#2640: Flunking Physics Again
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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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.
The air-fuel mixture is the balance between air and gasoline (or other fuel) entering the engine. If the mixture is off—too rich or too lean—the engine can run poorly, misfire, or cause drivability issues like sudden RPM changes.
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.
RPM (revolutions per minute) is how fast the engine’s crankshaft is spinning. When the engine computer changes fueling or timing, RPM can rise or drop quickly, which is why RPM behavior is often used to diagnose problems.
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.
To “lean out” means the engine computer reduces fuel relative to air, making the mixture fuel-poor. A lean condition can trigger drivability issues and can also cause the O2 sensor to report values outside expected range.
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.
An O2 sensor (oxygen sensor) measures how much oxygen is in the exhaust. The engine computer uses that reading to adjust the air-fuel mixture so the car can burn fuel efficiently and keep emissions under control.
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.
In this context, “scan” refers to using a diagnostic tool to read trouble codes from the car’s onboard computer. Those codes can point to sensors like the O2 sensor or to conditions like “out of range.”
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.
The Nissan Silvia is a Japanese sports coupe known for its compact size and driver-focused feel. It’s often discussed in car conversations because it has a long-running history and a strong enthusiast following, especially among people who like tuning and track-style driving. In a podcast, it may come up as an example of a classic performance car name that’s recognizable even outside hardcore car circles.
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.
The Honda CRX is a compact, front-wheel-drive hatchback/coupe that became famous for its lightweight, sporty feel and strong reputation for being fun to drive. In this segment, the caller specifically mentions an “86 Honda CRX,” pointing to the early-1980s/late-1980s generation that enthusiasts often seek out for its simple, analog driving experience.
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.
The Volvo 240DL is a late-1970s/1980s Volvo 240-series sedan known for its durable, boxy design and straightforward mechanicals. The “DL” trim typically indicates a more comfort/feature-oriented version than the most basic models, while still using the same general 240 platform.
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.
In an engine context, “compression” refers to the pressure each cylinder builds up when the engine is cranking or running. Low compression usually points to worn rings, leaking valves, or other internal issues, while good compression shifts suspicion to fuel/ignition problems.
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.
CIS (Continuous Injection System) is a mechanical fuel-injection setup used on some German cars, where fuel is metered continuously and then delivered to the individual cylinders. Because it uses injectors and a metering system, a clogged injector can cause rough running or shaking even if engine compression is healthy.
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.
“Individual injectors” means each cylinder has its own fuel injector, so problems can be isolated to one cylinder’s fuel delivery. If one injector is clogged, that cylinder can run lean or misfire, contributing to vibration/shaking.
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.
A fuel injector “plugged up” with rust means debris has restricted the injector’s flow, preventing proper fuel delivery. In a CIS setup, that can cause one cylinder to run incorrectly, producing rough idle, misfires, and noticeable shaking even when compression checks out.
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.
A fuel injector is an electronically controlled nozzle that sprays pressurized fuel into the engine’s intake or combustion area. If an injector is clogged or fails, that cylinder may not get the right fuel, causing rough running or misfires. In the segment, the mechanic checks injector function by cranking the engine and watching the spray pattern.
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.
“Crank the engine over” means using the starter motor to spin the engine without necessarily starting it. This is often used for diagnostics because it lets you observe things like injector spray while the engine is turning. In the segment, they crank it to confirm which injector(s) are spraying.
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.
The fuel system is the network of components that stores, filters, pumps, and delivers fuel to the engine. If there’s heavy rust or contamination somewhere in that system, it can clog injectors repeatedly. That’s why the segment warns that even a newly replaced injector may get plugged up again.
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