See Figure 1
The EFI system can be broken down into three basic sub-systems; the fuel system, the air induction system, and the electronic control system.
The main components of the fuel system are the fuel tank, the fuel pump and the fuel injectors. The electric fuel pump supplies fuel from the tank, under a constant pressure, to the EFI fuel injectors. These injectors in turn dispense a metered quantity of fuel into the intake manifold in accordance with signals given by the Electronic Control Unit (ECU). Each injector is opened, at the same time, to introduce the fuel required for ideal combustion with each engine revolution.
The air induction system consists of the air cleaner, an air flow meter, an air valve and an air intake chamber. All of these components contribute to the supply of the proper amount of air to the intake manifold as monitored by the ECU.
The main component of the electronic control system is the ECU. The computer receives signals from various sensors indicating changing engine operating conditions such as:
These signals are utilized by the computer to determine the injection duration necessary for an optimum air/fuel ratio.
When there is a problem starting or driving a vehicle, two of the most important checks involve the ignition and the fuel systems. The questions most mechanics attempt to answer first, "is there spark-'' and "is there fuel-'' will often lead to solving most basic problems
Engine troubles are not usually caused by the EFI system. When troubleshooting, always check the condition of all other related systems, first.
The most frequent cause of problems with the EFI system is a bad contact in a wiring connector, so always make sure that the connections are secure. When inspecting the connector, pay particular attention to the following points:
- Check to see that the terminals are not bent.
- Check to see that the connector is pushed in all the way and locked.
- Check that there is no change in signal when the connector is tapped or wiggled.
If necessary, refer to Driveability & Emissions Controls for output of diagnosis codes and related service procedures