2 days ago I felt that something isn't right with my Ford.
A mechanic told me that he wants to replace all four spark plugs and wires but could I just change the spark plugs?
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Here's the reason.
If your spark plugs have been in the engine too long the component at the end of the plug get's oxidized over time from having such high voltage run across it to jump a gap and create a spark. As these electrodes are consumed by this process the gap becomes wider and wider and it makes it more difficult for the spark to jump that gap. As the gap increases (it's called an air gap) the resistance increases. Resistance in electrical speak is called ohms. As the ohms increase more voltage is required to jump the gap. As the resistance increases there additional side effects, one of them is heat. It's a byproduct of the process. As the heat increases in the spark plug wires and the resistance increases during the spark/ignition process the wire inside of the spark plug wire slowly get's broken down, this also increases the resistance that your spark coils need to overcome. So they heat up and start breaking down over time with heat.
I was taught by my father, an electrical engineer from CAL Berkeley, to replace the spark plug wires every third spark plug change. This was in the late '70's soooooo...take it with a grain of salt. As well, he also advocated, if your having an ignition problem, don't screw around, change the plugs, the wires and distributor cap.....the stuff is a consumable and is the price you pay kid....well, he always seemed to fix the problem and didn't burn a bunch of money and time trying to figure it out. Additionally, he didn't damage the rest of his system trying to save a buck.
I understand that when money is tight, money is tight....so this is a subjective question and I'm giving you my honest OPINION. There are no facts, there isn't enough information about what you are experiencing.
The long and short of it.......
You don't need to change your spark plug wires when you change your spark plugs but if you are taking it to a mechanic and he is charging you.....you may want to avoid the 2nd visit. It's up to you and your situation. I, thankfully, am not experiencing the agony of financial distress so I'd change them but I'm not you. You know the risks now and whatever you choose to do won't be right or wrong it will just be.
Hope the situation works out as best it can.
Good luck and cheers :)