicles?

Answer: To inject diesel exhaust fluid (DEF/urea) into the exhaust to chemically reduce NOx emissions

The SCR system injects a urea-based solution (DEF) into the exhaust stream where it decomposes into ammonia. The ammonia reacts with NOx over a catalyst, converting it into harmless nitrogen and water.

What is the primary cause of a lean misfire at idle?

Answer: An intake manifold vacuum leak allowing unmetered air to enter

A vacuum leak introduces unmetered air into the intake manifold, leaning out the mixture beyond the ECM's ability to compensate at idle. The lean mixture fails to ignite reliably, causing misfires.

How does the ECM detect a misfire?

Answer: By monitoring crankshaft speed variations through the crankshaft position sensor

The ECM monitors crankshaft rotational speed via the CKP sensor. When a cylinder misfires, it fails to contribute its power pulse, causing a measurable deceleration in crankshaft speed that the ECM identifies as a misfire.