What if my spark plug gap is too big?
If the spark plug gap is too large, you’ll likely experience hard starting, misfires, reduced power, and lower fuel efficiency. The remedy is to re-gap the plug to the engine’s specification or replace the plug altogether to restore reliable ignition.
Why the gap size matters
The gap between the center and ground electrodes sets how much voltage the ignition system must deliver to create a spark. A larger gap demands more voltage and a stronger spark energy. If the ignition system can’t consistently jump that larger gap, the spark may fail to occur, especially under high engine load or during rapid RPM changes. This can accelerate electrode wear, stress ignition coils or coil packs, and increase emissions if combustion is incomplete.
How a large gap can affect ignition energy
A wider gap requires higher voltage and more energy to form a stable spark. If the coil, coil-on-plug module, or wiring can’t supply that energy consistently, you may see misfires, rough running, and reduced power. Over time, repeated misfires can damage the catalytic converter and raise exhaust emissions.
Symptoms of a gap that’s too large
Be on the lookout for several telltale signs that a plug gap may be oversized. The following indicators are commonly reported:
- Hard starting or extended cranking to start the engine
- Engine misfires, especially under acceleration or load
- Rough idle or noticeable hesitation at low RPM
- Loss of power and sluggish throttle response
- Increased fuel consumption and higher emissions
- Check Engine Light with misfire-related codes (for example P0300 series)
These symptoms point to disrupted ignition energy due to an oversized gap, but a measurement is needed to confirm the cause.
What to do if you suspect a gap is too large
Follow these steps to diagnose and address a spark plug gap that may be out of spec:
- Obtain the correct gap specification for your engine from the owner’s manual, service manual, or the spark plug packaging. Common passenger-car gaps range roughly from 0.7 to 1.5 mm (0.028–0.060 inches).
- With the engine cool, remove the spark plug using an appropriate spark plug socket.
- Inspect the plug: if the center or ground electrode is worn, or if the plug is fouled or damaged, replace it rather than attempting to re-gap.
- Measure the current gap with a calibrated feeler gauge and compare it to the manufacturer’s spec.
- If re-gapping is permissible for your plug type, carefully adjust the gap using a proper gap tool. Bend the ground electrode only slightly, and avoid applying force to the center electrode.
- Re-check the gap to spec, then reinstall the plug with the correct torque for your engine. Do not over-tighten.
- Run the engine and observe for improvement. If misfires persist, diagnose ignition components or fuel systems, or seek professional help.
Note: Many modern iridium or platinum plugs are designed with a fixed gap and should not be re-gapped beyond manufacturer allowances. If you’re unsure, replace the plug with the correct fixed-gap type rather than attempting a risky adjustment.
When to re-gap vs. replace
In general, lightweight re-gapping is acceptable for some copper-core or conventional plugs within a small tolerance. However, iridium or platinum plugs often have a fixed gap and are more susceptible to electrode damage from bending. If the gap needs to be adjusted beyond a small amount or the electrode shows wear, replacing the plug with the correct specification is usually the safer option. If you notice repeated misfires after re-gapping, consider replacing all plugs to ensure uniform ignition performance.
Preventing gaps from drifting
Preventive maintenance helps keep gaps within specification and preserves ignition performance. Consider these practices:
- Use OEM or recommended plugs for your vehicle and avoid mismatched types.
- During plug replacement, measure and set the gap accurately before installation.
- Avoid reusing worn plugs; install fresh plugs when in doubt.
- Install plugs with proper torque to prevent electrode damage and seating issues.
- Replace worn ignition components (wires, coil packs) that can affect spark energy.
Regular inspection and adherence to the manufacturer’s gap specification help prevent ignition problems related to an oversized gap.
Summary
Keeping spark plug gaps within the manufacturer’s specification is essential for reliable ignition and efficient engine operation. If you discover a gap that’s too large, re-gap to spec or replace the plug as needed. Use the correct tools, follow torque guidelines, and if misfires persist, have the ignition and fuel systems checked by a professional. Consistent maintenance will protect performance, fuel economy, and emissions.
