Automotive Service Excellence (ASE) A8 Engine PerformanceIgnition System Diagnosis and RepairMedium
A client complains of a rough idle and occasional stalling on their vehicle. A technician connects a scan tool and finds no diagnostic trouble codes (DTCs). Further investigation reveals that the engine intermittently runs lean. When checking the ignition system, the technician measures the primary ignition coil resistance and finds it to be significantly higher than specifications. What effect would this high primary resistance MOST likely have on the ignition system?
- AReduced current flow through the primary winding, resulting in a weaker secondary spark.
- BNo significant effect, as primary resistance is self-regulating.
- CFaster collapse of the magnetic field, advancing ignition timing.
- DIncreased secondary voltage output, leading to premature spark plug wear.
Show answer & explanationAnswer & explanation
Correct answer: A. Reduced current flow through the primary winding, resulting in a weaker secondary spark.
Higher primary coil resistance restricts current flow through the primary winding. This reduced current flow weakens the magnetic field build-up in the coil, leading to a weaker collapse of the field and thus a lower, weaker secondary voltage and spark.
Why the other options are wrong
- B. Primary resistance is critical; deviations from specifications will significantly affect coil operation and spark output.
- C. High resistance slows down current build-up and reduces magnetic field strength, not necessarily speeding up its collapse or advancing timing.
- D. Increased primary resistance leads to reduced current, which would decrease, not increase, secondary voltage.
Primary Coil Resistance
The electrical resistance of the primary winding within an ignition coil, which controls the current flow that builds the magnetic field.
- Too high resistance reduces primary current.
- Reduced primary current weakens magnetic field.
- Weaker magnetic field results in weaker secondary spark.
Memory trick: Primary current builds the spark, resistance restricts it.