Zamboni 445 - Engine Control Unit (ECU); Open Loop Versus Closed Loop Operation

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Ice Rink Air Quality
Engine Control Unit (ECU)
The ECU works to control the engine's air-fuel ratio (AFR) to the ideal levels based on the
engine's operating conditions. The ECU monitors the engine for speed, load, air and coolant
temperature and then adjusts the AFR via the electronic fuel injection to produce the ideal
mixture. If the AFR is near the ideal ratio (stoichiometric), then the catalytic converter
will operate at it's maximum efciency thus reducing the emission levels of the harmful
exhaust gases.
Typically, it takes a few minutes for the engine and catalytic converter to achieve proper
operating temperatures and conditions. Resurface only when the engine emission system
is up to normal operating temperature.
If the ECU detects conditions where it cannot control the AFR, it will then turn on the MIL,
thus alerting the operator. If the ECU detects that a portion of the engine equipment, which
it monitors, is malfunctioning, it will turn on the MIL. DO NOT OPERATE the machine
with the malfunction indicator light on continuously.
DANGER!
If the check engine light turns on during normal operation of the
machine, the machine must be serviced immediately!
Open Loop versus Closed Loop Operation
When the engine is rst started, it is operating in "open loop" condition. This means that the
ECU is controlling the AFR via pre programmed levels. When the engine achieves a certain
operating temperature, the ECU then goes into the "closed loop" mode. This means that the
ECU is controlling the AFR based on the engine operating conditions and is monitoring the
signal from the oxygen sensor to determine if changes to the AFR need to be made.
With the precise closed loop control of the AFR, the catalytic converter will be the most
effective in reducing the exhaust emission levels. The lowest levels of harmful emissions
are produced when the machine is operating in the closed loop mode. For this reason, start
the engine and warm it up in accordance with the starting instructions described on page
2-2. ONLY operate the machine on the ice when the engine emission system is up to normal
operating temperature.