Section 4 Efi Engine Control Diagnostic Tests; Basic Efi Theory; Basic Open-Loop Theory; Engine Requirements - Generac Power Systems XT-EFI Series Manual

EFI Engine Control Diagnostic Tests
Section 4

Basic EFI Theory

Electronic Fuel Injection was first
automobiles in the late 1960s. EFI is not new, as its roots
were firmly established many years ago. However, EFI is
fairly new to portable generators.

Basic Open-Loop Theory

EFI uses a solenoid valve called an injector to meter fuel
delivery. The typical system uses 1 injector per cylinder.
When the solenoid is energized, fuel sprays out into the
intake valve port. Fuel is delivered to the injector by a
high-pressure electric pump at approximately 36 psi. Fuel
delivery is controlled by the injector which is cycled by
the ECU. The ECU (Engine Control Unit) produces a
signal to open the injector for a certain length of time
depending on engine conditions transmitted by the
sensors. The longer the injector is open, the more fuel is
injected. As engine load increases, the injector open time
is increased to match the increased airflow. This ECU
output signal is called the injector pulse width. The longer
the pulse width, the more fuel is injected. In a typical
Open-Loop EFI system, there is no oxygen (O
to monitor or change the fuel delivery.
G
A. Fuel Gauge / Float
B. Pressure Regulator
Diagnostic Repair Manual
introduced to
A B
Figure 4-1. Return-less System
C. Pressure Line
D. Fuel Injector

Engine Requirements

The correct proportion of fuel is required to be mixed with
the incoming air for efficient operation. Most generator
engines utilize a ratio of approximately 14.7 parts air to 1
part fuel for the no load to full load power band. This is
the chemically correct ratio which results in the lowest
average emissions and best power. A rich condition is
characterized by an excess of fuel and a lean condition is
characterized by an excess of air or lack of fuel.
As the load is increased, up to capacity, the throttle is
opened and as airflow increases fuel flow must increase
to match it.

Fuel System

See Figure
pump, regulator, and injector. Fuel is drawn from the tank
by the pump which steps up the pressure to
approximately 36 psi. Fuel pressure is controlled by the
fuel pressure regulator located in the fuel pump,
discharging unused fuel back into the tank. When load
demand increases, there is sufficient fuel available. The
) sensor
injector is sealed with an O-ring and has a 2-pin electrical
2
plug to carry switching current to the solenoid windings.
When energized, the solenoid core is pulled back,
allowing fuel to spray out in a fine, conical pattern.
F
E. Fuel Pump
F. Fuel Filter
4-1. EFI fuel systems consist of a tank,
C
E
G. Fuel Tank
D
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