Automotive Service Excellence (ASE) A8 Engine Performance flashcards

Catalytic converter efficiency is determined by comparing the switching patterns of the upstream and downstream oxygen sensors.

• Healthy converter: Upstream fluctuates rapidly, downstream is steady.
• Failing converter: Both sensors fluctuate rapidly and similarly.
• P0420/P0430 DTCs indicate below-threshold efficiency.

Memory trick: Upstream dances, downstream sleeps; if both dance, catalyst weeps.

A vacuum leak at a specific intake manifold runner can cause a lean misfire on that cylinder, often more noticeable at idle due to higher manifold vacuum.

• Misfire isolated to one or few cylinders.
• More pronounced at idle/low RPM.
• Caused by unmetered air entry.
• Can be detected with smoke test or carb cleaner spray.

Memory trick: Misfire on one, check the air run.

A clogged catalytic converter causes a loss of engine power, especially under heavy acceleration, due to restricted exhaust flow. Symptoms may be less noticeable at idle.

• Loss of power under load.
• Engine may feel 'choked' or 'bog down'.
• Can cause excessive heat under the vehicle.
• Backpressure test can confirm.

Memory trick: Heavy load, exhaust choked.

The canister vent valve controls the flow of fresh air into the charcoal canister during purge cycles and seals the EVAP system for leak detection tests.

• Normally open, closes for leak tests and some purge cycles.
• Failure can cause EVAP DTCs (e.g., P0440, P0442, P0446).
• A stuck-open valve prevents the EVAP system from pressurizing.

Memory trick: Smoke at canister? Vent's the culprit, not a prankster.

A common cause of a P0442 (Small EVAP Leak) DTC is a faulty or improperly tightened fuel filler cap.

• Fuel cap is part of the sealed EVAP system.
• Often overlooked in diagnostics.
• Easy to check and replace.

Memory trick: Small leak's quest, check the cap first, then the rest.

The fuel pump check valve maintains residual fuel pressure in the system after the pump turns off and prevents fuel from flowing back to the tank, crucial for consistent pressure.

• Located within the fuel pump assembly.
• Prevents fuel drain-back.
• Failure causes extended cranking and pressure drop on deceleration.

Memory trick: Fuel pressure should hold steady; if it drops, the check valve is on vacation.

A diagnostic trouble code (DTC) indicating an electrical or mechanical issue with the canister vent valve or its control circuit.

• P0446 is a common DTC for this issue.
• Can be caused by open/short circuits, faulty vent valve, or corroded connectors.
• An audible click doesn't guarantee full functionality.

Memory trick: Vent valve clicks, but the code sticks, internal tricks.

A component in the fuel rail designed to absorb pressure fluctuations caused by fuel injector opening and closing, ensuring smooth fuel delivery.

• Reduces noise and vibration in the fuel system.
• Helps maintain stable fuel pressure.
• Can leak if its diaphragm or housing fails.

Memory trick: Engine smells, near the rail, damper's tale.

When the downstream oxygen sensor voltage closely follows the upstream oxygen sensor voltage, it indicates the catalytic converter has lost its oxygen storage capacity and is no longer efficient.

• Normal operation: downstream O2 is relatively stable.
• Failure: downstream O2 fluctuates like upstream.
• Common cause of P0420/P0430 DTCs.

Memory trick: If the downstream O2 is a copycat, the catalyst is a goner.

Exhaust gas analysis results indicating an air-fuel mixture with too much fuel relative to air, leading to incomplete combustion.

• High Hydrocarbons (HC) from unburnt fuel.
• High Carbon Monoxide (CO) from incomplete combustion.
• Low Nitrogen Oxides (NOx) due to reduced combustion temperatures.

Memory trick: HC/CO high, NOx low, rich mixture's flow.

Rapid and erratic clicking (chattering) of a relay is a strong indicator of low control voltage or insufficient power supply to the relay coil.

• Commonly caused by low battery voltage.
• Can also be caused by poor ground connections.
• Prevents consistent power delivery to the controlled component.
• Check voltage at relay terminals.

Memory trick: Relay chatter, battery's sad patter.

A diagnostic procedure used to locate leaks in the exhaust system by introducing smoke under pressure.

• Engine must be off to prevent smoke expulsion.
• Tailpipe must be blocked to pressurize the system.
• Smoke is introduced into the tailpipe or a convenient access point.

Memory trick: Smoke in, engine off, tailpipe tight, leaks in sight.

A restricted fuel filter limits fuel flow, causing low fuel pressure, especially under acceleration when fuel demand is high, leading to power loss and lean conditions.

• Reduces fuel flow capacity.
• Symptoms worsen under load.
• Can cause P0087 (low fuel pressure) DTC.

Memory trick: If fuel pressure drops when the engine 'drinks' hard, the filter is clogged.

A diagnostic test that measures how quickly the fuel system loses residual pressure after the fuel pump is turned off.

• Identifies leaks in the fuel pump check valve, fuel injectors, or fuel lines.
• Crucial for diagnosing long crank times or hard starts after sitting.
• Requires a fuel pressure gauge and monitoring pressure over time.

Memory trick: Long crank, no fuel tank, pressure's sank.

A condition where the turbocharger wastegate valve remains open, allowing exhaust gases to bypass the turbine, preventing boost generation.

• Leads to insufficient boost pressure.
• Causes significant loss of engine power.
• Can be due to a faulty actuator, seized rod, or damaged wastegate valve.

Memory trick: Wastegate open, boost is broken, power unspoken.

Positive fuel trims indicate the Engine Control Module (ECM) is adding more fuel than calculated because the oxygen sensors detect a lean condition.

• Corrects for insufficient fuel delivery or excess air.
• Can be short-term (STFT) or long-term (LTFT).
• High positive trims (>+10% to +20%) often indicate a fault.

Memory trick: Bank's lean, fuel trims keen, injector scene.

A MAF sensor that over-reports airflow at lower RPMs will cause negative fuel trims (rich condition) as the ECM tries to compensate. Trims may normalize at WOT when the ECM uses open-loop fueling.

• Causes negative fuel trims.
• Often more pronounced at idle/low RPM.
• May normalize at WOT.
• Check MAF sensor readings against known good values.

Memory trick: Negative trims, MAF's big lie.

EVAP system components directly mounted on or connected to the fuel tank include the fuel tank pressure sensor, rollover valve, and associated hoses, all critical for leak integrity.

• Fuel tank pressure sensor measures tank pressure.
• Rollover valve prevents fuel spillage.
• Hoses connect tank to rest of EVAP system.

Memory trick: After a tank swap, check the connections made to the tank itself.

A leak in the fuel pressure damper diaphragm allows raw fuel to be drawn into the intake manifold through the vacuum line, causing a rich condition.

• Symptoms include strong gasoline smell, rough idle (especially vacuum-related), and poor fuel economy.
• Often mistaken for a leaking injector or external leak.
• Diagnostic involves checking for fuel in the damper's vacuum line.

Memory trick: Smell of gas, rough idle mess, damper's stress, intake's excess.

The fuel pump check valve maintains residual fuel pressure in the system after the pump turns off, preventing hard starts due to fuel draining back.

• Symptoms: Hard starts (especially after sitting), long crank times.
• Diagnostic: Rapid fuel pressure drop during a leak-down test.
• Located within or near the fuel pump assembly.

Memory trick: Pressure drop, check valve's flop, hard start won't stop.

Consistently negative fuel trims indicate the ECM is reducing fuel delivery because the system is running rich, often due to excess fuel pressure or injector issues.

• ECM detects excess fuel in exhaust.
• Reduces injector pulse width.
• Common causes: high fuel pressure, leaking injectors, faulty O2 sensor.

Memory trick: Too much fuel makes the engine 'rich' and unhappy, demanding less fuel.

A P0455 (EVAP Large Leak) often points to a significant breach in the EVAP system, which can be identified by a smoke test. Common sites include the fuel cap, filler neck, or the fuel pump module seal.

• Indicates a large leak (e.g., >0.040' orifice equivalent).
• Smoke test is the primary diagnostic tool.
• Fuel pump module seal is a frequent failure point.
• Can also be caused by a missing or loose fuel cap.

Memory trick: Smoke points to the leak.

The Evaporative Emission Control System (EVAP) monitors for small leaks, typically indicated by DTC P0442, when fuel vapor escapes.

• Monitors for leaks in the fuel vapor recovery system.
• Small leaks can be caused by cracks in hoses or loose caps.
• DTC P0442 is common for small EVAP leaks.

Memory trick: EVAP leaks are like tiny gas ghosts escaping, triggering specific codes.

A breach in the seal between the exhaust manifold and the cylinder head, allowing exhaust gases to escape.

• Often causes a ticking or 'putt-putt' sound.
• Sound typically louder when cold, may diminish as engine warms.
• Can lead to exhaust leaks before O2 sensor, affecting fuel trims.

Memory trick: Cold tick, manifold's trick, gasket's quick.

In a GDI system, the high-pressure fuel pump relies on adequate fuel supply from the low-pressure fuel pump. Insufficient low-pressure supply will directly limit the high-pressure output.

• GDI uses two fuel pumps: low-pressure (tank to HP pump) and high-pressure (HP pump to injectors).
• Low-pressure pump typically 40-80 PSI.
• High-pressure pump typically 500-3000 PSI.
• Diagnose low-pressure side first if both are low.

Memory trick: Low flow in, low pressure out.

A vacuum leak allows unmetered air into the engine, disrupting the calculated air-fuel ratio and leading to various performance issues.

• Causes a lean air-fuel mixture.
• Can result in rough idle, misfires, and P0171/P0174 DTCs.
• Often identified by a hissing sound or smoke test.

Memory trick: Hissing intake, lean mistake, engine's ache.

A blockage in the small tubes connecting the DPF to the differential pressure sensor, leading to inaccurate and often falsely high pressure readings.

• Causes false DPF restriction warnings.
• Can trigger unnecessary regeneration cycles or derate.
• Often overlooked in DPF diagnostics.

Memory trick: High delta P, engine's free, sensor tube's the key.

A stuck-open EGR valve in a diesel engine allows exhaust gases to continuously enter the intake, reducing available oxygen for combustion.

• Symptoms: Reduced power, black smoke (due to lean condition), rough idle.
• Diagnostic: High EGR position readings (actual or commanded) at inappropriate times.
• Leads to incomplete combustion.

Memory trick: EGR open, power's low, black smoke's flow.

A rich condition is indicated by black smoke and a downstream oxygen sensor consistently reading high voltage (above 0.7V), as the catalytic converter is overwhelmed and cannot store oxygen.

• Black smoke is a visual indicator of richness.
• Upstream O2 should still switch if engine tries to compensate.
• Downstream O2 stays high due to excess unburnt fuel.

Memory trick: High downstream voltage + black smoke = too much gas.

A vacuum gauge needle that drops immediately to zero after the engine is turned off, indicating a failure to hold vacuum.

• Strongly suggests a significant vacuum leak.
• Confirms the intake manifold cannot maintain its vacuum.
• Requires inspection of vacuum hoses, gaskets, and components.

Memory trick: Shutdown Drop? Vacuum Leak's the Stop!

The reduction in voltage observed in the primary ignition circuit, especially during engine cranking, due to normal current draw and circuit resistance.

• Normal for voltage to drop during cranking.
• Must remain above minimum specification for proper spark.
• Excessive drop indicates high resistance or weak battery.

Memory trick: Cranking voltage always drops, but not too low.

Corrosion on distributor cap terminals introduces excessive resistance into the secondary ignition circuit, reducing the high voltage delivered to the spark plugs and causing misfires.

• Increases resistance in secondary circuit.
• Reduces spark plug voltage.
• Causes misfires or rough idle.

Memory trick: Corrosion's grip, the spark can't skip.

A severe engine noise caused by excessive clearance between the connecting rod and crankshaft journal due to bearing wear.

• Deep, heavy, rhythmic 'thump' or 'clunk' noise.
• Directly proportional to engine RPM.
• Often heard from deep within the engine block.
• Indicates serious internal engine damage requiring immediate attention.

Memory trick: Deep 'thump' with RPM's call, rod bearing's about to fall!

A significantly lower compression reading in one cylinder compared to others, indicating a mechanical fault specific to that cylinder.

• Suggests a localized mechanical problem.
• Common causes include worn piston rings, burnt valves, or head gasket leaks.
• Requires further diagnostic steps like a wet compression test or cylinder leakage test.

Memory trick: Compression's Drop: Rings, Valves, or Head's Flop.

A diagnostic step to verify that the Engine Control Module (ECM) is receiving proper electrical power and ground connections when symptoms indicate a non-functional or non-communicating ECM.

• Essential for ECM operation and communication.
• Check before condemning ECM.
• Use wiring diagrams to locate correct terminals.

Memory trick: No spark, no comm? Check ECM's home (power/ground).

A diagnostic procedure where a small amount of oil is added to a cylinder with low compression, then the compression test is repeated to help identify the source of the leak.

• If compression increases significantly, piston rings are likely worn.
• If compression remains low, valve or head gasket issues are more likely.
• Performed after a 'dry' compression test shows low results.

Memory trick: Compression tells the seal's tale, low pressure means a likely fail.

An open circuit in the secondary winding of an ignition coil prevents the high voltage necessary for spark plug firing, even if the primary circuit functions correctly.

• Primary waveform appears normal.
• No secondary voltage or spark is produced.
• Common cause of misfires or no-start conditions.

Memory trick: Primary's fine, but secondary's silent, no spark for the engine's plight.

An oscilloscope waveform showing high firing voltage (kV) and a very short spark line duration, indicative of high resistance or an open circuit in the secondary ignition.

• High kV to jump large/difficult gap.
• Short duration due to inability to sustain spark.
• Common causes: bad wire, severely fouled plug, wide plug gap.

Memory trick: High voltage, short spark: open circuit's stark mark.

The electrical resistance of the primary winding within an ignition coil, which controls the current flow that builds the magnetic field.

• Too high resistance reduces primary current.
• Reduced primary current weakens magnetic field.
• Weaker magnetic field results in weaker secondary spark.

Memory trick: Primary current builds the spark, resistance restricts it.

A malfunction within the Engine Control Module (ECM) where the internal circuit responsible for switching an ignition coil's primary circuit fails, preventing spark generation for that cylinder.

• ECM provides the ground/trigger.
• Constant voltage on control wire indicates no switching.
• Often specific to one cylinder's driver.

Memory trick: The 'brain' (ECM) 'commands' the 'spark', if the command is 'stuck', no spark.

A condition in an ignition coil where its internal electrical resistance changes dramatically (typically increases) when subjected to heat, causing intermittent misfires or no-start conditions when hot.

• Resistance changes with temperature.
• Often causes hot-start or hot-stall issues.
• Requires testing when hot to diagnose.

Memory trick: The 'hotter' the coil, the 'higher' its 'resistance', the 'weaker' the spark.

A diagnostic test where individual cylinders are momentarily disabled to assess their power contribution. A significant drop in engine RPM when disabled indicates normal power production.

• Performed by disabling ignition or fuel to a cylinder.
• Significant RPM drop = cylinder contributing power normally.
• Little or no RPM drop = cylinder not contributing power (misfire).

Memory trick: RPM drop is proof of power's flow.

Diagnosing engine noises or vibrations that originate from engine-driven accessories or their mounting components.

• Localized noise/vibration points to specific accessory.
• Use a stethoscope to pinpoint the source.
• Often not directly related to engine internal health.

Memory trick: Listen close, the accessory's dose.

A specific vacuum gauge pattern indicating an obstruction in the exhaust system, preventing efficient gas flow.

• Normal or slightly low idle vacuum.
• Drops on acceleration.
• Slow, sluggish return to idle vacuum after revving.
• Can also cause exhaust system components to overheat.

Memory trick: Vacuum returns slow and steady, exhaust restriction is already ready!

A vacuum gauge reading that is normal at idle but drops significantly and fluctuates erratically under acceleration, indicating valves are not closing properly at higher RPMs.

• Normal idle vacuum.
• Erratic and significant drop under acceleration.
• Caused by valves floating due to weak springs.

Memory trick: Erratic drop on acceleration? Springs are weak, valves are dancing.

The CMP sensor monitors the camshaft's rotational position, providing crucial data to the ECM for accurate ignition timing and fuel injection synchronization.

• Works with the Crankshaft Position Sensor (CKP) for engine synchronization.
• Its signal helps the ECM determine which cylinder is at its compression stroke.
• A faulty CMP can cause misfires, no-start conditions, or stalling due to incorrect ignition/fuel timing.

Memory trick: CMP knows the cam, CKP knows the crank; together, they time the engine.

A diagnostic procedure where a small amount of oil is added to a cylinder with low dry compression. A significant increase in pressure indicates worn piston rings.

• Follows a low dry compression reading.
• Oil temporarily seals piston ring gaps.
• Significant pressure increase confirms worn rings.

Memory trick: Oil boosts compression? Rings are the mission!

High voltage leakage occurs when ignition voltage escapes to ground before reaching the spark plug, often exacerbated by humidity, and can be visually detected by observing arcing in a dark environment.

• Causes misfires, especially in humid conditions.
• Can be seen as visible arcing in the dark.
• Often related to cracked insulation or poor connections.

Memory trick: Water and dark reveal the spark's hidden arc.

A diagnostic symptom of oil consumption where blue-gray smoke is emitted from the exhaust primarily when accelerating after a period of idling, indicating leaking valve stem seals.

• Blue-gray smoke from exhaust.
• Most noticeable during acceleration after prolonged idle.
• Indicates oil seeping past valve stem seals during high vacuum conditions.

Memory trick: Blue smoke after idle? Valve seals are wild!

A secondary ignition waveform showing high firing voltage and short spark duration often indicates excessive resistance or an overly wide gap in the secondary circuit, forcing the coil to work harder.

• High kV = high resistance or large gap.
• Short duration = energy quickly depleted.
• Indicates difficulty in spark discharge.

Memory trick: High climb, quick fall – resistance makes the spark stall.

Assessing the condition of spark plug electrodes and insulators to determine their service life and identify potential engine issues.

• Electrode erosion widens the gap.
• Worn plugs require higher voltage to fire.
• Can lead to misfires and reduced fuel economy.

Memory trick: Look, Measure, Decide: Is the spark plug ready to be retired?

When all engine cylinders exhibit significantly lower compression readings than specified, indicating a widespread issue affecting the entire engine's sealing capability.

• Often points to a general engine timing problem.
• Could also be severely worn camshaft lobes or lifters.
• Rarely caused by uniform wear of piston rings or valves across all cylinders simultaneously.

Memory trick: Low compression everywhere? Check the engine's time and rhythm.

Diagnosing vibrations caused by rotating components within the engine, such as the crankshaft, flywheel, or harmonic balancer.

• Vibration is directly proportional to engine RPM.
• Present at idle and throughout the RPM range.
• Felt throughout the chassis, steering wheel, and floorboards.
• Requires ruling out external engine components and accessories.

Memory trick: If the shake matches the engine's pace, internal imbalance is the case!

Severe spark plug electrode erosion and insulator cracks are indicators of extreme heat, commonly caused by pre-ignition or detonation in the combustion chamber.

• Pre-ignition: ignition before spark.
• Detonation: uncontrolled secondary ignition.
• Both cause excessive heat and pressure.

Memory trick: Cracked insulator, eroded tip – too hot, like a fiery dip!

A diagnostic test that assesses the power contribution of individual cylinders by observing RPM changes when disabling each cylinder's ignition or fuel.

• Significant RPM drop indicates a healthy, contributing cylinder.
• Little to no RPM drop indicates a weak or dead cylinder.
• Can be performed by selectively disabling spark or fuel.

Memory trick: Balanced power makes the engine hum, imbalance tells a problem to come.

An oscilloscope is an invaluable tool for diagnosing intermittent electrical faults, especially in ignition systems, as it can visually capture transient waveform anomalies that might not trigger a diagnostic trouble code.

• Captures real-time electrical signals.
• Reveals subtle waveform deviations.
• Effective for transient and intermittent faults.

Memory trick: For a stumble's secret, scope's the key, revealing what's hidden for all to see.

A diagnostic technique where a Coil-On-Plug (COP) ignition coil from a misfiring cylinder is exchanged with a coil from a properly functioning cylinder to determine if the coil is faulty.

• Identifies a defective ignition coil quickly.
• If misfire moves, coil is bad.
• If misfire stays, look elsewhere.

Memory trick: Coil swap is the quick way to solve a COP misfire.

Identifying the source of rhythmic tapping or ticking sounds in an engine, often indicative of valvetrain issues.

• Top-end noise suggests valvetrain (lifters, rockers).
• Frequency increases with RPM.
• Often more noticeable when cold due to oil viscosity.

Memory trick: Listen to the engine's song, it tells where things went wrong.

Black, dry, powdery carbon deposits on spark plugs, typically indicating an overly rich air-fuel mixture or incomplete combustion.

• Caused by too much fuel or too little air.
• Leads to misfires and poor performance.
• Common causes: clogged air filter, faulty O2 sensor, leaking injector.

Memory trick: Sooty plugs mean too much fuel, not enough air.

Ignition timing retardation commanded by the ECM due to a faulty knock sensor incorrectly detecting engine knock, even when actual knock is not present.

• Leads to power loss and reduced fuel economy.
• Often no DTCs related to misfires are set.
• Requires diagnosis of knock sensor and related wiring/ECM.

Memory trick: Knock sensor's false alarm retards timing, stealing power.