fuel is injected into the intake port and mixed with air while the air-fuel mixture is drawn into the cylinderChecked 2026-08-12
Port fuel injection (PFI)
A fuel system that sprays petrol into the intake port, upstream of the cylinder.
Also called: PFI · port injection · multiport injection · MPI
What it means
Definition
The DOE describes the conventional arrangement: fuel is injected into the intake port and mixed with air while the air-fuel mixture is drawn into the cylinder. This was the standard method before direct injection spread. Some engines now run both, with port injectors alongside direct injectors.
Why a buyer cares
What it changes
Fuel passing through the port washes the back of the intake valve. SAE research names the absence of that fuel-washing process in direct-injection engines as why deposits accumulate there.
In practice
Where you meet it
In engine spec lines as PFI or MPI, mostly on older cars and on engines that pair both injection types.
Two things that look alike
Not the same as
Direct injection sprays into the cylinder; port injection sprays before it. Dual-injection engines do both.
Read next
Related terms
Where it shows up
Related problem files
Where this comes from
Sources
Due to the lack of a fuel-washing process that is typical of Port Fuel Injected (PFI) enginesChecked 2026-08-12
Only the SAE abstract is free; the full paper is paywalled — say so where the site cites it. No citable definition of dual injection was found.