Elusive Vacuum Leak

The Puzzler

RAY: Hi, we're back. You're listening to Car Talk with us, Click and Clack, the Tappet Brothers, and we're here to discuss cars, car repair and the new Puzzler. Now, I thought, it being this early in the Puzzler season, that I ought to use an automotive Puzzler of one kind or another.

TOM: Ah!

RAY: Because I haven't had one yet.

TOM: I hadn't even noticed that.

RAY: I didn't think you would have. And here it is, if I can remember it.

TOM: Yes.

RAY: A few months or weeks ago, one of my guys was under the hood of an old...I don't remember what it was. It was an old Chevy pickup truck...trying to find a vacuum leak. Now, what a vacuum leak is, is it's a leak which allows air to get into the engine when it shouldn't be getting in through that spot.

TOM: Specifically, into the combustion chamber.

RAY: Into the combustion chamber. All the air that enters an engine should come either through the carburetor, if the car has one, or through the throttle body, and any air that comes in through any other source is called a vacuum leak, and it affects the way the thing runs. If the leak is sufficiently large, the thing won't run at all, or it certainly won't run at idle, and it'll stall out every time you take your foot off the gas, and that's exactly the problem that this thing had.

TOM: Mm-hmm.

RAY: So, there he is. And the way you find vacuum leaks is, either you get lucky and you hear the hissing, and you say, "Ah, there it is!" And you put your finger on a hose that's broken or a pipe that's gotten disconnected, or we use a little wand that shoots propane, and you go around with this thing attached to, the other end of which is attached to a propane tank, and you squirt this propane all over the place. And when the vacuum leak and the propane meet, you'll suck the propane in and the engine will begin to run smoothly, and, in fact, it will even idle, because now you're making the fuel-air mixture correct. Are you with me so far?

TOM: Right. And as soon as you take the propane wand away, all of a sudden, you've got far more air compared to the fuel than you're supposed to have, and it runs lousy again.

RAY: Exactly. So there he is with the wand, and he's having lousy luck.

TOM: He's underneath the vehicle?

RAY: No. He's under the hood.

TOM: Under the hood. OK.

RAY: Under the hood, and the engine is running, but the leak is so big...the leak is so pervasive and yet so evasive, that he can't seem to find it.

TOM: Wow.

RAY: Plus the fact that, on a pickup truck, you feel a dangling in the ears. Stuff is falling out of your pockets. It's a pain. So in desperation he throws the stuff down, and he shuts off the engine. And a few minutes later, I walk by, and I see him doing something very interesting. He's pulling off the spark-plug wires and he's putting them back on, but on the wrong plugs.

TOM: Mmm.

RAY: I say...

TOM: "What do I care? None of my business."

RAY: None of my business! Why should I care?

TOM: Maybe it'll work better.

RAY: And I walk away.

TOM: Yeah.

RAY: Two minutes later, I hear him on the phone ordering the part that he needs to correct the vacuum leak. How did he do it?

Think you know? Drop Ray a note!

[ Car Talk Puzzler ]

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