Spark plug wires (also named “ignition cables”) carry high voltage present from your ignition coil(s) for the spark plugs. On older engines with distributors, the wires run in the distributor cap to the plugs, and come in diverse lengths to achieve the closest and furthest spark plugs. The wire set also involves an extra wire that connects the center terminal on the distributor cap to the ignition coil (unless the application is really a GM HEI distributor where the coil mounted inside the major of your cap).

On engines with distributorless ignition techniques (DIS), plug wires can also be employed to connect the coils to their respective spark plugs. On some engines, there’s one coil per spark plug, while on other folks with “waste spark” ignitions, two plugs share each coil.

On coil-on-plug (COP) ignition systems, there are no plug wires since the coils are mounted immediately on best in the spark plugs. But in coil-near-plug (CNP) techniques, you can find quick wires that connect the coils and plugs. On some applications, these wires are element of each and every coil assembly and can’t be replaced individually.


Spark plug wires come in three simple sorts:

Distributed Resistance wire. This sort has a fiber glass core impregnated with latex graphite. This type of wire offers the greatest number of radio frequency interference (RFI) suppression. RFI takes place when higher voltage passes throughout the plug wires. Making a controlled volume of resistance from the wire (3,000 to 12,000 ohms per foot) suppresses RFI and prevents delicate onboard electronics from choosing up false signals that may trigger driveability challenges.

One on the drawbacks of carbon core suppression wires is usually that internal resistance makes inner warmth. More than time, this ages the carbon core triggering resistance to boost. And as resistance goes up, so does the likelihood for ignition misfire.

Prior to 1980, 95% of all motor vehicles had been outfitted with carbon core suppression wires. But concerns in excess of emissions and prolonged expression reliability led quite a few with the Japanese OEMs to switch to “mag” type spark plug wires.

Inductance (mag) wire This variety features a spiral wound core of copper/nickel alloy wire. RFI is suppressed principally with the magnetic field formed through the loops of wire wrapped throughout the core as an alternative to the resistance of your wire itself. Mag wire has less total resistance (only about 500 ohms/foot) than suppression wire, so it lowers the current required to fire the plugs. The primary advantage is improved sturdiness above the long run.

Mag style spark plug wires have been made use of on Honda and Acura engines considering that 1971, most Nissan and Infinity applications given that 1980, and several Toyota and Lexus applications since 1984.

Fixed Resistor wire This sort of wire has a steel or copper metallic core by using a fixed resistor during the plug boot to regulate RFI. This wire is employed on many European imports.


Spark plug wires also use diverse varieties of insulation. Premium spark plug wire sets normally use silicone or EPDM (Ethylene Propylene Diene Monomer) insulation, with some having an outer covering of EVA (Ethylene Vinyl Acetate) for added temperature resistance and tensile strength.

Underneath the outer silicone, EPDM or EVA jacket is fiberglass braiding for strength and flexibility, and underneath that is certainly a layer of EPDM insulation that prevents arcing and voltage leaks. Mag core wire is normally surrounded by a latex silicone bonding layer that delivers supplemental stability and support to hold the spark plug wire in location.

SPARK PLUG WIRE Complications

spark plug wire insulation Irrespective of the sort of ignition system or the type of spark plug wires utilized, excellent plug wires are definitely crucial for dependable ignition overall performance and trouble-free operation. A terrible spark plug plug wire may possibly produce a lot resistance that the voltage never reaches the plug, or possibly a break while in the insulation might let the spark to arc to ground. In either case, a lousy plug wire will cause a spark plug to misfire.

Negative spark plug plug wires could cause tricky beginning (specifically for the duration of wet climate), poor fuel market, rough idle, hesitation when accelerating and enhanced hydrocarbon (HC) emissions. On 1995 and newer motor vehicles with OBD II Onboard Diagnostics, misfiring resulting from negative plug wires may perhaps also set a fault code and turn within the Examine Engine light.

Spark plug wires should generally be inspected if any of these symptoms are present, and when the spark plugs are improved. If wires demonstrate any apparent damage such as burned or cracked insulation, chaffing, loose plug boots or terminals, the wires must be replaced. Also, if visible arcing is present new wires are needed. Wires must also be replaced if their resistance measured finish to finish having an ohmmeter exceeds OEM specs.

As being a rule, if much more than one spark plug wire has excessive resistance, the whole set should be replaced.


substitute spark plug wires Spark plug wires are available in distinctive lengths, so match up the lengths with the unique wires so the wires fit correctly and don’t droop or rub.

Change ONE WIRE at a time to prevent mixing up the firing order (extremely important!). Start with all the longest plug wire(s) and visit the shortest or vice versa. For those who mix up the firing order, the engine may not start or it could pop and backfire. This could harm the engine so normally double-check the firing order if you’re unsure. Make reference to the firing order in a services manual or markings on the intake manifold, plug wires or distributor cap (if utilised). Note: Various vehicle producers amount they cylinders in different ways so make sure you know which plug is quantity one and the way the cylinder banking institutions are numbered.

The replacement wires really should be routed specifically the same as the originals, and supported by looms or clips so they don’t get hold of the exhaust manifold(s).

Additional items you could possibly require when replacing spark plug wires involve spark plugs, a spark plug boot puller (tends to make elimination and installation much easier), replacement looms or wire supports for original parts that might be missing, and dielectric grease for tight-fitting boots (can make elimination much easier upcoming time, and helps hold out water).