| Technical
literature often refers to the Power Stroke as using 115
VDC to operate the injectors, while I refer to it as
being 110 V. This is mostly a case of others rounding up
and me rounding down, but it also depends somewhat on
where and when you measure the voltage, too. The
oscilloscope graphs in the previous section (Injector
Waveforms) were all taken on stock, unmodified IDMs.
Now we look at modified ones. This is the same IDM
and injector as shown in graphs 13-18 in Injector
Waveforms, and Graph 13 is shown again to the right.
The so-called "High Voltage" modification consists of
changing the feedback resistor in the power supply,
which increases the output voltage from 110 to 135-140
volts.
If you keep the resistance in a circuit constant, and
increase the voltage, the current flow will increase.
This increased current builds up a stronger magnetic
field in the solenoid, and it builds more quickly. This
in turn opens the injector faster, and holds it open
more firmly through out the firing cycle.
(Graph 2) After modifying the IDM, the waveform
looked like this. The increased voltage is evident by
the increased height of the pulses in both the peak and
the hold portion of the pulse, although the peak pulse
decreased to .38 ms, a decrease of 24%. The first
gap in the pulse is still about .40 ms, but the second
gap has increased slightly, and the hold pulses after
the first gap are farther apart.
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Graphs 3-8 are 5 consecutive frames taken with the
same IDM on the same injector as graph 1 & 2, but before
modifying it. The time scale has been changed from 200
micro-seconds down to 50 to get a detail view of the
hold pulses. The entire screen here corresponds to the
2-1/2 squares on the right in the previous graphs.
Although the pulse spacing is somewhat erratic,
measuring from the rising edge of first full pulse on
the screen and counting 5 pulses, gives the following
info:
| Avg Pulse Spacing: 69 us |
| Avg Pulse Width: 12 us |
| Avg Time Betwen Pulses: 57 ms |
| Avg Pulse Duty Cycle: 17.3% |
| Avg Pulse Frequency: 14.45 kHz |
------------------------------------------------
Graphs 8-12 shows the waveforms after doing the
Hi-Voltage Mod to the IDM.
| Avg Pulse Spacing: 74 us |
| Avg Pulse Width: 10 us |
| Avg Time Betwen Pulses: 64 ms |
| Avg Pulse Duty Cycle: 13.5% |
| Avg Pulse Frequency: 13.50 kHz |
The IDM responded to the increased current draw
caused by the higher voltage by decreasing the pulse
width 17% and the frequency 7%, which in turn decreased
the duty cycle by 22%
-----------------------------------------------
Swamp's
HI-Voltage / Hi-Frequency IDM's
To compensate for this reduction in duty cycle, we
have developed a completely new modification,
which increases the pulse width and the frequency,
thereby increasing the duty cycle of the hold pulse, and
drastically reducing the length of the big gap in the
hold pulse, too.
(Graph 13 ) Whereas the Hi-Voltage Mod
caused the peak pulse to get shorter, the Hi-Frequency
Mod returns it to .48 ms, almost its original length of
.50 ms. The first gap has decreased from .40 ms to .22,
the second gap also cut by half to .10 ms, and the hold
pulses are visibly closer.
This can be seen in more detail in Graphs 14-17; when
comparing these to the previous ones, it will be seen
that the pulses are closer together, and equally
important, they are much more uniformly spaced.
| Avg Pulse Spacing: 70 us |
| Avg Pulse Width: 12 us |
| Avg Time Betwen Pulses: 58 ms |
| Avg Pulse Duty Cycle: 17.1% |
| Avg Pulse Frequency: 14.30 kHz |
-------------------------------------------------
Other IDM's before and after Swamp's Hi-Frequency
Modification.
In Graphs 19 & 20, the gap from an IDM that already
has the Hi-Voltage Mod is reduced from .54 ms to .20 ms
after the Hi-Frequincy Mod.
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Graphs 21 & 22 Pulse peak is .50 ms and the gap
is .42 ms
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Graphs 23 & 24 are after doing just the Hi-Frequency
Modification. The peak is now .64 ms, and the gap has
dropped from .42 to to .30 ms, but the voltage at the
end of the peak has dropped to 80 volts.
------------------------------------------------
In Graphs 25 & 26, the IDM has been given the
Hi-Voltage Mod. The peak is now .47 ms and the voltage
at the end of the peak, and through out the hold pulse,
is about 110 volts and the gap is even shorter-- down to
.24 ms-- almost half of what it originally was.
Zooming in on the hold pulse shows very uniform and
consistent pulses and gives the following stats:
| Avg Pulse Spacing: 70 us |
| Avg Pulse Width: 14 us |
| Avg Time Betwen Pulses: 56 ms |
| Avg Pulse Duty Cycle: 20.0% |
| Avg Pulse Frequency: 14.30 kHz |
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