ASE A1 Engine RepairFuel, Emissions, and Ignition Systems (General)Medium
A vehicle experiences a misfire on cylinder #3. The technician swaps the ignition coil from cylinder #3 with cylinder #1, and the misfire moves to cylinder #1. What is the most likely cause of the original misfire?
- ALow compression in cylinder #3
- BA faulty ignition coil that was originally on cylinder #3
- CA faulty spark plug in cylinder #3
- DA clogged fuel injector in cylinder #3
Show answer & explanationAnswer & explanation
Correct answer: B. A faulty ignition coil that was originally on cylinder #3
By swapping the ignition coil and observing the misfire move with the coil, the technician has successfully isolated the faulty component. This indicates the ignition coil itself was the cause of the misfire on cylinder #3.
Why the other options are wrong
- A. Low compression is a mechanical issue with the engine cylinder and would not move with an ignition coil swap.
- C. If the spark plug was faulty, the misfire would have stayed on cylinder #3 after the coil swap.
- D. If the fuel injector was clogged, the misfire would have stayed on cylinder #3 after the coil swap.
Misfire Isolation by Swapping
A diagnostic technique where a suspected faulty component (e.g., spark plug, ignition coil, injector) from a misfiring cylinder is swapped with a known good component from another cylinder to see if the misfire follows the component.
- Effective for single-cylinder misfires.
- Helps pinpoint specific faulty components.
- Requires careful tracking of swapped parts.
Memory trick: Misfire moves, component's bad, don't be sad, just swap it, Dad!