#2640: Flunking Physics Again
The Best of Car Talk
The Best of Car Talk May 19, 2026
#2640: Flunking Physics Again

#2640: Flunking Physics Again

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#2640: Flunking Physics Again
Term

air-fuel mixture

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

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

“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

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

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
Car

Nissan Silvia

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.

Honda Crx
Car

Honda Crx

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.

Volvo 240DL
Car

Volvo 240DL

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

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

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

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

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

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

“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

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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