Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Fuel Injection System - Multi-Port: Description: Notes
The Port Fuel Injection (PFI) system is controlled by an on-board computer known as the Electronic Control Module (ECM). The ECM monitors engine operations and environmental conditions. The ECM output signals provide correct air/fuel ratio, ignition timing and idle speed.
Standard PFI systems feature simultaneous double-fire injection. Fuel rail, mounted to the intake manifold, provides fuel for the injectors. Fuel is constantly circulated through the rail during engine operation.
Injectors pulse once for each engine revolution, providing fuel directly to combustion chamber with precise timing. On Sequential Fuel Injection (SFI) models, injectors pulse sequentially in spark plug firing order. Differences between these systems are injector wiring and the ECM.
In all systems, constant fuel pressure is maintained to the injectors. Air/fuel ratio is adjusted by the time that injector stays open (pulse width). Various sensors provide information to the ECM to control pulse width. There are 2 major sub-systems; fuel system and electronic control system.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.