To ohm a spark plug, you measure its electrical resistance using a multimeter. This process helps determine if the internal resistor within the spark plug is functioning correctly.
Step-by-Step Guide to Ohming a Spark Plug
Testing a spark plug's resistance is a straightforward process that requires a multimeter. Follow these steps:
- Prepare Your Multimeter:
- Get your multimeter ready for testing.
- Set the multimeter to the 20K ohms setting. This range is suitable for measuring the typical resistance found in resistor-type spark plugs.
- Position the Probes:
- Carefully position the two probes of your multimeter.
- Ensure that one probe touches the metal terminal end of the spark plug (the part that connects to the spark plug wire or coil pack).
- The other probe touches the top of the central electrode within the spark plug (the tip inside the porcelain insulator).
- Read the Measurement:
- Observe the reading on the multimeter display. This number represents the resistance of the spark plug in thousands of ohms (since the setting is 20K).
Reference Information Used:
- "To begin, grab your multimeter and set it to the 20K ohms setting."
- "Next, position the two probes of your multimeter ensuring that one touches the terminal end of the spark plug, and the other touches the top of the central electrode."
What the Reading Means
A typical resistor-type spark plug should show a resistance reading within a specific range, often between 3,000 and 10,000 ohms (3K to 10K ohms).
- Reading within the expected range: This usually indicates the internal resistor is functioning correctly.
- Very low reading (close to zero): This might indicate a non-resistor plug or a short circuit.
- Very high reading (over range or significantly above the expected range): This suggests excessive resistance, which can hinder spark energy.
- No reading (OL or infinity): This indicates an open circuit, meaning the resistor is broken and the plug is faulty.
Note: Always consult your vehicle's service manual or the spark plug manufacturer's specifications for the exact recommended resistance range for your specific spark plug.
Why Test Spark Plug Resistance?
Testing the resistance helps identify faulty spark plugs that may be causing misfires or poor engine performance due to an incorrect spark delivery. While visual inspection is important, measuring resistance provides insight into the plug's internal electrical health.
