Fuel Injector

Port injection sprays fuel into the intake ports; direct injection sprays it at high pressure into the combustion chamber. Diesels always inject directly. The control unit decides how long each injector stays open and, on direct injection, when. Injectors can clog, leak or stick. A leaking injector causes a rich mixture, hard hot starts or smoke; a clogged one causes a lean cylinder and misfire.

Port injectors spray fuel into the intake port in front of the valve; direct injectors spray straight into the combustion chamber at much higher pressure. Some engines combine both.

A solenoid or piezo element lifts the needle off its seat for a few milliseconds. Fuel pressure and opening time determine the amount injected. The control unit decides how long the injector stays open, called the pulse width. Diesel and some petrol injectors fire several times per cycle for quieter, cleaner combustion.

Injector faults cause misfires, rough idle, smoke and poor economy, with codes such as P0201 to P0208 or cylinder-specific misfire codes. Diesels may need injector coding after replacement. A leaking, sticking or clogged injector can cause misfires, rough idle, smoke, fuel smell and high consumption. Diesel injectors can often be tested by a workshop with a leak-off or balance test.