Do you have enough voltage reaching your spark plugs?
The voltage required to light your plugs is constantly changing and can range from 5,000 volts to 40,000 volts and higher, depending on your engine setup. That’s why many high performance engines use a high-output ignition coil to deliver the voltage needed.
The job of the ignition coil is to step up the ignition system’s primary voltage (typically 12 volts) to the voltage required to create the spark and then hold it for a millisecond. When an ignition coil falls short on voltage, your engine may experience misfire, starting problems, and other types of poor performance. Insufficient voltage is often caused by ignition coil failure due to excessive heat, vibration, or high resistance in your spark plugs or ignition wires. In some cases, your ignition coil simply may not be rated to deliver the voltage required.
The point is you’ll want to pay attention to your spark plugs’ voltage requirements in high performance applications. In conjunction with Autolite, we’ve put together seven factors that can affect the amount of voltage needed from your ignition system.
Spark Plug Gap
Voltage needs to rise in proportion to the size of the spark plug gap. It’s important to note that the spark plug gap widens as the electrodes wears so the age of the spark plug may necessitate a higher voltage, depending on the electrode condition.
If you look closely at the ground strap electrode of a spark plug, you may notice precisely honed edges and even a raised platinum tip. These are scientifically designed to enhance ignition. Over time, these edges will wear and become more rounded, requiring more voltage in order to generate a proper flame kernel.
Voltage requirements rise in relation to cylinder pressures, which are highest at low speed and high load situations, such as accelerating from a standstill. Under these circumstances, and under high-rpm operation, higher voltage is required to avoid misfires.
The leaner the air/fuel ratio — the less gasoline per volume of air — the higher the voltage requirements. As automakers try to make engines more fuel efficient with fewer exhaust emissions, lean air/fuel ratios are common. But if the air/fuel ratio becomes too lean, a misfire could occur.
The lower the overall engine temperature, the higher the required voltage. Misfires can occur more readily at low operating temperatures.
As the electrode temperature rises, the required voltage drops. Since electrode temperature rises at higher engine speeds, misfires can occur more readily at low engine speeds.
As the ambient humidity rises, electrode temperature decreases, requiring higher voltage to generate a proper flame kernel.
‘s up, on spark plug voltage.
I have a 1999 Polaris sportsman 500 liquid cooled and I have a spark plug in the atv then I go out riding for a couple hours come back and won’t start but then I put a new plug in runs great but then it repeats and does it again what could cause this
Hi David, many thanks for the very interesting information, it has helped my understanding of fuel combustion.
Could you please help with a theory I have? …….I believe that in some cases, resistive spark plugs can cause a heavier voltage draw due to the resistance to voltage flow where voltage is ‘peaking’ to find earth on the earth tab of the spark plug. Am I thinking totally of the mark here David?
I have a two-stroke outboard motor that is eating resistive plugs.
Kind regards ….Tom.
I have a 1962 Thunderbird withers a 390. When I rebuilt the engine I switched the points and condenser out for an electronic ignition and a flame thrower coil. Since then it has always run very hot. My question is, does the higher voltage affect engine temperature and does it change the ignition timing from the original factory recommendation??