Fundamentals
Multec 3.5 Fuel Injector Application Manual
2-28
Delphi Energy and Chassis Systems
Revision: 11/05-1
Voltage Sensitivity/ Offset Used to adjust the flow curve to account for system voltage
variation
Vacuum Effects
Typically used for non-vacuum biased systems, such as returnless
fuel systems. Compensates for flow shifts as manifold vacuum
changes. Delphi can provide slope & intercept values for each
vacuum point of relevance to the customer.
Fuel Pressure Sensitivity
Typically a function of regulator gain. Can be minimized by using
rail flow data for recirculating systems. For Demand fuel systems
Delphi normally provides flow data at a constant rail fuel pressure.
Any regulator gain correction must be done as part of the fuel
pump correction.
Temperature Sensitivity
Usually applied as an offset to the base fuel flow curve, if
required.
Low Pulse Width
Correction
As the injector operates at very small pulse widths, the actual flow
curve will deviate from the linear regression predicted flow.
Although Multec 3.5 maintains linearity to very low pulse widths,
some applications may still require low pulse correction.
Injector-to-Injector
Variation
Multec 3.5 Fuel Injectors are manufactured to very tight
tolerances. Using rail calibration flow data will further help
minimize the effects of individual injector variation by averaging
the injector flows.
Pulse-to-pulse repeatability Typical calibration flows are provided as the average of several
data points at a given pulse width to minimize any pulse to pulse
issues.
Durability Shifts
The fuel system may be required to compensate not only for
internal shifts, but also for shifts in other parts of the engine. This
is typically done by ensuring enough dynamic range exists in the
closed-loop feedback control of the fuel system.
Fuel Properties
Consideration must be given to the types of fuel the vehicle might
be exposed to over the life of the vehicle. Differences in the
distillation curves, volatility, specific gravity, etc. will impact the
flow curve. The type of fuel that the injector calibration data is
generated from will need to be considered based upon customer
requirements.
If the vehicle is designed to operate on fuels with high alcohol
fuel content, increases to the commanded injector pulse width
must be made to account for the lower energy content of the
alcohol fuels. (See sections 2.2.1.1 and 3.6.4)