You cannot and should not zip tie spark plug wires together as they can crossfire and cause the engine to run rough.
Spark plug wires do need to be separated because when spark plug wires are too close together it can cause the electricity to cross between the wires and cause the engine to crossfire and misfire.
Bundling of spark plug wires and wrapping them with tape, pulling them through metal tubes or dressing them tightly against the engine, may make them look neat but can cause serious voltage losses and/or crossfiring.
Changing the routing from the original OEM routing can lead to early spark plug wire failure.
To best see any sparks, run the engine in a dark place and watch the spark plug wires and the ignition coil.
Spark plug wires which are too close together can INDUCE spark in each other.
If your vehicle has spark plug wires, most owner's manuals recommend that the wires be replaced at the same time as the spark plugs, so you'll probably want to have both new plugs (the correct ones for your vehicle) and new wires on hand before you start the job.
Screwing up the plug wire order would cause cylinder misfires, and the unburned fuel usually flow out to exhaust and potentially damage the O2 sensors and Cat – but should not happen with only few seconds of cranking the engine.
Like all maintenance services, the ideal interval for changing your spark plugs and wires depends on the manufacturer's recommendations.
Most cars need them done at 30,000 to 60,000 miles, while others are good until 100,000 miles.
The most important thing to remember is to change the wires when you do the spark plugs.
High-quality wires will allow the spark plugs to start faster and keep your engine running more effectively.
Save money. Routinely swapping out your spark plug wires can save you cash.
Driving on faulty wires can end up damaging your vehicle if you don't switch out the wires quickly enough.