Ten ASE A8 Engine Performance questions in the ASE format: four options, one best answer. They are free to use, print and share, and there is nothing to sign up for on this page.
01How to use these
The questions come from the ToolboxPrep A8 bank and are spread across the test's content areas in the proportion the ASE test specification gives them: A (General Diagnosis), B (Ignition System Diagnosis and Repair), C (Fuel, Air Induction and Exhaust Systems Diagnosis and Repair), D (Emissions Control Systems Diagnosis and Repair), E (Computerized Engine Controls Diagnosis and Repair). Answer each one before opening the explanation. Every explanation covers all four options, because knowing why the wrong answers are wrong is most of the skill.
- Pace. The A8 test gives you 75 minutes for 60 questions (50 scored, 10 unscored), about 1 min 15 s a question. Try these at that pace.
- Print. The printed version shows the questions and the answer key without the explanations, so it works as a handout.
02The questions
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A customer says the engine hesitates only when merging onto the freeway on hot afternoons, and no DTCs are stored. Before testing any part, the technician drives the vehicle under those conditions. What is the main purpose of this road test?
- So the PCM can store a freeze frame of it
- So the engine reaches closed loop first
- To reproduce the customer's complaint
- To let the PCM run its misfire monitor
Show the answer
C. Correct. Feeling the hesitation under the load and heat the customer describes proves the complaint is real and shows the conditions that set it off, which points testing at the systems that matter then. A fault that cannot be reproduced cannot be shown to be fixed afterward.
Why not the others
A. A freeze frame is stored only when a DTC sets, and a hesitation often sets none. The road test under the customer's conditions is made to feel the fault and confirm when it happens.
B. A warm engine goes into closed loop in ordinary driving, which needs no freeway merge on a hot afternoon. Driving under those conditions is done to confirm the fault itself and what brings it on.
D. Misfire detection is a continuous monitor that runs in normal driving without special conditions, and a hesitation is not necessarily a misfire. The road test is for confirming the fault and the conditions that cause it.
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On an engine with shim-type mechanical lifters, the manufacturer specifies intake valve clearance of 0.006 to 0.010 in. (0.15 to 0.25 mm), measured cold. With the engine cold, a feeler gauge measures 0.003 in. (0.08 mm) on one intake valve. What does this reading mean?
- Within the manufacturer's allowed range
- Too loose; the valve train will tick
- Too tight; the valve may not seat hot
- Too tight; the valve will open less far
Show the answer
C. Correct. 0.003 in. is below the 0.006 in. minimum, so there is too little clearance. As the valve heats and its stem grows, a tight valve can be held slightly open, losing compression and burning the valve and seat; a thinner shim restores the clearance.
Why not the others
A. The allowed range is 0.006 to 0.010 in., and 0.003 in. falls below its lower limit, so the clearance is out of specification on the tight side.
B. Loose clearance would be larger than 0.010 in. This reading of 0.003 in. is smaller than the 0.006 in. minimum, so the valve is too tight, not too loose.
D. The clearance is too tight, but tight clearance makes the valve open earlier, farther and longer, not less. The risk is a valve that does not fully seat when hot.
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On most OBD II vehicles, how does the PCM detect that a cylinder has misfired?
- A pressure pulse in the MAP sensor signal
- A drop in that cylinder's coil primary current
- A spike in the knock sensor signal at that cylinder
- A brief slowing of the crankshaft on the CKP signal
Show the answer
D. Correct. Each firing cylinder speeds the crankshaft up slightly, and the PCM times the CKP teeth to see it; a cylinder that fails to fire lets the crankshaft slow during its power stroke. The PCM counts those events for each cylinder and sets a misfire DTC when they pass its threshold.
Why not the others
A. The MAP sensor reports manifold pressure for the PCM's load calculation and does not identify which cylinder failed to fire. The PCM flags a misfire when a cylinder's power stroke fails to accelerate the crankshaft.
B. The PCM can watch its coil driver circuits for electrical faults, but a coil can draw normal primary current while the cylinder still fails to burn, as with a fouled plug, a lean cylinder or low compression. Misfire is judged from crankshaft speed.
C. The knock sensor listens for the sharp vibration of detonation; a cylinder that does not fire makes no such vibration. Misfire is detected from the crankshaft slowing between CKP teeth.
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The cylinder 1 coil-on-plug coil on a high-mileage fleet van has been replaced twice in six months for a misfire, and the misfire is back. The removed coil's boot is swollen and soft, and the spark plug well below it holds engine oil. Which of these is the root cause to repair?
- A failing PCM driver for the cylinder 1 coil
- A leaking cylinder 1 spark plug tube seal
- A cylinder 1 spark plug of the wrong heat range
- A spark plug overtightened in the cylinder 1 head
Show the answer
B. Correct. Oil in the plug well soaks into the coil boot, which swells and softens until the spark tracks through or around it. The leaking seal is the root cause, so each new coil fails the same way until the seal is replaced and the well is cleaned.
Why not the others
A. A driver fault would stop or weaken the coil's switching, but it cannot put oil in the plug well or swell the boot. The oil reaching the boot through a leaking seal is what keeps destroying the coils.
C. Heat range affects how hot the plug tip runs inside the combustion chamber; it has no effect on the boot or on oil collecting in the well. The oil comes from a leaking plug tube seal.
D. Overtightening can damage the plug or the threads in the head, but it does not bring oil into the plug well or swell the boot. The swollen boot and the oil in the well point to the leaking tube seal.
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A vehicle stumbles and sometimes stalls on long curves and freeway ramps, but only when the fuel gauge reads below one-quarter; with more fuel in the tank it never happens. Fuel pressure and volume tested with the tank half full are within the manufacturer's specifications. Which of these could be the cause?
- A cracked reservoir in the fuel pump module
- A partly restricted inline fuel filter
- A fuel level sender with a worn resistor card
- A pump with worn armature bushings
Show the answer
A. Correct. The module's reservoir (bucket) keeps a pool of fuel around the pump inlet so the pump stays covered when fuel sloshes to one side of the tank. If it is cracked or not being refilled, a low fuel level on a long curve uncovers the inlet and the pump draws air, starving the engine until the fuel settles.
Why not the others
B. A restricted filter limits flow at every fuel level and would have shown up as low volume on the check made with the tank half full. A fault that appears only with low fuel on curves points to the pickup area inside the tank.
C. A worn sender card makes the gauge read wrong or jump, but the sender has no part in delivering fuel. It cannot starve the engine whatever the fuel level.
D. A worn pump delivers low volume whenever it runs, so it would have failed the volume test at half a tank and would also show under hard acceleration with a full tank. This fault is tied to low fuel level and cornering only.
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On a port-injected engine, cylinder 3 runs lean while the other cylinders are normal. Any of these could be the cause EXCEPT:
- a cylinder 3 injector partly clogged with deposits.
- low rail pressure from a weak fuel pump.
- a leaking lower O-ring on the cylinder 3 injector.
- high resistance in the cylinder 3 injector connector.
Show the answer
B. Correct. All the injectors share one rail, so low pressure from a weak pump would lean every cylinder, not cylinder 3 alone. A single lean cylinder points to something affecting that cylinder only: its injector, its injector circuit or an air leak at its port.
Why not the others
A. This could cause it. Deposits on the injector's tip or inlet filter cut its flow, so cylinder 3 gets less fuel than the PCM commands while the others are normal.
C. This could cause it. The lower O-ring seals the injector into the intake manifold; a leak there lets unmetered air into cylinder 3's port, leaning that cylinder alone.
D. This could cause it. Resistance in the connector cuts the current through the injector winding, so it opens slowly or not fully and delivers less fuel in each pulse.
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A high-mileage fleet van with a PCV valve has oil-soaked residue in the air filter housing where the crankcase breather hose connects, and oil seeping from the valve cover gaskets. Compression and cylinder leakage are within the manufacturer's specifications. Which of these could be the cause?
- A vacuum leak at the intake manifold gasket
- A PCV valve stuck in the open position
- A PCV valve stuck in the closed position
- A breather hose off at the air filter housing
Show the answer
C. Correct. With the PCV valve stuck closed, blowby cannot be drawn into the intake, so crankcase pressure rises and pushes oily vapor backward through the breather hose into the air filter housing and out past the gaskets. Normal compression and leakage show the blowby itself is not excessive; the valve is replaced and the hoses checked.
Why not the others
A. An intake gasket leak lets unmetered air into the engine and causes a lean, rough idle, but it does nothing to raise crankcase pressure. Oil pushed back into the air filter housing means crankcase vapor has no way out through the PCV valve.
B. A valve stuck open draws more crankcase vapor into the intake, which holds the crankcase under vacuum and pulls fresh air in through the breather hose, not oil out of it. It shows up as a lean or high idle instead.
D. With the breather hose off at the housing, crankcase vapor would escape from the loose hose end into the engine compartment rather than into the housing. Oil inside the housing means vapor is being forced through a connected hose by crankcase pressure.
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Any of these can shorten the life of a catalytic converter EXCEPT:
- a misfire sending unburned fuel into the converter.
- a downstream oxygen sensor that responds slowly.
- oil burned in the cylinders past worn valve stem seals.
- a converter shell dented by a hard road strike.
Show the answer
B. Correct. The downstream sensor watches the gas leaving the converter so the PCM can judge its efficiency; a slow response can upset that judgment or set a sensor DTC, but it puts nothing into the exhaust that harms the converter.
Why not the others
A. This can. Unburned fuel from a misfiring cylinder burns inside the converter, and the heat can melt or crack the substrate; misfires are repaired before a converter is replaced.
C. This can. Oil burned in the cylinders leaves ash and additive deposits, such as phosphorus, that coat the catalyst and cut its efficiency over time.
D. This can. The ceramic substrate inside the shell is brittle, so a hard impact can crack it or break it loose; loose pieces rattle, break up further and can restrict the exhaust.
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A generic OBD II scan tool shows no DTCs, yet the ABS warning lamp is on. Why might the tool show no ABS code?
- The ABS module erases its codes at every key-off
- ABS faults turn on the lamp without storing codes
- Generic access covers emission-related data only
- ABS codes are read only after the MIL also comes on
Show the answer
C. Correct. OBD II requires standardized access to emission-related powertrain data, and that is what a generic scan tool reads. Codes in the ABS, air bag and body modules are read with a scan tool that has enhanced, manufacturer-specific coverage.
Why not the others
A. Key-off does not erase an ABS module's DTCs; they are kept until cleared or until the module's own rules erase them. The generic tool simply cannot reach that module's codes.
B. An ABS module that detects a fault and turns its lamp on stores a DTC for it. The code is there but outside what generic OBD II access reads.
D. The MIL reports emission faults and has nothing to do with reading ABS codes. ABS codes are read from the ABS module with an enhanced scan tool.
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On a batch-fired engine, one PCM driver grounds two injectors wired in parallel. Each injector winding measures 12.0 ohms, and system voltage is 13.5 volts. Ignoring wiring resistance, how much current does the driver carry while both injectors are on?
- 0.56 A
- 1.13 A
- 2.00 A
- 2.25 A
Show the answer
D. Correct. Two equal 12.0-ohm windings in parallel give 12.0 / 2 = 6.0 ohms, and 13.5 V / 6.0 ohms = 2.25 A. The driver must handle the sum of both injectors' current, which is why a shorted injector on a shared driver can damage it.
Why not the others
A. This treats the two windings as if they were in series: 13.5 V / (12.0 + 12.0) ohms = 0.56 A. In parallel the combined resistance is 6.0 ohms, so the driver carries 2.25 A.
B. This is the current through one injector only: 13.5 V / 12.0 ohms = 1.13 A. The driver carries both injectors' current, 2.25 A.
C. This uses a nominal 12 volts instead of the 13.5 volts stated: 12 V / 6.0 ohms = 2.00 A. With 13.5 volts the current is 2.25 A.
03Answer key
| Question | Answer | Content area |
|---|---|---|
| Q1 | C | General Diagnosis |
| Q2 | C | General Diagnosis |
| Q3 | D | Ignition System Diagnosis and Repair |
| Q4 | B | Ignition System Diagnosis and Repair |
| Q5 | A | Fuel, Air Induction and Exhaust Systems Diagnosis and Repair |
| Q6 | B | Fuel, Air Induction and Exhaust Systems Diagnosis and Repair |
| Q7 | C | Emissions Control Systems Diagnosis and Repair |
| Q8 | B | Emissions Control Systems Diagnosis and Repair |
| Q9 | C | Computerized Engine Controls Diagnosis and Repair |
| Q10 | D | Computerized Engine Controls Diagnosis and Repair |
04Questions by content area
Working on one part of the A8 test? Each content area has its own page with five more free questions.
05More free questions
The A8 study guide covers each content area and how to study for it, and the ASE A8 Engine Performance practice test page describes the full A8 question bank. The same free format is available for the other eight tests.
How these questions are written and checked: how our questions are made. Found a mistake? Tell us and we will fix it.
ToolboxPrep is an independent study site. It is not affiliated with or endorsed by ASE (the National Institute for Automotive Service Excellence). Our questions are original practice questions written to the published ASE test specifications; they are not actual test questions.