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GMC Suburban:
Electronic Fuel Injection or Electronic Carburetor

By
Alex Steele
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seen in Truck Trend

Question:

 

I have a question about fuel injection. A friend and I were under the hood of his GMC Suburban while finishing up an oil change. We can't understand why it says EFI (Electronic Fuel Injection) when there is a carburetor sitting on top of the engine. I'm sure there's something obvious we're missing here, like an electronic carburetor.

 

Answer:

 

What you're looking at is a "throttle body" assembly. It does look very much like a carburetor until you remove the air cleaner and see the two big fuel injectors sitting on top. The throttle body injection setup was kind of a stage one in the world of fuel injection. It enabled the manufacturers to convert from a carbureted engine with as little change as possible.

 

The throttle body consists of two throttle plates which meter the air entering the engine as you depress the accelerator, along with the two injectors, a couple of sensors and an Idle Air Control valve to control idle speed. The whole package bolts on top of the intake manifold where the carburetor was positioned in the past.

 

What you expected to see under the hood of a fuel injected vehicle was "Port Fuel Injection". Port injection is the system which uses a fuel injector located at the intake port of each cylinder, just above the intake valve. As a spark plug fires for each cylinder, the injector pulses fuel. This surpasses the efficiency of throttle body injection by having an injector for each cylinder.

www.realworldautomotive.com

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GMC | Fuel Injection | Carburetor
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