Engine Performance & Diagnostics Flashcards
7 cards from real NAPA 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 & Diagnostics flashcards as text
A secondary ignition oscilloscope pattern shows a very high firing line and a short spark line on one cylinder. What is the most likely cause?
Answer: Open or high-resistance plug wire or wide plug gap
High resistance in the secondary circuit takes more voltage to fire, leaving less energy for spark duration.
A crankshaft position sensor code sets only when the engine is hot, and the engine stalls. What is the best test approach?
Answer: Use a scope to monitor the CKP signal while heating the sensor
Heat-related sensor failures are best confirmed by watching the live signal while recreating the condition.
A P0016 code indicates a crankshaft-camshaft correlation fault. Which is a common mechanical cause?
Answer: Stretched timing chain
A stretched timing chain changes cam position relative to the crankshaft, setting a correlation code.
Low engine oil pressure can trigger which code on an engine with variable valve timing?
Answer: Camshaft position actuator performance code
VVT actuators are oil-pressure controlled, so low pressure or dirty oil keeps them from reaching the commanded position.
Spark knock under load on an engine with a properly working knock sensor most likely points to which cause?
Answer: Carbon buildup raising compression or a lean condition
Carbon deposits raise compression and create hot spots, and lean mixtures burn hotter, both of which promote detonation.
A MAP sensor reads 101 kPa with the key on and engine off at sea level, and 30 kPa at warm idle. What do these readings indicate?
Answer: MAP sensor and engine vacuum are normal
About 101 kPa equals sea-level barometric pressure, and 30 kPa at idle shows good manifold vacuum.
A voltage drop test across the PCM ground circuit reads 0.6 V with the engine running. What should the technician conclude?
Answer: Excessive ground resistance that needs repair
Computer ground circuits should usually drop less than 0.1 V, so 0.6 V shows excessive resistance that can skew sensor readings.