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1993 GMC Intake

I was changing the air filter on a 1993 GMC Sierra Pickup with the 4.3 engine and noticed a pipe connecting the heat shielding from the exhaust manifold to the air intake plumbing. It seems like it is routing hot air from the exhaust directly into the intake system. Why would this be done, it seems a little counter intuitive?

There is a damper in the air cleaner assembly to redirect hot air (not exhaust) heated by the exhaust manifold for better driveability when the engine is first started.

Ed B.

That makes perfect sense, but because that circuit never “shuts off” wouldn’t that reduce power once the engine is up to temperature?

There is almost always some means of regulating the temperature of the intake air. There is a control system there somewhere.

“Carb heat” is usually not needed for summer driving. (I realize it’s fuel injected) but it makes a big difference in the wintertime…

Once the engine warms up the damper closes and only cold air enters the TBI.

Ed B.