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4.2.3 LS 1-4 Tab
The purpose of the PFI LS 1-4 tab is to enable individual PFI Driver lowside (LS) channels 1-4, and configure their
Pulse Width Modulation (PWM) parameters. Each LS channel is capable of 1.5A continuous. A special mode of
operation is provided to combine current drive capacity among pairs of channels. LS channels one and two can
be locked together to provide up to 3A current drive capacity. Likewise, LS channels three and four can be locked
together to provide 3A current drive capacity. When channels are locked together, they operate in lock-sync with
each other. When channels one and two are locked together, the PWM parameters for channel one are commanded
to both channels one and two. When channels three and four are locked together, the PWM parameters for channel
three are commanded to channels three and four.
Channels one and three of the Lowside channels on the first PFI Module are also provided special modes of
operation for common rail diesel fuel pressure control. It is typical that common rail diesel fuel systems have high
pressure pumps with Inlet Metering Valves (IMV) which are proportional solenoid valves requiring PWM operation to
control rail pressure by regulating the inlet fuel flow to the pump. Common rail diesel fuel systems may also have a
High Pressure Valve (HPV) as a bleed valve on the fuel rail. These valves also require PWM operation to control the
pressure bleed rate to return fuel to the tank. Channels one and three are provided with mode selectors to operate
as IMV or HPV controls. It is typical that IMV and HPV solenoids require up to 3A current drive. Therefore, it is
recommended that channel one be locked with channel two when operating as IMV or HPV control. Likewise, it is
recommended that channel three be locked with channel four when operating as IMV or HPV control.
When channel one or channel three is configured for IMV or HPV control, then the Rail Pressure Control Setup
window should be configured to implement PID control of common rail pressure using those channels.
There are no dedicated IMV or HPV control modes available on the Lowside channels on the second PFI Module.
Only generic PWM parameters are available on PFI2 (LS1-4) tab . LS channels one and two and LS channels three
and four can still be locked together to supply up to 3A current drive much like the first PFI Module .