Advanced Engine Performance Specialist Flashcards

A knock sensor that fails or is disconnected will typically cause the ECM to:

Answer: Retard timing to a conservative default

Without valid knock feedback, the ECM retards timing for protection, often reducing power and economy.

On a returnless fuel system, fuel pressure is controlled primarily by:

Answer: The PCM varying pump duty cycle via a driver module

Returnless systems commonly use a PCM/fuel pump control module to vary pump speed and maintain target pressure.

A misfire that occurs only under load and high RPM, with secondary ignition showing high firing voltage, points to:

Answer: Worn spark plugs or a weak coil under demand

High required firing voltage under load indicates excessive gap or weak spark from worn plugs/coils.

When a scan tool shows the O2 sensor stuck at a high voltage (~0.9V), the condition usually indicates:

Answer: A rich exhaust or biased sensor

High O2 voltage corresponds to a rich mixture, though a contaminated/biased sensor can also read high.

A volumetric efficiency (VE) calculation is a useful advanced diagnostic to detect:

Answer: Restricted intake/exhaust or cam timing problems

Calculated VE compared to expected reveals breathing problems like restrictions or incorrect cam timing.

An EVAP system small leak (P0442) is most efficiently located using:

Answer: Smoke testing the EVAP system

Introducing smoke under low pressure makes the leak visible as escaping smoke.

If both short-term and long-term fuel trims are significantly negative across all load ranges, suspect:

Answer: High fuel pressure or a leaking injector

Negative trims mean the ECM is removing fuel to compensate for an inherently rich condition like high pressure or a leaking injector.