Ignition Systems Questions and Answers

Answer: C

A tip that never reaches its self cleaning temperature accumulates deposits and eventually shorts the spark. Pre-ignition and detonation both follow from too hot a plug, which makes those options describe the opposite error. Checking which component actually carries the load settles most questions of this kind at once. Naming what changes and what stays the same is the reliable route through questions of this shape. Reading the definition literally, rather than recalling a summary, avoids the usual confusion.

Answer: D

Below about 500 degrees the plug fouls and above about 850 it causes pre-ignition, so the working window lies between. Those figures are why heat range must match the engine and its duty. Tracing the requirement back to the physical constraint that produces it makes the answer follow. Working the distinction through on a single concrete case fixes it more firmly than any rule of thumb. Most errors here come from carrying across a result from a neighbouring case where it does not hold.

Answer: A

Light tan or grey indicates correct mixture, temperature and heat range. Black soot means rich running or a cold plug, and white blistering means overheating. Reading plugs remains a useful diagnostic skill. The shared behaviour explains why these belong together and the differences explain why both exist. A symptom that appears under one condition and not another is what narrows the diagnosis quickly. Working the distinction through on a single concrete case fixes it more firmly than any rule of thumb.

Answer: B

Blistering and a chalky white appearance mean the tip has run too hot, from lean mixture, overadvanced timing or the wrong heat range. Coolant genuinely does leave white deposits, which makes the last option a real if different diagnosis. Naming the cost of a choice alongside its benefit is what turns a fact into a design decision. The order in which the effects act is what decides the outcome, so it is worth establishing first.

Answer: C

Wet oil fouling points to worn rings, valve stem seals or a failed turbocharger seal. Ash deposits genuinely come from burnt oil additives too, which makes the last option a real related observation. Dry soot indicates rich mixture. Reading the definition literally, rather than recalling a summary, avoids the usual confusion. Checking which component actually carries the load settles most questions of this kind at once. The shared properties explain why these belong to one family, and the differences explain why more than one exists.

Answer: D

Platinum and iridium resist erosion and allow intervals beyond a hundred thousand kilometres. Copper cores genuinely conduct heat well and are used within the centre electrode, which makes the second option true of the core rather than the tip. Most errors here come from carrying across a result from a neighbouring case where it does not hold. Tracing the requirement back to the physical constraint that produces it makes the answer follow. Working one numerical case through both cases side by side fixes the distinction better than any rule of thumb.

Answer: A

Gap widens as the electrodes erode and is set with a feeler or wire gauge. Plug resistance genuinely is measurable and a failed suppressor causes misfire, which makes the second option a real if less common check. Naming what changes and what stays the same is the reliable route through questions of this shape. The shared behaviour explains why these belong together and the differences explain why both exist. Reading the definition literally, rather than recalling a formula, is the reliable route through questions of this shape.

Answer: B

Levering against the fine centre electrode snaps it off, so only the earth electrode is moved, and many such plugs are preset. Wire gauges genuinely are preferred for fine electrodes, which makes the last option sound advice. Working the distinction through on a single concrete case fixes it more firmly than any rule of thumb. Naming the cost of a choice alongside its benefit is what turns a fact into a design decision.

Answer: C

Overtightening strips the head thread and undertightening lets the plug run hot and blow out. The angle method genuinely is specified for some plugs, which makes the last option a real procedure for a particular type. A symptom that appears under one condition and not another is what narrows the diagnosis quickly. Most errors here come from carrying across a result from a neighbouring case where it does not hold. Naming the cost of a choice alongside its benefit is what turns a fact into a design decision.

Answer: D

Aluminium expands more than the steel plug, so a hot head grips harder and the thread can pull out. Penetrating fluid genuinely is used with care on seized plugs, which makes the last option a real if debated technique. The order in which the effects act is what decides the outcome, so it is worth establishing first. Naming what changes and what stays the same is the reliable route through questions of this shape. Reading the definition literally, rather than recalling a formula, is the reliable route through questions of this shape.