EXCELLENCE AUTO TECH • ARTICLE 20 • PART 1
Automotive Ignition Systems: From Contact Points to the Hall Sensor
Physical fundamentals, ignition advance, coils, distributor, sensors and technological evolution.
Learning objectives
By the end of this first part, you should be able to explain how the spark is produced, distinguish the main types of ignition, understand advance and dwell, recognize the function of each component and choose suitable tests for mechanical and electronic systems.
Safety: high voltage and electronic components
Ignition can produce tens of thousands of volts. Never hold energized leads, plugs or coils, and never create sparks with loose wires near fuel or flammable vapors.
Use proper testers, insulated tools and the manufacturer’s procedures. Before disconnecting modules, coils or sensors, check the method for that application. Do not apply voltage directly to signal or command terminals.
1. The mission of the ignition system
In spark-ignition engines — such as those running on gasoline, ethanol and many flex-fuel engines — the air-fuel mixture must start burning at a controlled instant. The spark plug creates the electrical discharge that starts a flame front. Combustion releases heat, raises cylinder pressure and helps produce torque at the crankshaft.
The system must meet three conditions at the same time: a spark with enough energy, in the right cylinder and at the right moment. If any of them fails, hard starting, loss of power, high consumption, misfires or even damage to the engine and catalytic converter can result.
Diagram 1 — Functional path of the ignition
The primary can be controlled by contact points, a power module or electronic circuits commanded by the ECU. High-voltage distribution depends on the system architecture.
2. How the coil turns energy into a spark
The battery supplies low-voltage electrical energy. The coil has a primary winding, a secondary winding and a magnetic circuit. When current flows through the primary, a magnetic field forms and stores energy.
In conventional inductive systems, the circuit rapidly interrupts the primary current. The change in magnetic flux induces a high voltage in the secondary. When the available voltage exceeds what is needed to break down the gap between the electrodes, the spark occurs.
The coil does not produce high voltage simply by receiving 12 V. It is the dynamics of the magnetic field, the electrical command and the secondary load that determine the process.
Diagram 2 — Simplified inductive coil cycle
2.1 Available voltage is not required voltage
The coil has a capacity to generate voltage, but discharge occurs when the voltage reaches what is needed to cross the gap under the present conditions. This requirement changes with cylinder pressure, mixture composition, electrode geometry and wear, and system insulation.
That is why an ignition can work well at idle and fail on a climb: under higher load, cylinder pressure tends to raise the voltage needed to start the discharge. Deteriorated leads, worn plugs and weak coils become more evident under these conditions.
2.2 Coil construction and types
The traditional cylindrical coil (called oil-filled/asphalt-type, after its internal insulation) has a metal case, a laminated iron core and two windings. The primary has a few hundred turns of thicker wire (on the order of 350) and connects to terminals 15 (positive) and 1 (command). The secondary has tens of thousands of turns of fine wire (on the order of 20,000): one end exits through terminal 4, the high-voltage output, and the other connects internally to the primary. Plasticcoils, with a compact construction, came with newer engines and electronic injection; they generally have a much lower primary resistance.
| Cylindrical coil (Bosch example) | Stated maximum voltage | Sparks per minute |
|---|---|---|
| E — 12 V (aluminum) | 24,000 V | 13,000 |
| K — 12 V (blue) | 26,000 V | 16,000 |
| KW — 12 V (red) | 28,000 a 34,000 V | 18,000 |
The rated voltage is the coil’s maximum capacity , not the voltage it works at. In normal use, the coil only generates the voltage needed to overcome the circuit’s “barriers”: compression, electrode gap, leads, rotor and cap. That is why there must be a reserve between available and required voltage; as components wear, the requirement rises and the reserve shrinks.
2.3 Testing the coil by resistance
The most complete test uses an oscilloscope with the engine running at normal temperature. Measuring resistance with an ohmmeter is simpler but less conclusive: it shows open or shorted windings, but does not reveal insulation faults that only appear under high voltage or heat. Measure with the coil at room temperature (about 20 to 30 °C), because temperature changes the result considerably.
| Coil type | Primary (terminals 15 and 1) | Secondary (terminal 4 to 15 or 1) |
|---|---|---|
| Conventional cylindrical (for contact points) | about 3 to 4 Ω | about 5 to 11 kΩ |
| High-energy cylindrical (electronic ignition) | about 0.7 to 2.2 Ω | about 3 to 11 kΩ |
| Modern plastic | about 0.5 Ω | about 8 to 13 kΩ |
Typical ranges from Bosch catalogs, for teaching reference only. The correct value depends on the part number: always consult the manufacturer’s table.
3. Ignition timing and advance
Combustion takes time to develop. Under many operating conditions, the spark must occur before top dead center (TDC) of the piston at the end of compression, so that useful pressure develops at the right moment.
This lead is the ignition advance, usually expressed in degrees of crankshaft rotation before TDC. There is no single ideal fixed advance for every situation: speed, load, temperature, fuel and control strategy all affect the value.
Diagram 3 — Combustion timeline
Programmed spark
Reversal of motion
Pressure development
Conceptual representation. The spark instant and the position of the pressure peak depend on operating conditions and engine design.
3.1 Centrifugal advance
In conventional distributors, weights and springs mechanically change when the contact points open according to engine speed. When the mechanism is seized, worn or has the wrong springs, the advance curve no longer follows the specification.
Test: with a timing light and the procedure for the vehicle, compare the base timing and how it progresses as speed rises. Check that the mark advances and returns consistently. Some systems require disconnecting the vacuum advance or a specific test condition.
3.2 Vacuum advance
A capsule with a diaphragm can move the distributor mechanism in response to the vacuum it receives. It corrects timing under certain load conditions. The response depends on how the vacuum port was designed and connected.
Test: where specified, apply controlled vacuum with a hand pump and observe diaphragm movement and retention. Also check the hose, connections and blockages. A punctured diaphragm may not hold vacuum.
3.3 Electronic advance
In electronically managed systems, the ECU calculates spark timing from maps and sensor information. It may consider speed, load, temperature and knock, among other variables. The value shown on the scan tool must be interpreted according to the strategy and documentation for the application.
Timing too retarded: can cause low power, higher consumption and higher exhaust gas temperature.
Caution: these symptoms are not exclusive to ignition timing.
3.4 Base timing on distributor systems
On engines with a distributor and electronic injection from the 1990s (“dynamic” mapped ignition), the advance is calculated by the ECU, but the distributor position sets the reference. That is why these systems require checking base timing with a timing light, putting the ECU into a fixed-advance mode. Each system has its own method:
| System (examples) | How to fix the advance | Typical timing cited |
|---|---|---|
| Le-Jetronic without EZK (Monza up to 1991) | disconnect the vacuum advance; idle ~900 rpm | 8° BTDC |
| Multec 700 TBI (GM) | bridge terminals A and B of the ALDL connector; 2,000 rpm | 10° BTDC |
| EEC-IV (Autolatina) | remove the shorting plug with the engine idling | 6° to 9° BTDC, depending on the model |
| VW 1AVB, 1AVP, 1AVS, MP 9.0 (1997 onwards) | procedure with the shorting plug depending on the system | 6° to 9° BTDC, depending on the engine |
4. Contact-point ignition: the classic system
The conventional system uses a battery, ignition switch, coil, contact points, condenser, distributor, rotor, cap, leads and spark plugs. In certain applications there is also a resistor or resistive wire in the primary circuit.
The distributor cam opens and closes the contact points. With the contacts closed, current flows through the primary. When they open, the current is interrupted and the coil produces high voltage, which passes through the rotor and cap to the lead for the corresponding cylinder.
Diagram 4 — Distributor with contact points
Move the contact
Interrupt the primary
Controls transients and arcing
Distribute high voltage
The advance mechanisms and the condition of the shaft bushings also affect spark timing.
4.1 Dwell: coil charging time
The dwell is the period during which the primary circuit conducts current. In contact-point distributors, it is usually expressed in degrees of distributor rotation.
Insufficient dwell: the coil may store little energy, especially at high speed. Excessive dwell: can increase heat dissipation and harm contacts and coil, depending on the circuit design.
Setting only the visual opening of the contacts does not replace checking dwell when the procedure calls for that instrument. Changing the contact point gap can also change ignition timing; that is why the adjustment sequence matters.
4.2 The role of the condenser
The condenser, connected to the contact point circuit, reduces heavy arcing across the contacts and affects how quickly the current is interrupted. When it is faulty or has unsuitable characteristics, accelerated contact wear, misfires and reduced ignition energy can occur.
Workshop case: the mechanic replaces the contact points and, a few days later, finds the contacts burned again. Instead of repeating the replacement, they should investigate the condenser, primary current, coil compatibility, the resistive circuit where present and the adjustment.
4.3 Distributor shaft play
Worn bushings allow the shaft to move sideways and can change the contact point opening on each revolution. The results include unstable dwell, timing variation and rough idle. With the engine off, check for excessive play according to the technical procedure. With the engine running, a timing light can help identify instability, but a wandering mark also requires investigating other causes.
4.4 Cap, rotor and leads
Look for cracks, moisture, carbon tracking, oxidation, deteriorated terminals and signs of high-voltage leakage. Worsening on damp days may indicate loss of insulation, but does not on its own confirm which component is faulty.
For resistive leads, resistance measurements are only meaningful when compared with the construction and specification of that lead. Do not use a universal limit to condemn every model.
4.5 Rotor and suppressor leads: reference values
The rotor and leads do not just carry high voltage: they also contain a suppressor resistor, which reduces the electromagnetic interference generated by the spark. Without it, the interference can disturb the radio, the injection ECU and other modules.
Leads come in two types. With a suppressor terminal (TS), the resistor sits inside the terminals and its value is usually printed on them. With a suppressor cable (CS), the resistance is distributed along the conductor and increases with length; the reference cited in Brazilian standard NBR 6880 is 6 to 10 kΩ per meter. Resistance above specification forces the coil to generate more voltage and reduces the ignition reserve.
Rotors also vary: there are models with a resistor of about 1 kΩ and others of 4 to 6 kΩ, as well as differences in material (Bakelite in contact-point systems, epoxy in electronic systems). Because caps and rotors from different systems can look identical, replacement must follow the application catalog. Also: the greater the distance between the rotor tip and the cap terminal (due to wear), the higher the required voltage.
5. From mechanical to electronic ignition
The main limitation of contact points is the need for physical contact and periodic adjustment. Electronic systems began detecting position and speed with sensors and controlling coil current with power transistors.
This does not mean every vehicle with an electronic sensor immediately did away with the distributor. There were intermediate architectures with a sensor and electronic module, but still with a rotor and cap distributing the high voltage.
Simplified evolution
6. Hall sensor: position turned into an electrical signal
The Hall sensor uses an element sensitive to magnetic fields and an electronic circuit to produce a signal associated with the passage of a window, vane or magnetic element. Common configurations have supply, ground and signal.
Its signal is often digital, switching between electrical levels defined by the circuit. However, supply voltage, output levels and terminal configuration are not universal. Hall sensors can also have architectures other than three wires.
Diagram 5 — Conceptual Hall signal
Teaching illustration of high and low levels; it does not represent a real measurement or define voltages or timing.
6.1 How to test the Hall sensor
- Identify the terminals using the correct wiring diagram.
- Check supply and ground, preferably under the conditions in which the fault occurs.
- Confirm that the reference element moves correctly.
- Observe the signal while cranking with a suitable instrument; the oscilloscope makes it possible to analyze pulses, dropouts and regularity.
- If there is no signal, investigate the circuit, connector, mechanical reference and sensor before replacing the part.
Measuring the resistance of a Hall sensor as if it were an inductive coil is generally not a conclusive test and may be inappropriate.
7. Inductive sensor and CKP sensor
The CKP reports crankshaft position and speed. It is a function in the system, not a single type of construction: there are inductive, Hall and other CKP technologies.
In a passive inductive pickup, the passage of the reference wheel teeth changes the magnetic flux and induces an alternating voltage. The frequency follows engine speed and the amplitude generally grows with speed, although it also depends on the air gap, wheel design and circuit.
The passive inductive sensor normally needs no external supply to generate its signal. Depending on the application, resistance measurement, AC voltage while cranking and waveform analysis can be useful. None of them should be interpreted without specification and context.
Diagram 6 — Inductive pickup and tone wheel
sensor
field
↔
The clearance between sensor and wheel must follow the specification. Damaged teeth, misalignment and interference can compromise the signal.
7.1 Hall and inductive: technical comparison
| Criterion | Typical Hall | Passive inductive |
|---|---|---|
| Supply | Usually external | Generates its own signal |
| Output | Usually digital pulses | Alternating voltage |
| Slow cranking | Can keep defined levels | Amplitude tends to be lower |
| Diagnosis | Supply, ground and pulses | AC signal, waveform and circuit |
8. CMP sensor and synchronization
The CMP reports the position or phase of the camshaft. Combined with the CKP, it lets the ECU identify the relationship between crankshaft and camshaft and recognize the phase of the cylinders’ cycle.
These signals can support sequential injection, ignition synchronization and variable valve timing strategies, depending on the engine. A CMP fault can cause slow starting, loss of functions or limp-home mode, but does not always stop the engine from running.
A CKP/CMP correlation fault code can originate in the sensor, harness, reference wheel or mechanical timing. Replacing the sensor without checking the correlation between signals may leave the real cause untouched.
9. Distributorless ignition, wasted spark and COP
9.1 Wasted spark system
In some architectures, one coil serves two spark plugs at the same time. One spark occurs in the cylinder on compression and the other in a cylinder on the exhaust stroke, where there is no compressed mixture to ignite. Hence the name wasted spark.
Cylinder pairs depend on the engine architecture. Do not assume a pairing without consulting the diagram.
Diagram 7 — One coil, two plugs
Compression
Dual
Exhaust
The diagram shows the function; the electrical connection and spark polarity depend on the design.
9.2 COP system — Coil On Plug
In the COP configuration, the coil sits directly on the spark plug or very close to it. The system eliminates the distributor and reduces the need for long high-voltage leads in many applications.
Some coils contain only the transformer and are commanded by an external module. Others integrate driver electronics. The test method must respect this difference: a logic command terminal must not be treated as if it were the negative of a conventional coil.
Plug 1
Plug 2
Plug 3
Plug 4
9.3 CDI — capacitive discharge ignition
CDI uses energy stored in a capacitor, discharged rapidly into the ignition circuit. It is a different architecture from conventional inductive ignition and appears in certain applications. Its presence does not eliminate the spark plug and does not justify applying the same tests as for an inductive coil without consulting the documentation.
Summary of Part 1
The evolution of ignition changed the command and distribution components, but not the goal: to deliver a suitable spark, in the right cylinder and at the right instant. To diagnose, it is essential to first identify the system architecture and understand how the primary, the sensors and the secondary interact.
EXCELLENCE AUTO TECH • ARTICLE 20 • PART 2
Ignition Systems: Tests, Diagnosis and Workshop Cases
Spark plugs, knock, pre-ignition, oscilloscope, intermittent faults, flowcharts and exercises.
10. Spark plugs: the last link in the system
The spark plug receives the high voltage and creates the electrical discharge between its electrodes. It works exposed to intense cycles of temperature, pressure, vibration and combustion products.
Even when the coil and sensors are working, an unsuitable, worn, fouled plug or one with compromised insulation can cause misfires.
10.1 Gap: distance between the electrodes
The gap is the distance the discharge must cross. When it is too large, the required voltage tends to increase. This can expose limitations of coils, leads and insulators, especially under load.
An improperly small gap can also change the characteristics of the discharge and the initial ignition of the mixture. The correct value depends on the plug and the engine. On some plug types, the manufacturer does not recommend readjusting the electrodes.
Diagram 8 — Spark plug discharge area
Simplified representation: the spark crosses the space between the center electrode and the ground electrode.
10.2 Heat range
The heat range describes the plug’s ability to transfer heat from its tip to the cylinder head. A plug considered hotter retains more heat at the firing end; a colder one transfers heat more efficiently.
This does not indicate spark power. The wrong choice can encourage deposits or overheating, depending on conditions. The heat range scale is also not identical across all brands.
The spark plug works well in a range of roughly 450 °C to 850 °C. Below it, carbon and oil deposits do not burn off and the plug fouls; above it, the tip can become a source of pre-ignition. Heat range numbering is not the same across brands: at NGK, a lower number means a hotter plug; at Bosch, a lower number means a colder plug. So never convert a plug by its number; use the manufacturer’s cross-reference table.
| Engine condition | Typical effect on the plug |
|---|---|
| Timing too advanced | overheating, knock, risk of pre-ignition |
| Timing retarded | carbon fouling |
| Rich mixture | carbon fouling |
| Lean mixture | overheating |
| Increased compression ratio (skimmed head) | overheating and knock |
| Low compression (rings, valves, gasket) | dry or wet carbon fouling |
| Gasoline-engine plug used in an ethanol engine (hotter) | overheating, pre-ignition and even a holed piston |
| Ethanol-engine plug used in a gasoline engine (colder) | carbon fouling |
10.3 Tightening the spark plug
Tightening depends on the seat type and the cylinder head material. The spark plug manufacturer’s general rule is: flat seat with gasket — new plug, finger-tight then about ½ turn; reused plug, about 1/12 to 1/8 turn (30° to 45°). Tapered seat, no gasket — about 1/16 turn (22.5°), new or reused. In aluminum heads, the maximum torque is lower than in cast iron. Overtightening damages the head thread; undertightening impairs heat transfer and can overheat the plug.
10.4 Reading spark plugs visually
The plug’s appearance is a diagnostic clue, not a definitive verdict. The reading depends on the running history, the fuel, the temperature and the conditions in which the engine was switched off.
Investigate a rich mixture, weak ignition, low-temperature use or an unsuitable plug.
May suggest oil entering the chamber; check mechanical condition and other causes.
Can widen the gap and increase the system’s electrical demand.
Investigate plug application, mixture, cooling, timing and abnormal combustion.
11. Knock and pre-ignition: don’t confuse them
11.1 Knock
In normal combustion, the spark starts a flame front that spreads through the mixture. In knock, part of the unburned mixture undergoes rapid autoignition, producing pressure oscillations. The driver may hear the noise known as “pinging”.
Associated factors include unsuitable fuel, excessive advance for the condition, high temperatures and the characteristics of the charge and mixture.
The knock sensor lets the ECU identify vibrations related to the phenomenon and adjust the ignition strategy, where provided. This does not mean the sensor can prevent every episode or compensate for any mechanical defect.
In systems such as the 1990s VW and Ford engines with distributor and injection, the ECU controls knock cylinder by cylinder and can retard timing by up to about 15° on the affected cylinder. On these engines, the knock sensor must be fitted at the specified torque (20 N·m on the engines cited), without washers and in the correct position: a loose or badly mounted sensor does not “hear” the knock, and the engine can be damaged.
11.2 Pre-ignition
In pre-ignition, the mixture starts burning before the commanded spark, for example because of an excessively hot spot in the chamber. Overheated deposits, components at abnormal temperature and unsuitable plugs can contribute.
Knock and pre-ignition are different phenomena and may be related in certain situations. Pre-ignition can produce dangerous pressures and temperatures, requiring immediate investigation.
Knock: abnormal autoignition of the remaining mixture during combustion started by the plug.
Pre-ignition: combustion starting before the programmed spark.
12. Professional diagnostic method
A misfire can have an electrical, electronic, mechanical or fuel-system origin. The goal of diagnosis is to prove the cause, not to pick the best-known part.
The sequence recommended by the material is:
12.1 First: characterize the symptom
Record when the fault occurs: engine cold or hot, idle, acceleration, uphill, humidity, starting or a particular speed range. Ask whether there was recent maintenance, parts replacement, engine washing or a change of fuel.
Then confirm that the engine cranks normally. If it does not crank, the initial diagnosis is different from that of an engine that cranks but does not start.
12.2 Flowchart: engine cranks but does not start
Diagram 9 — Investigation guide
If there is a spark, the investigation continues: ignition quality and timing, fuel, compression, timing and other conditions needed for running. The presence of a spark does not on its own prove the whole ignition is correct.
12.3 The scan tool shows 0 rpm while cranking
If the crankshaft physically turns and the scan tool shows 0 rpm, it is important to investigate the speed information received or displayed by the system. This may involve the CKP, tone wheel, harness, connectors, supply where applicable, ECU or even the tool’s data refresh limitations.
Do not automatically conclude that the CKP is dead. Confirm the signal with an oscilloscope and interpret the information according to the vehicle’s architecture.
13. Tools and what each one proves
| Tool | Main application | Limitation |
|---|---|---|
| Multimeter | Voltage, resistance, continuity and voltage drops | May not capture fast pulses or intermittent faults |
| Scan tool | DTCs, speed, advance and misfire counters when available | A code alone does not identify the faulty part |
| Oscilloscope | CKP/CMP pulses, Hall, command and synchronization | Requires correct connection and interpretation |
| Timing light | Timing and advance on compatible systems | Not every modern system allows the same reading |
| Ignition tester | Controlled spark check according to procedure | Does not replace all tests under real load |
13.1 What to look for on the oscilloscope
On Hall sensors, observe levels, frequency, regularity and possible dropouts. On inductive sensors, examine amplitude, polarity, pulse spacing and reference wheel patterns. When comparing CKP/CMP, check whether the timing relationship matches the engine’s technical reference.
In ignition primary circuits, the waveform can give clues about charging, current interruption and coil behavior. However, interpretation depends on the type of drive. Never connect an ordinary oscilloscope channel directly to high voltage without a suitable, properly rated accessory.
14. Workshop case studies
Case 1 — Engine misfires when hot and runs again when cold
Report: after a few minutes running, the engine starts misfiring, stalls and only restarts after cooling down.
Hypotheses: coil, module, CKP, connections and supply with a temperature-sensitive fault, as well as causes unrelated to ignition.
Procedure: reproduce the symptom safely and record supply, command and signals while the fault is present. If tests are only done after the assembly cools, the abnormality may disappear.
Lesson: measuring while the fault is happening is more useful than replacing parts on suspicion.
Case 2 — Misfire when accelerating or climbing a hill
Report: idle apparently normal, but the engine misfires under load.
Hypotheses: worn plug, wrong gap, high-voltage leakage, weak coil or a fuel supply problem.
Procedure: inspect plugs, insulators, leads and coils; check electrical conditions and, when possible, reproduce the fault with appropriate instruments. Do not blame the symptom exclusively on the ignition.
Case 3 — Misfire code on cylinder 2
Report: the scan tool records a misfire on cylinder 2 of an engine with interchangeable COP coils.
Procedure: if the manufacturer allows it and the coils are truly compatible, move the coil from cylinder 2 to another cylinder, record the conditions and repeat the test.
Interpretation: if the misfire follows the coil, the evidence against it grows stronger. If it stays on the original cylinder, investigate the plug, injector, electrical command, compression, air leaks and other causes.
Caution: do not swap coils when there are application differences, risk of damage, access restrictions or a contrary manufacturer procedure.
Case 4 — Contact points burn repeatedly
Report: new contacts show severe wear after a short time.
Procedure: check the condenser, primary current and configuration, coil compatibility, any resistor, dwell and the distributor’s mechanical condition.
Lesson: the damaged component may be the consequence of another fault.
Case 5 — CKP/CMP synchronization code
Report: long cranking, loss of performance and a correlation code between sensors.
Procedure: check electrical signals, supply where applicable, connectors and the relationship between the waveforms. When indicated, check mechanical camshaft timing and the integrity of the reference wheels.
Lesson: a correlation fault does not necessarily mean a faulty sensor.
15. Quick matrix: symptom, hypothesis and first test
Check spark, supply, command, recognized speed and general running conditions.
Reproduce the condition and measure signals and supply during the fault.
Inspect plugs, gap, coils, leads and fuel supply.
Check shaft, cam, advance, drive and dwell.
Investigate insulation, cap, rotor, leads, coils and connectors.
Investigate advance, fuel, temperature and abnormal combustion.
Check speed recognition and the CKP circuit, without automatic condemnation.
16. Checklist before condemning a part
☐ I correctly identified the vehicle, engine and ignition architecture.
☐ I confirmed the symptom and the conditions in which it occurs.
☐ I consulted the wiring diagram and the application’s specifications.
☐ I checked supply, ground and connectors.
☐ I analyzed the command and relevant signals.
☐ I inspected plugs, coils and high-voltage components.
☐ I considered fuel, compression and mechanical timing.
☐ I have measurable evidence of the probable cause.
☐ I repeated the test after the repair and recorded the result.
17. Practice exercises — 10 questions
Choose one answer per question. The exercises are for teaching and do not reproduce the app’s protected assessment bank.
1. A vehicle with contact points shows burned contacts a few days after replacement. What is the most appropriate action?
A) Replace the contact points again without testing.
B) Check the condenser, dwell and primary circuit.
C) Increase the spark plug gap.
D) Necessarily replace the rotor.
2. An engine cranks but has no spark. What is a logical first step?
A) Replace all spark plugs immediately.
B) Increase the advance without measuring.
C) Check ignition supply, ground and command.
D) Replace the ECU without checking signals.
3. A fault occurs only with the engine hot. Which approach is most likely to reveal its cause?
A) Measure only after it cools down.
B) Reproduce the fault and measure while it is happening.
C) Replace the coil without testing.
D) Ignore the fault if there is no code.
4. What is the main function of the CKP sensor?
A) To measure spark plug temperature.
B) To report crankshaft position and speed.
C) To mechanically adjust the contact points.
D) To measure fuel pressure.
5. A typical Hall sensor shows no signal. What should be checked before condemning it?
A) Supply, ground and the reference element.
B) Only resistance, as with any inductive sensor.
C) Only the heat range of the plugs.
D) Only the tire pressure.
6. In a conventional contact-point system, dwell relates to what?
A) The time the primary circuit conducts current.
B) The distance between the plug electrodes.
C) The catalytic converter temperature.
D) Intake manifold pressure.
7. In a wasted-spark system, the simultaneous firing normally occurs:
A) In two cylinders always on compression.
B) In one plug on compression and another on exhaust.
C) Only in the cylinder without fuel.
D) Only when there is knock.
8. A misfire follows a COP coil after a controlled, permitted swap between cylinders. What does this indicate?
A) That the moved coil is a strong suspect.
B) That the CKP is necessarily faulty.
C) That compression is low in all cylinders.
D) That there is no need to confirm the result.
9. Which statement correctly distinguishes knock and pre-ignition?
A) They are exactly the same phenomenon.
B) Pre-ignition always occurs after the spark.
C) Knock involves abnormal autoignition of the remaining mixture; pre-ignition starts before the programmed spark.
D) Knock is caused only by a worn plug.
10. Does a CMP-related fault code prove that the sensor is damaged?
A) Yes, on all vehicles.
B) Yes, as long as the battery is charged.
C) No; the circuit, signal, reference and timing must be checked.
D) No; the CMP never affects operation.
Answer key with comments
1 — B. Repeated wear may be the consequence of a fault in the condenser or primary circuit.
2 — C. Without supply or command, the coil should not be condemned.
3 — B. Thermal faults may disappear after cooling.
4 — B. The CKP provides crankshaft position and speed information.
5 — A. The sensor must be assessed within its circuit and mechanical reference.
6 — A. Dwell is linked to the conduction period and coil charging.
7 — B. One spark is useful and the other occurs on the exhaust stroke.
8 — A. The misfire moving with the coil strengthens suspicion of that coil.
9 — C. The phenomena have different mechanisms and starting moments.
10 — C. Codes indicate detected abnormalities, not an automatically condemned part.
18. Workshop technical glossary
| Portuguese | Technical English |
|---|---|
| Ignition coil | Ignition coil |
| Contact points | Breaker points |
| Distribuidor | Distributor |
| Condenser | Condenser / capacitor |
| Sensor de rotação | Crankshaft position sensor |
| Sensor de fase | Camshaft position sensor |
| Avanço de ignição | Ignition timing advance |
| Falha de combustão | Misfire |
| Roda fônica | Reluctor / tone wheel |
| Chicote elétrico | Wiring harness |
19. Conclusion: diagnosing means demonstrating the cause
The ignition system evolved from contact points and the mechanical distributor to electronic sensors, power modules, dual coils and individual coils. The technology changed, but the basic logic remains: energy must reach the right plug, at the right instant and in condition to start combustion.
The professional who understands this logic does not rely only on fault codes or trial-and-error replacements. They observe the symptom, identify the circuit, measure the relevant quantities and confirm the repair.
The question that guides diagnosis
“What should be happening in this circuit — and which measurement shows that it isn’t?”
Editorial note: this content is general teaching material. Procedures, terminal identification, electrical values, advance, dwell, gaps and component installation must follow the manufacturer’s technical documentation for the corresponding vehicle and market.