Engine Performance & Tuning Flashcards
7 cards from real CPT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Engine Performance & Tuning flashcards as text
What does a vacuum leak downstream of the throttle body typically cause in engine operation?
Answer: Lean air-fuel mixture
A vacuum leak introduces unmetered air into the intake manifold, leaning out the air-fuel mixture beyond the intended ratio.
Which sensor is primarily responsible for enabling closed-loop fuel control in a modern engine management system?
Answer: Oxygen sensor
The oxygen sensor provides real-time exhaust gas feedback that the ECU uses to continuously correct fuel trim and maintain stoichiometry.
When diagnosing a misfire on a specific cylinder, swapping the ignition coil to another cylinder and observing if the misfire follows the coil indicates what?
Answer: A defective coil-on-plug unit
If the misfire moves to the new cylinder after swapping the coil, the coil itself is confirmed as the defective component.
What is the primary function of a variable valve timing (VVT) system?
Answer: Optimize cam phasing for power and efficiency across the RPM range
VVT advances or retards camshaft timing relative to crankshaft position to balance low-end torque with high-RPM power output.
A long-term fuel trim (LTFT) reading of +18% on Bank 1 most likely indicates what condition?
Answer: Lean condition on Bank 1 requiring added fuel
A high positive LTFT value shows the ECU is adding significant fuel to compensate for a lean condition, such as a vacuum leak or weak injector.
During a cylinder balance test, disabling an injector that causes little or no RPM drop indicates what about that cylinder?
Answer: That cylinder is already misfiring or not contributing
A cylinder that shows minimal RPM drop when its injector is cut off was already producing little power, pointing to a misfire or mechanical issue.
What is the purpose of an exhaust gas recirculation (EGR) valve in an engine?
Answer: Reintroduce exhaust gases to reduce NOx emissions
EGR dilutes the intake charge with inert exhaust gas, lowering peak combustion temperatures and reducing the formation of nitrogen oxides (NOx).