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#2640: Flunking Physics Again

#2640: Flunking Physics Again

The Best of Car Talk May 19, 2026 35 min
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About this episode

A call-in begins with a 1994 Chevy pickup owner describing their 350 (5.7L) V8 and mileage, then the discussion shifts to a drivability diagnosis: the hosts suspect “a bad oxygen sensor” that could mislead the computer into thinking the mixture is “way too rich.” They also walk through how dealers can test the O2 sensor and what codes might appear. Later, a physics-themed segment turns into a rope-and-angle calculation for getting a car moving, before the show returns to real-world storage and repair talk.

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Technical Too Afraid to Ask
Term

air-fuel mixture

"It leans out the mixture tremendously and causes the RPM to drop suddenly."

Your engine needs the right mix of air and fuel to run smoothly. If the mix is wrong, the car can feel rough or act weird, including sudden changes in RPM.

Term

RPM

"It leans out the mixture tremendously and causes the RPM to drop suddenly."

RPM means how fast the engine is spinning. If something changes in how the engine is running, the RPM can jump or drop, and mechanics use that as a clue.

Term

lean out

"It leans out the mixture tremendously and causes the RPM to drop suddenly."

“Lean out” means the engine is getting less fuel than it should compared to the air. That can make the car run poorly and can show up in the O2 sensor readings.

Term

O2 sensor

"So you need to take it to your Chevrolet dealer, or whomever you take it to, and ask them to test the O2 sensor. They can scan it if they want."

The O2 sensor checks the oxygen level in your car’s exhaust. Your engine uses that info to adjust how much fuel it mixes in, so the engine runs right and the emissions stay in check.

Term

scan

"They can scan it if they want. They can put the machine on it."

Here, “scan” means plugging in a computer to read error codes from the car. Those codes help identify what sensor or system is acting up.

Nissan Silvia
Charlie from United Kingdom (CC BY 2.0)
Car

Nissan Silvia

"...but. And she was mostly going to have coffee with Silvia Poggioli. But the government has offered to put y..."

The Nissan Silvia is a sports car made by Nissan. It’s a smaller, two-door car meant to feel fun to drive, not like a big family car. People talk about it a lot because it’s been around for many years and has a reputation with car enthusiasts.

Car

Honda Crx

"But the government has offered to put your car into storage, your 86. Honda CRX. You remember that?"

The Honda CRX is a small Honda that people like because it’s light and drives in a sporty way. Here, they’re talking about a 1986 Honda CRX that the government is storing while the owner is away.

Car

Volvo 240DL

"And you have a car? [1681.5s] I have a car. [1682.8s] It's a Volvo 240DL. [1685.6s] It's a 1980."

The Volvo 240DL is an older Volvo sedan from the 240 series. People like it because it’s simple and tough, and the “DL” usually means it’s a nicer-equipped version of the same basic car.

Term

compression

"What about the shaking, though? ... It could be that you have bad compression. And I would imagine that whoever looked at this thing has checked the compression."

Here “compression” means how well each engine cylinder is sealing and building pressure. If compression is low, the engine can misfire or run rough; if compression is good, the problem is more likely elsewhere.

Term

CIS, Continuous Injection System

"But if it didn't, this thing has a fuel injection called CIS, Continuous Injection System, and it has individual injectors for each cylinder."

CIS is a type of fuel injection system that delivers gasoline to the engine in a controlled way. If one injector gets clogged, that cylinder may not get the right fuel, and the engine can shake or run poorly.

Term

individual injectors

"CIS, Continuous Injection System, and it has individual injectors for each cylinder. So let's assume he did a compression test and the compression is good."

With individual injectors, each cylinder gets its own fuel sprayer. If one sprayer is clogged, that cylinder may not get enough fuel and the engine can shake.

Term

injectors is plugged up with rust

"The thing I'd most likely suspect is that one of the injectors is plugged up with rust."

If rust clogs a fuel injector, that cylinder doesn’t get the right amount of fuel. The result can be rough running and shaking, even if the engine’s compression is fine.

Term

fuel injector

"He said, maybe there's a fuel injector problem. What he can do is he can pull out the injectors. And he can actually crank the engine over and watch the injectors spray, all three of them."

A fuel injector is a small part that sprays fuel into the engine. If one injector is clogged or not working, that cylinder won’t get fuel and the engine can run badly. They’re checking it by starting the engine briefly and looking to see if each injector sprays.

Term

crank the engine over

"And he can actually crank the engine over and watch the injectors spray, all three of them. Okay."

“Crank the engine over” means turning the engine over with the starter. It spins the engine so you can test parts without fully starting it. Here, they do it to see whether the injectors spray.

Term

fuel system

"but there may be so much rust in the whole fuel system that they're all going to get plugged up eventually, even the new one."

The fuel system is everything that gets fuel from the tank to the engine. If it’s rusty or dirty, it can clog the injectors again and again. That’s why replacing one injector might not be enough if the rest of the system is contaminated.

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