Efi System; Efi System; Overview; Efi System Components - Toro Workman HDX Service Manual

EFI System

Overview

The electronic fuel injection system controls two as-
pects of engine operation: the amount of fuel delivered
to the engine and the amount of ignition timing advance.
The end result is seamless engine performance while
maintaining exhaust emission standards and maximum
fuel economy.

EFI System Components

Manifold Absolute Pressure (MAP) Sensor
The MAP sensor detects the amount of vacuum present
in the intake manifold at any given time. This sensor
uses the constant absolute pressure because it is not af-
fected by changing atmospheric conditions like normal
gauge pressure would.
The MAP sensor uses a 5V DC input reference and as
intake manifold pressure changes, it increases or de-
creases the amount of voltage returned to the ECU. The
ECU determines the engine load based on this return
voltage. The ECU can then regulate the proper amount
of fuel to be injected as well as selecting the most ap-
propriate ignition timing advance based on the engine
load.
Air Temperature Sensor
The function of the air temperature sensor is to provide
the ECU with instantaneous updates on the air tempera-
ture entering the intake manifold. The ECU can then
make small corrections based on certain temperature
ranges to increase or decrease the amount of fuel in-
jected above the base injection time. As air temperature
changes, so does air density. An example of this is when
air temperature increases; the amount of available vol-
ume of air in the intake manifold will decrease.
This decrease can cause a richer condition without the
ability to adjust for less dense air. The same could occur
with cooler dense air, resulting in a possible lean condi-
tion, as there is more oxygen available to the engine.
This sensor is a NTC (negative temperature coefficient)
type. At cold temperatures the NTC type sensor's resist-
ance is very high, but reduces as air temperature in-
creases.
Briggs/Daihatsu Gasoline Engine
The ECU (Electronic Control Unit) collects information
from various EFI system components to determine the
amount of compensation added to the base injection
time frame in the ECU's memory. This system ensures
the proper amount of fuel and ignition timing advance
delivered during various engine loads and RPM's. The
fuel injection time frame is synchronized to the intake
valve opening event for optimum engine efficiency.
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Figure 22
Figure 23
Workman HDX