Today: Eli and the impudent coil wire.

Dear Car Talk

Dear Car Talk | Sep 01, 2011

Dear Tom and Ray:

Hi! My name is Eli, and I have a quick question for you. I live in North Carolina, I'm a teenager and I am a mechanic's assistant. I've been working in the shop for about a month now (so I'm sure you're wondering why someone with SO much experience is asking you guys a question!).

When you pull the coil wire, what does it do to render the car impudent? I think that's the right word. If you have time to reply, that would be great!

-- Eli

TOM: I think you mean impotent, Eli. The word you used -- "impudent" -- means "rude or disrespectful." "Impotent," on the other hand, means "without power."

RAY: Of course, "impotent" also can refer to one's own coil wire, but we won't go there.

TOM: Right. Anyway, Eli, to make a cylinder fire, you need three things: gasoline, air and electricity. When you unplug the coil wire, you're essentially shutting off the electricity.

RAY: The coil takes electricity from the battery, jacks it up to a nice, high voltage and then sends it to the distributor. The distributor then does what? Distributes it! It sends the voltage through the appropriate spark-plug wire to a given spark plug at just the right time.

TOM: Actually, this is how a coil USED TO work. But most cars these days don't have coils and distributors anymore. They've been disappearing for the past decade or so.

RAY: Right. Now that spark plugs need much higher voltages for more complete combustion (and therefore fewer emissions), the single coil has become an increasingly inefficient way to generate the voltage. By the time you send the charge through all those wires, too much electricity is lost, and the chance of an engine misfire increases.

TOM: So now, most cars have individual coils right at each spark plug. It's called "coil-on-plug technology." And instead of the 15,000 or 20,000 volts generated by the single coil, the individual coil packs can send 90,000 or 100,000 volts right into the spark plug with very little leakage.

RAY: So modern cars can no longer be disabled by unplugging the coil wire, Eli, because they don't have coil wires. And that's a good thing. Because when you disable a car and it can't start, it gets angry, and may even become impudent.

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