ASE A8 ignition systems practice questions.

Five free practice questions on ignition systems: content area B of the ASE A8 Engine Performance test, 8 of its 50 scored questions (16%). They are in the ASE format: four options, one best answer. Answer each one before opening the explanation. No account, no email.

01The questions

1. EXCEPT · Ignition System Diagnosis and Repair

   A two-wire coil-on-plug coil is fed battery voltage and switched to ground by a PCM driver that watches its control circuit for an open or a short, and an ignition coil control circuit DTC is stored for that coil. Any of these could set the DTC EXCEPT:

   1. a spark plug gap worn far wider than specified.
   2. the control wire shorted to ground in the harness.
   3. an open primary winding in the coil.
   4. an open in the wire feeding the coil's power terminal.
   Show the answer

   A. Correct. A worn-wide gap raises the voltage the secondary must make, but the primary circuit stays electrically complete, so the driver sees a normal circuit and no control circuit DTC sets; a resulting misfire is caught by the misfire monitor instead. A control circuit DTC points to the wiring, the coil's primary or the driver.

   Why not the others

   B. This could set it: with the control wire shorted to ground, the coil is energized whenever its feed is live and the PCM cannot switch it off, so the driver sees the circuit low when it should be high and flags a fault.

   C. This could set it: an open primary leaves the driver's terminal with no voltage from the feed when the driver is off and no current when it is on, which the PCM reads as an open control circuit.

   D. This could set it: with the feed open, no voltage reaches the control wire through the coil, so the driver sees the same open circuit that a broken winding or control wire would give.

2. Recall · Ignition System Diagnosis and Repair

   On an engine with spark plug wires, the manufacturer's routing holds the wires in separators and apart from one another. Why?

   1. To make the plugs fire in the engine's firing order
   2. To keep each wire's resistance within its limit
   3. To stop one wire inducing a spark in another
   4. To shield the wires from the vehicle's radio noise
   Show the answer

   C. Correct. A firing wire's high-voltage pulse can induce voltage in a wire running close beside it, and where the two cylinders fire one after the other that can fire the wrong plug (crossfire), causing misfire or spark knock. The routing also keeps the wires clear of hot exhaust parts.

   Why not the others

   A. The firing order is set by the PCM or distributor and by which wire goes to which plug, not by the separators. They keep wires apart so one cannot induce a spark in another.

   B. Resistance depends on the wire's conductor and length, not on how it is routed beside other wires. The separators prevent induced crossfire between wires and keep them off hot parts.

   D. The plug wires are a source of electrical noise rather than a victim of it, and resistance-type conductors suppress it. Separators keep the wires apart to prevent induced crossfire.

3. Spec reading · Ignition System Diagnosis and Repair

   An engine misfires only under hard acceleration. The spark plugs, at 98,000 miles, are removed and measured: the manufacturer's gap specification is 0.040 to 0.044 in., and the plugs measure 0.062 to 0.066 in. What do these measurements indicate?

   1. The gaps are worn wide and need more voltage under load
   2. The gaps are too narrow to light the mixture under load
   3. The gaps are within spec, so the plugs are not the cause
   4. The gaps are worn wide, so they need less voltage to fire
   Show the answer

   A. Correct. At 0.062 to 0.066 in. the gaps are 0.018 to 0.022 in. over the 0.044 in. maximum. The voltage a gap needs rises with its width and with cylinder pressure, so worn gaps demand the most under hard acceleration, where the coil may fall short; the plugs are replaced.

   Why not the others

   B. The measured gaps are larger than the specification, not smaller; reading them as narrow reverses the comparison. Wide gaps raise the voltage the coil must supply.

   C. Every plug is above the 0.044 in. maximum, by 0.018 to 0.022 in., so none is within the specification. The gaps have worn wide.

   D. A wider gap needs more voltage to break down, not less, and the demand rises further with cylinder pressure under hard acceleration, which is exactly when this engine misfires. The worn plugs are replaced.

4. Recall · Ignition System Diagnosis and Repair

   How does a piezoelectric knock sensor produce its signal?

   1. Vibration changes its resistance on a reference
   2. Vibration stresses a crystal that makes voltage
   3. A toothed wheel varies the field around a magnet
   4. A Hall element switches a supplied voltage
   Show the answer

   B. Correct. The sensor's piezoelectric element produces a small voltage when it is stressed, so the vibration of detonation passed through the block makes an AC signal. The PCM looks for that signal in the knock frequency band and retards spark timing when it appears.

   Why not the others

   A. Varying resistance on a reference voltage is how a thermistor or potentiometer works. A piezoelectric sensor generates its own voltage when vibration stresses its crystal.

   C. That describes a magnetic (variable reluctance) speed or position sensor. A knock sensor mounts on the engine and generates voltage from vibration acting on a piezoelectric crystal.

   D. Switching a supplied voltage is how a Hall-effect position sensor works. A knock sensor needs no switching element; its piezoelectric crystal generates voltage when vibration stresses it.

5. Recall · Ignition System Diagnosis and Repair

   When a replacement PCM is being programmed, the programming software asks the technician to enter or confirm the vehicle identification number (VIN). Why?

   1. To copy the learned fuel trims from the old PCM
   2. To select the calibration for that vehicle's build
   3. To unlock the scan tool's access to live data
   4. To clear readiness monitors before the drive cycle
   Show the answer

   B. Correct. One PCM part can serve many engines, transmissions and emissions packages, and the VIN tells the programming system which calibration matches this vehicle. A wrong calibration can cause driveability complaints and DTCs, and the VIN is stored in the new PCM, where a scan tool can read it back.

   Why not the others

   A. Learned values such as fuel trim stay in the old PCM's memory and are not moved by entering a VIN; the new PCM relearns them as the vehicle is driven. The VIN selects the calibration.

   C. A scan tool reads live data from an installed PCM without the VIN being entered. The VIN is asked for so the correct calibration is loaded for this vehicle.

   D. Programming does leave the monitors incomplete, but that follows from the new memory, not from the VIN. The VIN is entered so the software loads the calibration for this vehicle's build.

02Answer key

03What area B covers

This content area covers ignition systems from the primary circuit to the spark plug: coil-on-plug and waste-spark coils, plug wires and boots, spark plugs with their gaps and heat ranges, crankshaft and camshaft position sensors, knock sensors, ignition control modules and the PCM, misfire and coil DTCs, and the scope and meter tests that separate one failed part from another.

The ASE test specification calls this content area “Ignition System Diagnosis and Repair”. It carries 8 of the 50 scored questions, 16% of the test.

• Diagnose no-start, misfire, knock and power loss
• Interpret misfire and coil circuit DTCs
• Test primary circuit feeds, grounds and drivers
• Inspect plugs, wires, boots and secondary circuits
• Test coils with a scope, current probe or ohmmeter
• Test crankshaft, camshaft and knock sensors
• Replace and program ignition modules and PCMs

04What the questions turn on

Swap the coil, follow the misfire

On a coil-on-plug engine, two coils are swapped between cylinders, the codes cleared and the engine run under the same conditions. If the misfire moves with a coil, that coil's winding or boot is breaking down and the coil is replaced.

Firing line and spark line

The firing line shows the voltage needed to push current across the whole secondary path. Added resistance, such as a burned boot contact, raises it and leaves a shorter spark line. A worn-wide plug gap also needs more voltage.

Control circuit DTC or misfire

A coil control circuit DTC comes from the PCM driver seeing a fault in the primary circuit, such as an open control wire. A worn plug gap leaves the primary complete, so it sets no control circuit DTC. The misfire monitor catches it instead.

Magnetic versus Hall-effect sensors

A magnetic sensor makes its own AC voltage, which falls as its air gap widens, so a weak signal can fail at cranking speed and pass once rpm rises. A Hall-effect sensor switches at any speed, even when the engine is turned by hand.

05The other content areas

The A8 test has five content areas. Each has its own page of free questions:

The ASE A8 Engine Performance practice test page describes the full question bank. 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.