If these GM cars are fuel injected, why do I see a carburetor on their engines?

Dear Car Talk

Dear Car Talk | May 01, 1995

Dear Tom and Ray:

I'm confused about fuel injection on GM cars and trucks. I've noticed that the V6 and Cadillac V8 engines are fuel injected, but the V8 trucks are not. They call them "electronically fuel injected," but there's still a carburetor sitting on top of the engine. What's the explanation for this?

RAY: Good question, David. Those GM truck V8s DO have fuel injection. In fact, ever since Yugo rowed back to Europe a few years ago, nobody sells a new car with a carburetor any more.

TOM: Compared to fuel injection, carburetors were rather crude devices that basically poured gasoline into the cylinders. Technologically, they were just one step removed from coffee cans full of gas with holes punched in the bottom of them.

RAY: Fuel injection is a system which precisely meters the amount of fuel going into the cylinders. And because it does that, a lot less gasoline is wasted, and fuel economy and emissions are improved dramatically.

TOM: And let there be no doubt about it. ANY fuel injection system is better than even the best carburetor. But not all fuel injection systems were created equal, and there are three basic types.

RAY: The GM trucks you refer to have what is called "throttle body injection," which is the simplest and cheapest form of fuel injection. That thing that looks like a carburetor on top of the manifold actually houses two fuel injectors, which feed all eight cylinders at the same time...like a carefully metered carburetor. It's not quite as efficient as "multi port fuel injection," which uses a separate fuel injector for each cylinder, but it's cheaper to manufacture. Why? Instead of using eight fuel injectors, you only need two. And it works very well.

TOM: Multi-port injection, as my brother said, has a separate fuel injector right at each cylinder. It tends to provide quicker throttle response than throttle body injection, because the fuel is delivered right to each cylinder, and doesn't have to work its way through the manifold to get there.

RAY: The next step up is "sequential, multi-port fuel injection." That's where you have an individual fuel injector for each cylinder, and the fuel is delivered at the precise instant the cylinder needs it. That's obviously the most sophisticated system, giving the best performance and the greatest increase in fuel economy. It's also the most expensive system.

TOM: But the truth is, throttle body fuel injection is good enough in most cases. It was a huge technological, ecological, "drivological" leap forward to go from carburetors to fuel injection. And improving on the specifics of fuel injection has led to more advances, but they've been marginal compared to the big leap.

RAY: The last comparable "big leap" my brother remembers was when they went from square wheels to round wheels on cars.

TOM: Yeah. And after that, radial technology was just gravy! 2392

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