Resistors Used in Spark Plugs & Spark Plug Wires

In early model vehicles before fuel injection and engine management computers, copper or stainless steel core spark plug wires were used. This type of wire was encased in rubber, and this type of construction produces high frequency magnetic pulses generated around the wires. The pulses cause heavy radio frequency interference that appears as the loud humming and static in the radio. RFI is also known as electromagnetic interference, or EMI.

Effects of RFI

RFI plays havoc with late model vehicles using computerized engine management systems and multiple computers for handling air conditioning, braking and so on. The magnetic interference interferes with sensor signals, as well as the computer-generated operating signals that result in anything from an engine miss or loss of power to a complete computer burnout, not to mention radio interference.

Solution

Resistor spark plugs and wires designed to suppress RFI are used in late model vehicles to protect the electronics and need service on a regular basis. Longevity is not an issue. The original equipment spark plug wires are carbon-core with a substrate of fiberglass an/or Kevlar, coated with high-resistance silicone or latex. These wires are effective in reducing RFI and handling the voltage produced by the stock ignition with a small fudge factor. A high performance ignition would burn them out rapidly. The carbon molecules burn away in the conductor over time, causing their failure. A high performance ignition system producing higher voltage burns them out more rapidly.

Spark Plugs

All spark plugs used in late model vehicles are of the resistor type. There is a resistance material or gas located in the area between the ceramics and the threads on the center conductor. The resistor is of a low value and has no adverse effect on the spark output.

High-Performance Spark Plug Wires

Many claims are made by the manufactures about horsepower increases in the competitive market, but this has never been proven. The case in point is increased longevity. Spiral core wires, which have a larger diameter, have longer service life even with high-performance ignitions. They use closely wound wire over a highly resistant carbon-impregnated silicone or latex compound coating. Even with this construction, it is at best difficult to verify a horsepower advantage.