Efi Operation Overview; Efi Service Notes - Polaris ACE 900 2017 Service Manual

EFI OPERATION OVERVIEW

The EFI system is designed to provide peak engine performance with optimum fuel efficiency and lowest possible
emissions. The ignition and injection functions are electronically controlled, monitored and continually corrected during
operation to maintain peak performance.
The central component of the system is the Bosch ME17 Electronic Control Unit (ECU) which manages system
operation, determining the best combination of fuel mixture and ignition timing for the current operating conditions.
An electric fuel pump is used to move fuel from the tank, through the fuel supply line, to the fuel rail. Fuel pressure
regulators located in the tank and on the end of the fuel rail, maintain system operating pressure and return excess fuel
back into the fuel tank. At the engine, fuel fed through the fuel rail supplies fuel to the injectors, which inject into the
intake ports. The ECU controls the amount of fuel by varying the length of time that the injectors are "on." This range
can vary depending on fuel requirements. The controlled injection of the fuel occurs every other crankshaft revolution,
or once for each 4-stroke cycle. When the intake valve opens, the fuel/air mixture is drawn into the combustion
chamber, ignited and burned.
The ECU controls the amount of fuel being injected and the ignition timing by monitoring the primary sensor signals for
intake air temperature, manifold absolute pressure (load), engine temperature, engine speed (RPM) and throttle
position. These primary signals are compared to the programming in the ECU computer chip, and the ECU adjusts the
fuel delivery and ignition timing based on these 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.

EFI SERVICE NOTES

• For more convenient and accurate testing of EFI components, it is recommended dealers utilize the Digital Wrench®
Diagnostic Software (dealer only). Some testing may be done manually using the procedures provided in this
chapter.
• 80% of all EFI problems are caused by wiring harness connections.
• For the purpose of troubleshooting difficult running issues, a known-good ECU from another vehicle of the same
model and year may be used without damaging system or engine components.
• Never attempt to service any fuel system component while engine is running or ignition switch is "on."
• Cleanliness is essential and must be maintained at all times when servicing or working on the EFI system. Dirt, even
in small quantities, can cause significant problems.
• Do not use compressed air if the system is open. Cover any parts removed and wrap any open joints with plastic if
they will remain open for any length of time. New parts should be removed from their protective packaging just prior
to installation.
• Clean any connector before opening to prevent dirt from entering the system.
• Although every precaution has been taken to prevent water intrusion failure, avoid direct water or spray contact with
system components.
• Do not disconnect or reconnect the wiring harness connector to the control unit or any individual components with
the ignition "on." This can send a damaging voltage spike through the ECU.
• Do not allow the battery cables to touch opposing terminals. When connecting battery cables attach the positive
(red) cable to positive (+) battery terminal first, followed by negative (black) cable to negative (-) battery terminal.
• Never start the engine when the cables are loose or poorly connected to the battery terminals.
• Never disconnect battery while engine is running.
• Never use a battery boost-pack to start the engine.
• Do not charge battery with key switch "on."
• Always disconnect negative (-) battery cable lead before charging battery.
• Always unplug ECU from the wire harness before performing any welding on the unit.
9929422 R02 - 2017-2019 ACE 900 Service Manual
© Copyright Polaris Industries Inc.
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