SWAMP'S DIESEL PERFORMANCE & TECHNOLOGY

REVERSE ENGINEERING: 7.3l POWER STROKE INJECTOR DRIVER MODULE

 
Project Overview

Desoldering Components

IDM Models

Printed Circuit Board Details

Component Identification

Circuit Tracing & Component Symbols

Completed IDM Schematic

Sub-Circuit Analysis

Injector Waveforms

HIGH-PERFORMANCE IDM'S

IDM TESTING & REPAIR

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

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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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%

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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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

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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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.

 

 

 

 

 

 

 

 

 

 

 

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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

 

Graph 1

 

 

 

 

Graph 2

Graph 2 - Hi-Voltage IDM

 

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Graph 3

Graph 3 - Hi-Voltage Detail

Graph 4

Graph 4 - Hi-Voltage Detail

Graph 5

Graph 5 - Hi-Voltage Detail

Graph 6

Graph 6 - Hi-Voltage Detail

Graph 7

Graph 7 - Hi-Voltage Detail

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Graphs 8-12

Graph 8 - Hi-Voltage Detail

Graph 9 - Hi-Voltage Detail

Graph 10 - Hi-Voltage Detail

Graph 11 - Hi-Voltage Detail

Graph 12 - Hi-Voltage Detail

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Graph 13 (200 us time scale)

Graph 13 - Hi-Volt Hi-Freq Detail

Graphs 14-18 (50 us time scale)

Graph 14 - Hi-Volt Hi-Freq Detail

Graph 15 - Hi-Volt Hi-Freq Detail

Graph 16 - Hi-Volt Hi-Freq Detail

Graph 17 - Hi-Volt Hi-Freq Detail

Graph 18 - Hi-Volt Hi-Freq Detail

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Graph 19 (Before)

Graph 19 - Before Hi-Volt Hi-Freq Mod

Graph 20 (After)

Graph 20 -After Hi-Volt Hi-Freq Mod

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Graphs 21 & 22 (Before)

Graph 21 - Peak. Before Hi-Freq Mod

Graph 22- Gap, Before Hi-Freq Mod

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Graphs 23 & 24 (After Hi-Frequency Mod)

Graph 23 -After Hi-Freq Mod

Graph 24 -After Hi-Freq Mod

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Graphs 25 & 26 (Hi-Frequency + Hi-Voltage Mod)

Graph 25 -After Hi-Freq Hi Volt Mod

Graph 26 -After Hi-Freq Hi Volt Mod

Graph 27 -Detail After Hi-Freq Hi Volt Mod

 

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