Product Description Multec 3.5 Fuel Injector Application Manual
3-28 Delphi Energy and Chassis Systems
Revision: 11/05-1
− System voltage − System pressureError!
Bookmark not defined.
− Injector body temperature
(affects coil resistance)
− Wiring resistance and
connector resistance
− Fuel lubricity − Injector part-to-part tolerances
− Injector flow calibration − Driver characteristics
− Internal injector friction − Magnetic material properties
Injector flow deviates lean from the ideal linear line at very low pulse
widths due to the inability of the valve to open within the command pulse
time. Conversely, at very high pulse widths the injector has insufficient
time to close before the start of the next pulse and deviates rich from the
ideal linear flow line.
Additionally, injector opening and closing response times become less
repeatable at very low pulse-widths. As a result, fuel delivery also
becomes less repeatable. Refer to Figure 3-14 and Figure 3-15 for
graphical representations of high and low pulse-width flow effects.
Note:
The lowest useable pulse width is independent of injection frequency (or
engine rpm). The highest useable pulse width is a function of injection
frequency.
3.9.1 Minimum Pulse-Width (MPW)
Minimum pulse-width is the least amount of injector “on” time required to
achieve consistent fuel flow. During a single pulse event, the flow of an
injector does not stabilize until after the current rise-time effects are
complete. If the pulse time is less than an the opening event time,
inaccurate fuel flow results in the following ways:
• A lean shift occurs at low pulse-widths in the minimum pulse-width
region
• Flow rates in the minimum pulse-width region of the flow curve are
subject to larger pulse-to-pulse and part-to-part variations than in the
linear portion of the flow curve.
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