Service Manual

4.11
ELECTRONIC FUEL INJECTION
4
The ECU controls the amount of fuel being injected and the
ignition timing by monitoring the primary sensor signals for air
temperature, barometric air pressure, engine temperature, speed
(RPM), and throttle position (load). These primary signals are
compared to the programming in the ECU computer chip, and
the ECU adjusts the fuel delivery and ignition timing to match
the values.
During operation the ECU has the ability to re-adjust
temporarily, providing compensation for changes in overall
engine condition and operating environment, so it will be able
to maintain the ideal air/fuel ratio.
During certain operating periods such as cold starts, warm up,
acceleration, etc., a richer air / fuel ratio is automatically
calculated by the ECU.
Initial Priming / Starting Procedure
NOTE: The injection system must be purged of all
air prior to the initial start up, and / or any time the
system has been disassembled.
If the EFI system is completely empty of fuel or has been
disassembled and repaired:
1. Cycle the key switch from “OFF” to “ON” 6 times,
waiting for approximately 3 seconds at each “ON” cycle to
allow the fuel pump to cycle and shut down.
2. Once step 1 is completed, turn the key switch to “START”
until the engine starts or 5 seconds has passed.
3. If the engine failed to start, repeat step 1 for 2 more cycles
and attempt to start the engine.
If the engine fails to start, a problem may still exist, and should
be diagnosed.
NOTE: Accurate testing of EFI components is
recommended utilizing the Digital Wrench™
Diagnostic Software (dealer only).
ELECTRONIC CONTROL UNIT (ECU)
Operation Overview
The ECU is the brain or central processing computer of the
entire EFI fuel/ignition management system. During operation,
sensors continuously gather data which is relayed through the
wiring harness to input circuits within the ECU. Signals to the
ECU include: ignition (on/off), crankshaft position and speed
(RPM), throttle position, engine coolant temperature, air
temperature, intake manifold air pressure and battery voltage.
The ECU compares the input signals to the programmed maps
in its memory and determines the appropriate fuel and spark
requirements for the immediate operating conditions. The ECU
then sends output signals to set the injector duration and ignition
timing.
During operation, the ECU continually performs a diagnostic
check of itself, each of the sensors, and system performance. If
a fault is detected, the ECU turns on the “Check Engine” light
in the speedometer and stores the fault code in its fault memory.
Depending on the significance or severity of the fault, normal
operation may continue, or "Fail-Safe" operation (slowed speed,
richer running) may be initiated. A technician can determine the
cause of the “Check Engine” light by initiating the “Blink Code”
sequence or by using Digital Wrench™. The ECU requires a
minimum of 7.0 volts to operate. The memory in the ECU is
operational the moment the battery cables are connected.
To prevent engine over-speed and possible failure, a rev-
limiting feature is programmed into the ECU. If the maximum
RPM limit (6500) is exceeded, the ECU suppresses the injection
signals, cutting off the fuel flow. This process repeats it self in
rapid succession, limiting operation to the preset maximum.
ECU