And so, it seems that the time has come to change the spark plug cables; in fact, these wear out over time, usually both at the point of connection with the coil and at the point of connection with the spark plug itself. You will need to locate the wires, determine their length, and gently detach them from the spark plugs.
Steps
Part 1 of 3: Preparing for the Replacement
Step 1. Lift the hood of the vehicle
The release lever is usually located on the driver's dashboard, lower left. Some cars are equipped with a hydraulic system that allows the bonnet to remain raised automatically. Either way, you need to make sure it doesn't fall on you while you're working on the engine.
Step 2. Locate the spark plug leads
They are generally located near the valve covers on the cylinder head. One end of each harness is attached to a spark plug, while the other connects to the ignition coil or distribution.
Step 3. Understand the reasons why the cables wear out
These elements tend to increase more and more their resistance to the flow of electricity due to the high voltage that constantly runs through them. Eventually, the resistance becomes too high for the current to flow. The higher the resistance, the less energy reaches the spark plugs - as a result, incomplete combustion of the fuel inside the cylinders is achieved. If you notice any damage to the protective sheath that covers the spark plug wires, you need to replace them.
Step 4. Evaluate if replacement is necessary
The age of the cables alone does not necessarily indicate that you need new cabling. Check for damage and listen for engine noise for malfunctions. If you notice sparks coming out of the cables and going towards the engine, it means that you need to have it replaced.
- Be aware of some obvious symptoms of engine problems - it may "spin" erratically, "skip" at idle, or make a deep "coughing" noise. These can be the consequence of malfunctioning spark plugs or other more serious anomalies; therefore, the first thing to do is to check if the cables are damaged and if they need to be changed.
- If you notice sparks falling to the ground in the evening when the hood is raised and the engine is running, you need to change the spark plug leads. Depending on their conductivity, there may be sparks escaping from the entire front of the vehicle or from just one point.
- Look for obvious defects in the cables. They may be frayed, cracked and even show burns. The presence of any or all of these signs indicates that you need to get new ones.
Step 5. Evaluate how many cables you need
Once you know the type and quantity, you can purchase them from an auto parts store. The salesman will help you in your choice and will confirm that you are buying the right pieces.
Step 6. Verify that the parts are the correct length
You have to buy the whole kit, even if you only have to change one. So, if the car engine has six cylinders, you need to purchase all six cables which have different lengths. It is important to check this by comparing the cable you are about to fit with the old ones that are still on the motor. Try to respect the original dimensions as much as possible.
- The various manufacturers produce cables of different lengths and often the spare parts are longer than the original ones. This way, they can sell more kits that fit different cars; you may therefore notice some small differences. Check the length of the wiring before starting and you will have no problems.
- Quality matters. Avoid kits that allow you to vary the length of the harnesses, unless they are of high quality and you are not very good at assembling the connectors yourself.
- Most often manufacturers do not allow repairs on their cables. Start cutting them to a certain length only and exclusively if you know for sure that the new end can be connected securely; otherwise you will regret it.
- Some auto parts stores sell fully assembled individual spark plug leads.
Part 2 of 3: Disconnect the Cables
Step 1. Make sure the car is turned off
Never try to replace the spark plug wires with the engine running. Likewise, do not perform maintenance when the engine compartment is too hot to touch.
Step 2. Take an inventory
Once you have identified the cables, take note of the length and position of each of them, because you will have to connect each spare respecting the exact housing of the damaged ones - the operation will be much easier if you write down these details. If you connect the wiring in the wrong order, the engine may not start or malfunction. Try to label each wire with duct tape and a number (corresponding to the spark plug it is connected to), so you won't get confused.
Step 3. Be methodical
Replace one cable at a time, following a specific order or direction. This method helps you remember their exact location and reduces the risk of altering the timing of the firing order. Take your time. Start with one cable and complete its installation before moving on to the next.
- Both ends of the cables are connected to elements. You will need to detach them before fitting the replacement.
- The spark plug should ignite when the corresponding piston is almost at the highest point of the cylinder. For this reason, it is vitally important not to alter this sequence. Start at one end of the engine and work in a specific direction.
Step 4. Disconnect the cables
Use the tool to disconnect the ends and remove them. Be very careful when dealing with the end attached to the candle. Modern engines have a rubber connector that adheres tightly to the spark plug to keep it clean and dry. Detach the cable by pulling it by the connector. If you apply traction to the cable itself, you may break it leaving fragments attached to the spark plug.
- Some cables adhere very strongly to the spark plugs. Grasp the rubber connector firmly. If you can't pull it off immediately, try twisting it slightly as you pull.
- Inspect the connector for traces of carbon. These are black lines running down from the top of the spark plug, the one hidden under the connector. If you notice them, you must also take the spark plug apart to check it.
Part 3 of 3: Install the New Cables
Step 1. Work backwards
Connect the new cables respecting the order in which you removed the old ones. Before inserting the connector to the spark plug, add a small amount of dielectric grease inside. When you hear a slight "click", you are certain that the connector is firmly attached to the spark plug. The cables connect the spark plug to the distribution or ignition coil and must be replaced respecting the original arrangement. By combining the coil with the wrong spark plug, the engine will not run and could be damaged. Make sure that the wiring is away from the elements of the exhaust system, as they could get damaged and be careful not to cross them.
- The spark plug cables are generally inserted in cable ties or in special frames. If a harness leans against the motor or crosses with another, it can create a short circuit, lose energy, or break due to heat. For this reason, you need to make sure that the cables are routed correctly within the cable ties or frames, away from metal elements.
- If you are replacing cables with a high performance coil and kit, remember that they may not fit the original frame and grommets. In this case, you need to buy a new frame with a larger diameter or enlarge the holes of the cable glands.
Step 2. Close and lock the hood
Try lifting it up after closing to make sure it's not partially loose. You shouldn't be able to open it without first operating the lever in the cockpit.
Step 3. Listen to the engine
After installing the new cables in their place, start the engine. It should work and idle without difficulty. You should also note that it has more power and is more efficient, especially if the old cables were heavily worn. If the engine does not start, runs erratically, or backfires after replacement, check for incorrectly routed cables connected to the wrong cylinder, grounded along their path, poorly assembled to the connector or that the connector itself is well stuck to the coil or spark plug.
- Never touch the cable when the motor is running, otherwise you will receive a very painful shock. The ignition system generates tens of thousands of volts, and a poorly installed wire could electrocute you. Since there is less grounding at the end of the spark plug, your body provides an easier path for electrical current.
- If you notice a backfire when the engine idles or other performance issues, you have probably plugged a cable in the wrong place. Consider taking the car to a mechanic to diagnose and fix the problem.
Step 4. Take a road test
While driving, try to put pressure on the engine by driving uphill or slowing down in a high gear; subsequently, it accelerates by switching to a lower ratio to stress the injection system; this, in fact, is more likely to show malfunctions when put under stress.
Step 5. Finished
Advice
- If possible, disconnect and replace only one spark plug and cable at a time to avoid confusing the arrangement.
- Some vehicles do not have spark plug leads, which are equipped with a coil instead.
- Always take note of the position of each candle. It is essential that each be returned to the housing from which it was removed.
- If you spray water on a spark plug wire with the engine running, you may notice a spark escaping from one side of the wire, the one grounded to the engine block. This phenomenon indicates that the spark plug wiring is faulty.
