Fuel Injectors

A fuel injector is an electronically controlled nozzle that sprays fuel into the engine in a precisely measured amount. The PCM commands each injector to open for a specific number of milliseconds — called pulse width. A longer pulse width delivers more fuel. A shorter pulse width delivers less. The injector is either fully open or fully closed — it does not open partway. The amount of fuel delivered is controlled entirely by how long it stays open.

Port injection — PFI — sprays fuel into the intake port just upstream of the intake valve. The fuel mixes with air in the port and is drawn into the cylinder when the valve opens. Port injection operates at relatively low pressure — 40 to 60 PSI typically. Gasoline Direct Injection — GDI — sprays fuel directly into the combustion chamber at very high pressure — 500 to 3,000 PSI or more. Direct injection allows more precise fuel control and better fuel economy but requires a high-pressure fuel pump driven by the camshaft.

Clogged injector — the spray pattern is disrupted. Instead of a fine mist, the injector may drip or stream fuel. The affected cylinder runs lean. The PCM increases fuel trim to compensate. Leaking injector — the injector does not seal when closed and drips fuel into the cylinder. The affected cylinder runs rich. You may notice fuel smell or hard hot start because fuel puddles in the cylinder while the engine is off. Stuck open — the injector stays open continuously. The cylinder floods with fuel and the engine runs extremely rich on that cylinder.