The usual causes for this problem are as follows:
(1) The wires have not been correctly fitted — see FAQ’s: “What are the most common problems with with ignition wires?” and “Why are sparks jumping from the boots and cable jacket?” Also make sure the wires have been fitted to the engine in the correct cylinder firing sequence.
(2) Often, DIY’s just replace ignition wires in an endeavor to rectify an engine miss, only to discover the problem is not solved because other ignition components are contributing to the problem. When Magnecor Race Wires are installed on an engine with deteriorated ignition components, an engine miss can seem worse, because the full coil output current conducted by Magnecor wires, via the distributor, to the spark plugs tends to find every weakness in a deteriorated ignition system that wasn’t so apparent when coil output was absorbed (and wasted) in the original carbon conductor or resistor-connector type ignition wires. Each time you replace ignition wires, it’s important you at least closely inspect the distributor cap and rotor, as well as the ignition coil tower (or coil pack towers on a DIS) for condensation accumulation, cracks and burning. If the distributor cap and rotor have run in excess of 50,000 miles (80,000 Km), replacement should be considered. Spark plugs also should be inspected and re-gapped if necessary. Unless spark plugs are the double platinum type, it’s wise to replace any that have run in excess of 30,000 miles (50,000 Km). All turbocharged or supercharged engines are hard on spark plugs, and even a relatively new spark plug can develop cracks in the porcelain insulator, allowing combustion gas to escape inside a wire’s boot or connector, and arcing can occur down a spark plug’s porcelain and ground out from under the wire’s boot or connector seal. Always look for dark colored gas leaks and cracks on the outside of the spark plugs’ porcelain.
(3) When an engine runs rougher after replacing a multitude of ignition system components including ignition wires (usually installed last of all), DIY’s often conclude the wires must be the cause. If Magnecor ignition wires are installed correctly, it’s almost impossible for the wires (by themselves) to cause the engine to run roughly. Rough engine running problems do occur when ignition points, electronic modules, pickup coils, rotors, and distributor caps are not properly installed or damaged, or wiring to these components is disturbed or damaged. Also, vacuum tubing and wiring associated with timing devices connected to the distributor and other engine management components can also be disturbed or damaged and cause the engine to run roughly. If this problem does occur, every component should be checked, keeping in mind that improper installation can terminally damage electronic components.