A technician is diagnosing an intermittent misfire on a vehicle with a Waste Spark ignition system. The misfire predominantly occurs on cylinder #1 and cylinder #4. During testing, the technician measures the spark plug resistance for both cylinders and finds that cylinder #1 has significantly higher resistance than cylinder #4. What is the MOST likely implication of this finding in a waste spark system?
- AThe misfire is likely due to a shared ground circuit problem for both cylinders.
- BA defective crankshaft position sensor is providing an inconsistent signal.
- CThe high resistance in cylinder #1's spark plug is directly causing the misfire in that cylinder.
- DA faulty ignition coil primary winding for cylinders #1 and #4.
Show answer & explanationAnswer & explanation
Correct answer: C. The high resistance in cylinder #1's spark plug is directly causing the misfire in that cylinder.
In a waste spark system, cylinders #1 and #4 are paired and share a single ignition coil. If cylinder #1's spark plug has significantly higher resistance, the coil will preferentially send its spark to the lower resistance path (cylinder #4's plug), leaving cylinder #1 with an insufficient spark and causing a misfire, even if cylinder #4 is firing correctly.
Why the other options are wrong
- A. A shared ground issue would affect both cylinders equally, not cause one to misfire more severely due to spark plug resistance differences.
- B. A defective CKP sensor would affect all cylinders or cause more widespread issues, not a misfire isolated to one cylinder of a waste spark pair due to plug resistance.
- D. If the primary winding were faulty, both cylinders #1 and #4 would likely misfire or have weak spark equally, not just one due to spark plug resistance.
Waste Spark Resistance Imbalance
In a waste spark system, if one spark plug in a paired cylinder has significantly higher resistance than the other, the ignition coil's spark will preferentially jump to the lower resistance plug, causing a misfire on the high-resistance plug.
- Paired cylinders share one coil.
- Spark takes path of least resistance.
- Resistance difference causes misfire on higher resistance plug.
Memory trick: Waste spark's path of least resistance determines the spark.