ASE A1 Engine RepairFuel, Emissions, and Ignition Systems (General)Hard
A technician is diagnosing a vehicle with a consistent misfire on a single cylinder that occurs at all engine speeds. What is the LEAST likely cause of this specific type of misfire?
- AA faulty spark plug
- BA clogged fuel injector
- CA faulty ignition coil
- DAn intermittent electrical connection to a sensor
Show answer & explanationAnswer & explanation
Correct answer: D. An intermittent electrical connection to a sensor
A consistent misfire on a single cylinder at all engine speeds points to a hard failure of a component directly responsible for combustion in that cylinder (spark, fuel, or compression). An intermittent electrical connection to a *sensor* (like a crank sensor or cam sensor) would typically affect multiple cylinders or cause an intermittent misfire across the engine, or a no-start condition, rather than a consistent single-cylinder misfire.
Why the other options are wrong
- A. A faulty spark plug (e.g., cracked insulator, wrong gap) can cause a consistent misfire on one cylinder.
- B. A clogged fuel injector will consistently prevent proper fuel delivery to one cylinder, causing a misfire.
- C. A faulty ignition coil (e.g., internal short, open winding) will consistently prevent spark to one cylinder, causing a misfire.
Consistent Single-Cylinder Misfire
A persistent ignition or fuel delivery failure in one specific cylinder, manifesting as a misfire that does not vary with engine speed or load.
- Indicates a 'hard' component failure.
- Pinpoints ignition, fuel, or mechanical issues in that cylinder.
- Less likely to be caused by system-wide or intermittent sensor issues.
Memory trick: Consistent misfire, single spot, hard part failure, hit the plot!