Volume 1
DIESEL CAM TIMING For 6.0L, 4.5L, and 6.4L engines
Guide for using the IDS Oscilloscope
Diesel Cam Timing
Table of Contents
Overview 5
S E T U P
6.0L Light Duty Applications 7
Connection Scheme 10
Hookup with BOB 12
Hookup without BOB 15
Oscilloscope Settings 17
Retrigger 19
6.0L DIESEL RELATIVE CAM TIMING DIAGNOSTIC THEORY
Engine Component Location 21
Front of Engine Wire Frame Drawing 22
Good Pattern with Labels 26
WAVEFORM EXAMPLES OF CORRECT CMP-TO-CKP TIMING (6.0L)
Retrigger 28
CMP Only 29
CKP Only 30
CMP and CKP Together 31
Good Pattern with Instructions 32
Looking at Complete Trigger Wheel 34
6.0L WAVEFORM EXAMPLES OF INCORRECT TIMING CONCERNS
CKP Retarded 36
CKP Advanced 37
6.0L WAVEFORM EXAMPLES OF OTHER CONCERNS
Damaged CKP Trigger Teeth 40
Wrong Coupling Setting 42
Reversed Polarity 43
Ground Connection Problems 46
DC Voltage Shift 50
Weak Amplitude 51
MONITORING CMP AND CKP WITH PCM CONNECTED
Settings and Connections 52
MONITORING CMP-O AND CKP-O
Settings and Connections 57
CMP–to–CMP-O Relationship 59
CMP-O-to-CKP-O Relationship 60
CKP-to-CKP-O Relationship 62
ADVANCED APPLICATION
TDC Locations on CKP Trigger Wheel 63
Explanation of CKP Tooth Count 66
Tooth Orientation on Oscilloscope 67
CMP Signal Relationship 68
CKP Signal Relationship 69
Circuit Bias Voltage 71
6.0L F-650/750 SUPPLEMENT
Hookup 74
333 4.5L LOW CAB FORWARD SUPPLEMENT
Early LCF (2006-2007) Hookup 75
Late LCF (2008+) Hookup 76
Theory and Example Waveform 77
6.4L SUPPLEMENT
Hookup 81
Example Waveform 82
TABLE OF ACRONYMS AND TERMS
List 84
444 Overview
This procedure is designed to verify whether a relative cam timing concern exists by monitoring the CMP-to-CKP signal relationship with the oscilloscope.
Use this procedure to diagnose concerns related to the PCM Datalogger PIDs "SYNC" and "FICM SYNC" reading "No" or whenever a concern is suspected with the CKP or CMP inputs to the PCM. Symptoms such as crank/no-start, repeated crank/start/stall with excessive white exhaust smoke and muffled combustion noise, rough run with low contribution from paired/companion cylinders in the firing order, erratic RPM PID or tachometer readings, and lack of power may be associated. DTCs associated with CMP and CKP signals may be present as well.
By using the oscilloscope, the following can be identified:
-base engine cam timing concern
-CKP trigger wheel out of position (slipped) on crankshaft
-missing or noisy CMP and CKP signals
-variations in sensor-to-trigger tooth air gap (bent or damaged trigger wheel)
This document was written in detail for 6.0L light duty applications. Much of the information will be useful for the 4.5L and 6.4L, however, if the vehicle being serviced is an F-650/750 truck with 6.0L engine, a 4.5L Low Cab Forward, or a 6.4L F-series application, refer to the appropriate supplement for specific hookup illustrations and waveform examples.
Follow the instructions on the hookup screen to make the necessary electrical connections. Refer to the Setup portion of this document for more details.
The primary goal of this procedure is to determine if the CMP and CKP signals are in the proper relationship to one another. To learn the basics about what the CMP and CKP sensor signals should look like and what to expect from the oscilloscope while performing this procedure, refer to the Diagnostic Theory portion of this document.
Compare the waveforms captured on the vehicle to the document sections titled Waveform Examples of Correct CMP-to-CKP Timing, Waveform Examples of Incorrect CMP-to-CKP Timing, and Waveform Examples of Other Concerns.
In special circumstances, it may be necessary to measure the CMP and CKP signals while cranking with the engine harness connected to the PCM. Refer to Monitoring CMP and CKP with PCM Connected for unique settings and connection methods to properly perform this.
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If a concern is suspected with only the CMP-O or CKP-O signals, refer to the section titled Monitoring CMP-O and CKP-O.
The Advanced Application portion of the document offers detailed information to help get the most out of this procedure.
666 Setup Setup (for 6.0L light duty applications)
Use of the 46 pin adapter with overlay (Rotunda tool NUD105-R0107) and the 104 pin break out box offer the simplest means of connecting the oscilloscope to the necessary circuits.
Without a break out box, it is still possible to connect to the necessary circuits using the flex probes called out in the appropriate hookup illustration. These flex probes are part of the VMM kit.
It is also necessary to use jumper wires to connect the CKP- and CMP- circuits to battery negative during this procedure. Fused jumper wires with standard size stackable banana plugs are recommended. These may be fabricated or obtained locally.
Begin by fully charging the vehicle's batteries prior to carrying out the rest of this procedure. If the batteries are weak, it becomes much more difficult to capture a useable waveform.
For this procedure it is necessary to use a separate battery from the vehicle to power the VMM. One of the two vehicle batteries may be used for this purpose so long as the battery cables are disconnected to isolate it from the vehicle's electrical system. (The engine will still crank with one battery as long as the battery is in good condition.)
In the case of F-series/Excursion, it is necessary to remove the left side battery cables to remove the battery cover and gain access to the PCM. This makes the left side battery a convenient choice for the VMM power supply. Be sure to insulate the disconnected positive battery cable end to prevent a short to ground.
If isolating one vehicle battery is not feasible, a booster battery or jump box may be used for the VMM power supply instead.
In all cases the CMP- and CKP- circuits must be connected to the same negative battery terminal as the VMM.
Gain access to the engine harness connector of the PCM. The engine harness connector is the middle connector on the PCM. (See figure 3.) This procedure is intended to be performed while the engine harness connector remains unplugged from the PCM. This serves both as an access point for making connections and as a means of preventing the engine from starting while cranking. (The engine will still crank with the middle connector of the PCM unplugged, but will not crank if either of the other connectors are unplugged.)
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Figure 3
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Review the wiring diagram of the CKP and CMP circuits in figure 4 below.
Figure 4
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The connection scheme is illustrated in figure 5.
Figure 5
The PCM engine harness connector face illustration has been included for reference in figure 6.
Figure 6
The red probe routes the CKP+ signal to oscilloscope channel 1 which appears as the yellow trace on the screen. The black probe routes the CMP+ signal to oscilloscope channel 2 which appears as the red trace on the screen. CKP- and CMP- are connected to the same battery negative as the VMM (battery cable A-401) to assure a common electrical ground reference. Refer to figure 7 or 8 for a review of the hook up graphic. The illustration and instructions for making connections with the Break Out Box are given first. The instructions for making connections without the Break Out Box are give later.
Figure 7 is 6.0L Light Duty BOB Hookup
Hookup Instructions when using BOB (Figure 7)
1. Fully charge the vehicle's batteries.
2. Provide an isolated battery as a power source for the VMM by using method A or B.
A. Isolate one of the vehicle's batteries by disconnecting the cables from its terminals. B. Use a separate battery (booster battery or jump box).
If one of the vehicle's batteries is to be used, insulate the disconnected positive battery cable end with a shop towel or other means to prevent a short to ground.
3. Connect the 46-pin adapter (NUD 105-R0107) to the 104-pin Break Out Box (BOB) as shown.
Disconnect only the engine harness connector (middle connector) of the PCM. This connector will remain unplugged during this procedure.
Connect the 46-pin adapter to the engine harness. Do not connect the adapter to the PCM for this procedure.
Put the 46-pin overlay on the 104-pin BOB.
4. Connect the red roving probe (C-403) to the CKP+ signal and black roving probe (C-402) to the CMP+ signal by using the vehicle wiring diagram with the appropriate overlay on the BOB.
5. Connect the power supply cable (A-401) of the VMM to the isolated battery described in step 2.
6. Using fused jumper wires, connect the CKP- and the CMP- circuits to the same negative battery terminal as the VMM black alligator lead.
7. This procedure will be performed while cranking the engine for approximately 5 seconds. Make sure all cables and tools are clear of moving engine components prior to cranking the engine.
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8. When ready, select the tick, wait for two seconds, and then crank the engine until the oscilloscope displays a consistent waveform. Do not crank the engine for more than 15 seconds. Refer to the waveform examples later in this document for more information about interpreting results.
141414 Figure 8 is 6.0 L Light Duty Hookup without BOB
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Hookup instructions without BOB (Figure 8)
1. Fully charge the vehicle batteries.
2. Provide an isolated battery for the VMM by using method A or B.
A. Isolate one of the vehicle's batteries by disconnecting the cables from its terminals. B. Use a separate battery (booster battery or jump box).
If one of the vehicle's batteries is to be used, insulate the disconnected positive battery cable end with a shop towel or other means to prevent a short to ground.
3. Disconnect only the engine harness connector (middle connector) of the PCM. This connector will remain unplugged during this procedure.
4. Connect the red roving probe (C-403) to the CKP+ signal and the black roving probe (C-402) to the CMP+ signal using the purple colored flex probes (T-013).
5. Connect the power supply cable (A-401) of the VMM to the isolated battery described in step 2.
6. Use the two universal probes (T-015) of the VMM kit to probe the CKP- and CMP- terminals of the engine harness connector. Connect these circuits to the same battery negative terminal as the VMM black alligator lead. Use fused jumper wires and the black alligator clip (T-019). Fused jumper wires with stackable banana plugs may be fabricated or obtained locally.
7. This procedure will be performed while cranking the engine for approximately 5 seconds. Make sure all cables and tools are clear of moving engine components prior to cranking the engine.
8. When ready, select the tick, wait for 2 seconds, and then 161616 crank the engine until the oscilloscope displays a consistent waveform. Do not crank the engine for more than 15 seconds. Refer to the waveform examples later in this document for more information about interpreting waveforms.
The proper oscilloscope settings for measuring relative cam timing while cranking will be made automatically when the hookup method is selected on IDS. If it is necessary to manually select the oscilloscope settings, use the following guide.
Oscilloscope settings for measuring CMP and CKP while cranking with PCM disconnected
Channel 1 (will be CKP signal) Manual Sense - Red Probe Scale - 500 mV per division Coupling - DC Filter - None Invert - Off Display - On
Channel 2 (will be CMP signal) Manual Sense - Black Probe Scale - 200 millivolts per division Coupling - DC Filter - None Invert - Off Display - On
Time Base 20 milliseconds per division
Trigger
171717 Source - Channel 2 Edge - Rising Mode - Normal
Trigger position settings: Vertical +3 divisions (0.6 volt) Horizontal 2 divisions (40 milliseconds)
Set the screen display to full screen mode (square within a square icon at lower right) for best viewing.
Press the red man icon to begin acquisition. The oscilloscope will wait for a valid trigger before displaying any data.
Connect the: Red probe to pin 30 Black probe to pin 31 pins 41 and 43 to same ground point as VMM negative battery lead
Check the connections and then set the trigger mode to auto if no pattern is displayed while cranking.
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When releasing the ignition key, the oscilloscope may re-trigger if the peg on the camshaft happens to pass by the CMP sensor one more time before the camshaft stops turning. The waveform captured in this scenario will look similar to figure 9 below. If this happens, try cranking the engine again. If the issue persists, crank the engine and then press the green running man on the screen to stop acquisition while a valid waveform is being displayed.
Figure 9
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While using the oscilloscope in this procedure, the trigger has been automatically preset to trigger off of the CMP pulse (channel 2). A missing or weak CMP signal may prevent the oscilloscope from displaying a waveform.
If no waveform is displayed after 10 seconds of cranking, stop and check all connections. Change the screen display from wide screen to standard size in order view the menu. The button in the lower right hand corner of the screen that appears to be a square within a square changes the screen display size. From the oscilloscope menu, select Trigger and change the trigger mode from Normal to Auto. Refer to figure 9 for a screen image showing the controls mentioned here.
Try cranking again while watching the screen. If the CMP signal is missing or very weak compared to the following example waveforms, diagnose the circuit or sensor concern first. Remember to return the trigger mode to the normal setting prior to continuing with the oscilloscope.
Note: It is critical that all of the electrical connections be completed as illustrated in the hookup screen and explained here. Failure to do so can result in false readings!
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6.0L Diesel Relative Cam Timing Diagnostic Theory Prior to viewing the oscilloscope waveform, it is important to review what the expected output from the CMP and CKP sensors should be. Figure 10 illustrates the basic layout of the crankshaft and camshaft within the engine block. Note that the timing gears are at the rear of the engine.
Figure 10
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Figure 11 is a frontal view of the engine. The front cover has been removed. This drawing is meant to show how the CMP and CKP sensors are positioned inside the engine block. The CKP trigger wheel is physically inside the engine block and is not accessible simply by removing the front cover.
Figure 11
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Refer to figure 12 while reviewing the following description:
The CMP sensor generates a single pulse once per camshaft revolution. A peg pressed into the camshaft causes the CMP sensor to generate a signal as the peg passes the sensor tip.
The CKP sensor generates 58 pulses per crankshaft revolution. The CKP signal is produced in relation to a trigger wheel having a tooth pattern of 60 minus 2. The area on the CKP trigger wheel where the 2 consecutive teeth are absent generates a unique pulse once per crankshaft revolution. The CKP trigger wheel is pressed onto the crankshaft and held in location by a retaining pin.
Figure 12
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There is a fixed relationship (in degrees of crankshaft rotation) between the CMP pulse and the unique CKP pulse (caused by the minus 2 teeth area). This relationship can only change if base engine cam timing changes or if the CKP trigger wheel moves out of position on the crankshaft.
This procedure is designed to measure the relationship between the CMP pulse and the unique CKP pulse (from the minus 2 teeth area). Measuring this relationship on a concern vehicle and comparing the waveform with examples of a known good engine shown later in this document or on a known good vehicle will allow a determination to be made whether relative cam timing is the source of the vehicle's concern.
By counting the number of negative CKP pulses on the captured waveform between the CMP pulse and the CKP minus 2 teeth area, the relative cam timing can be measured. More detail about this will be provided below.
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Figure 13 is an illustration of a waveform from a properly timed 6.0L engine. The CKP signal is yellow (channel 1) and the CMP signal is red (channel 2). The CMP and CKP electrical signals appear in the same relationship as the physical engine parts illustrated in figure 11 and figure 12. Labels will appear later on this same waveform for clarification.
Figure 13
While interpreting the waveform for CMP-to-CKP timing it is important to remember the following:
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From the minus 2 teeth area of the CKP signal, count each negative CKP pulse (going from right-to-left) until reaching the point where the CMP waveform (falling edge) crosses the 0 axis.
The falling edge of the CMP signal should cross the 0 axis within the negative portion of 11th tooth pulse to the left of the CKP minus 2 teeth area. This is illustrated in figure 14.
Figure 14
Additional information related to the CMP and CKP signals can be gathered with the oscilloscope at the same time by studying the waveform.
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Missing, erratic, or excessively noisy signals can easily be seen as the waveforms appear on the screen. Additional information will be provided with example waveforms later in this document.
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Waveform Examples of Correct Cam-to-Crank Timing (6.0L) Waveforms of correctly timed engines are given here for reference. If the oscilloscope is not displaying any waveform, refer back to the Setup portion of the document for help to verify proper connections prior to proceeding.
Figure 15 is an example of the oscilloscope re-triggering as the engine stops turning. If this type of pattern appears, crank the engine again and capture a waveform that appears while the engine is at cranking speed. Re-triggering happens at random. If re-triggering persists, simply press the green running figure icon while cranking the engine to capture a waveform manually.
Figure 15
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A normal CMP signal is shown alone in figure 16. Figure 16
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The CKP signal is featured alone in figure 17. Note the appearance of the minus 2 teeth area which is circled. Also, notice how the amplitude of the CKP pulses vary. This is normal while cranking.
Figure 17
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A properly timed engine free of sensor or circuit concerns will produce a pattern as illustrated in figure 18.
Figure 18
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As discussed in previous portions of this document, the critical information in the waveform is the number of negative CKP pulses between the CKP minus 2 teeth area and the CMP falling edge 0 axis crossing. Figure 19 is a captured waveform with labels to clarify this. Note the minor imperfections and noise on the CMP waveform. This is normal.
Figure 19
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Figure 20 is a saved waveform which has been labeled in a similar fashion. For clarity of illustration, the time base was set to 10 ms per division, channel 1 voltage set to 1 volt per division, and cursors A and B were used to mark the beginning and end of the 11th CKP tooth.
Figure 20
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Once the CMP-to-CKP timing relationship is verified, inspect the rest of the CKP pattern for evidence of damaged teeth or other concerns. To do so, change the time base from the oscilloscope menu to 50 ms per division, change the display to wide screen mode, and capture another waveform while cranking. An example of a good waveform is shown in figure 21. Note how the CKP waveform amplitude varies as each of the cylinders goes through a compression stroke. For more information about how the individual cylinders could be identified in this waveform, refer to the Advanced Application section of this document.
Figure 21
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Waveform Examples of Timing Concerns Waveforms showing examples of the following concerns are included in this section:
-CKP retarded relative to CMP (CKP trigger wheel slipped or incorrect base engine timing)
-CKP advanced relative to CMP (cam gear slipped, incorrect base engine timing, or CKP trigger wheel slipped)
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If the CKP trigger wheel has slipped on the crankshaft, it may result in a pattern similar to figure 22. When the CMP falling edge 0 axis crossing shifts to the left as illustrated, the CKP signal is retarded from (or behind) the actual crankshaft position. This signal will result in the injection timing being late or retarded. This signal could also be caused by the cam and crank gears being out of time. If the CMP falling edge 0 axis crossing is out of place by more than 1 CKP pulse as illustrated here, there is a relative cam timing concern that requires inspection of internal engine components. Figure 22
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A timing concern in the opposite direction (CKP advanced relative to CMP) is shown in figure 23. This may be the result of the cam gear slipping on the camshaft, incorrect base engine timing, or possibly a CKP trigger wheel that has slipped. If the CMP falling edge 0 axis crossing is out of place by more than 1 CKP pulse as illustrated here, there is a relative cam timing concern that requires inspection of internal engine components.
Figure 23
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Figure 23A is an example from an engine where the CKP trigger wheel slipped a significant amount (crank/no-start).
Figure 23A
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Waveform Examples of Other Concerns
Waveforms showing examples of the following concerns are included in this section:
-damaged teeth on CKP trigger wheel (Figure 24)
-noisy signals (Figure 25)
-reverse polarity (Figures 27-29)
-CMP- and CKP- not properly grounded (Figures 30-33)
-DC offset (Figure 34)
-weak signal (low amplitude) (Figure CMP not fully seated)
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Damaged teeth on the CKP trigger wheel are illustrated in figure 24. Damaged teeth will consistently produce an abnormal signal when compared to other teeth on the CKP trigger wheel. A damaged tooth on the CKP trigger wheel will affect two cylinders (paired cylinders in the firing order). Symptoms such as rough run at certain engine speeds, erratic tachometer or RPM PID readings, or buck/jerk may result.
Figure 24
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Figure 25 is an example of excessive noise, especially on the CMP circuit. This can be caused by CMP- or CKP- circuits being jumpered or shorted to ground while the engine harness is connected to the PCM. For information about why this is the case, refer to the Advanced Application section of this document. If the PCM engine harness connector must remain connected to the PCM, refer to the document section, Monitoring CMP and CKP with PCM Connected, for the proper measurement technique.
Figure 25
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If the channel coupling is accidentally changed to AC on channel 2 (CMP), the waveform will be distorted as shown in figure 26. Because of the CMP waveform distortion, the CMP falling edge 0 axis crossing appears out of time, but the engine has no actual concern. Verify that the CMP channel coupling is set to DC.
Figure 26
Examples of reversed polarity are shown below. Verify all connections are correct and recheck the waveform before diagnosing the wire
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Figure 27 indicates that the CMP polarity is reversed. No changes were made to the trigger settings. That is why a portion of the up-side-down CMP waveform is beyond the left edge of the screen. Note that the CMP signal 0 axis crossing (now the CMP rising edge) is still at the same place on the CKP waveform (11th negative CKP pulse to the left of the minus 2 teeth area. Compare to previous waveforms for reference.
Figure 27
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Figure 28 indicates that the CKP polarity is reversed.
Figure 28
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Both CMP and CKP have reversed polarity in figure 29.
Figure 29
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Faulty connections will also cause peculiar waveforms. Again, check all measurement connections before going farther.
The CMP- was not grounded to the same point as the VMM negative battery lead in figure 30.
Figure 30
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In figure 31 the CKP- was not grounded to the same point as the VMM negative battery lead. Note how the amplitude has been reduced and that the most distorted portion of the waveform is the minus 2 teeth area.
Figure 31
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If CMP- and CKP- are connected together, but not to ground, the waveform of figure 32 will appear.
Figure 32
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Figure 33 is an example of the CMP- and CKP- signals having been connected to a different battery negative which is not shared by the VMM.
Figure 33
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DC offset is illustrated in figure 34. Note how the CMP waveform has shifted downward as indicated. This caused the CMP falling edge 0 axis crossing point to shift to the left. This could lead to misdiagnosis. The abrupt electrical load of the starter can result in DC offset. Be sure the VMM is powered from a battery not connected to the starter.
Figure 34
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Excessive air gap caused the CMP signal to be weak in the next figure. Rust on the engine block surface prevented the CMP sensor from fully seating. Figure CMP not fully seated
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Monitoring CMP and CKP with PCM Connected
If it is necessary to monitor CMP and CKP with the PCM connected (especially while cranking), use the following information to make the necessary connections between VMM and the Break Out Box and to set up the oscilloscope.
The CMP signal will need to be measured as a differential input using the red probe on CMP+ and the black probe on CMP-. Channel 3 will be the input for the CKP+ signal. Use an ignition transducer cable (C-404) and connect lead A to the CKP+ circuit using adapter T-017. Refer to the illustration on the next page.
The CKP- should be disconnected from battery negative.
The VMM should no longer be powered by an isolated battery. Restore the vehicle battery connections if one battery was previously isolated and connect the VMM to a vehicle battery for its power supply.
Remove the FICM relay to prevent the engine from starting and disconnect the glow plug module to reduce current consumption while cranking.
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6.0L Light Duty Hookup for Monitoring CMP and CKP with PCM Connected
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The following oscilloscope settings should be used (intended for cranking speeds)
Channel 1 (CMP signal) Manual Sense - Red and Black Probe - Diff. Scale - 200 mV/div Coupling - DC Filter - none or 1.3 kHz Invert - Off Display - On
Channel 3 (CKP signal) Manual Sense - Ignition A Scale - 200 mV/div Coupling - AC Filter - none Invert - Off Display - On
Time Base Scale - 20 ms/div Zoom - 100%
Trigger Source - Channel 1 Edge - Rising Mode - Normal
Select the trigger control button next to the yellow number 1 button on the lower edge of the screen. Use the directional arrows to position the vertical trigger position at 0.6 volt (3 divisions above 0 and the horizontal trigger position at 40 ms (2 divisions to the right).
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Figure 35 is an example of the menu screen. Note the trigger points on the left and bottom of the screen.
Figure 35
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An example of the waveform from a properly functioning vehicle is provided in figure 36.
Figure 36
The CMP signal must be measured using red and black probe differential in this situation. Refer to the Advanced Application portion of this document for the reasons why and for more information.
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Monitoring CMP - O and CKP - O If the vehicle's concern is related to the CMP-O or CKP-O circuits, use the following information to view the signals.
To view these signals, the engine harness must be connected to the PCM. The 46 pin adapter with the 104 pin break out box is the preferred method of making connections to the necessary circuits.
The VMM must no longer be connected to an isolated battery. Restore the vehicle battery connections if a battery was previously isolated. Connect the VMM to a vehicle battery for its power source.
The FICM must be able to communicate with the PCM. Reinstall the FICM relay if previously removed. To prevent the engine from starting, disconnect the IPR or disconnect all 8 injectors. Disconnect the glow plug module to lessen the current draw.
Automatic configuration settings are available within the channel menus for CKP-O on channels 1 and 3 and for CMP-O on channels 2 and 4. In order to obtain a stable waveform, use the channel of CMP-O as the trigger source.
If it is necessary to view CMP also, use the method and settings described in the Monitoring CMP and CKP with PCM Connected section of the document to measure CMP as a differential input.
If it is necessary to view CKP with these signals, set the voltage scale to 200 mv/div, channel coupling to AC, and disconnect the CKP- circuit from the battery negative. These settings are the same as listed for channel 3 in the Monitoring CMP and CKP with PCM Connected section.
To connect the VMM channels 3 and 4 use the ignition transducer cables (C-404). Lead "A" of each cable is used with an adapter (T-017) to connect to the Break Out Box.
Refer to the following hookup illustration.
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6.0L Light Duty Hookup for Monitoring CMP-O and CKP-O
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The pattern relationship between CMP-O and CKP-O is similar to CMP and CKP. The CMP-O and CKP-O signals are essentially digital versions of the analog CMP and CKP signals. Therefore, any fault with the CMP or CKP inputs will likely be transferred into the CMP-O and CKP-O signals as well.
The CMP-O signal falls from high to low at the CMP falling edge 0 axis crossing point. See figure 37.
Figure 37
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In figure 38 the CMP-O signal was moved to allow easier viewing on the screen with the CKP-O signal added. Cursor A marks the CMP-O high-to-low transition and cursor B marks the CKP-O minus 2 teeth (or 2 pulse) area.
Figure 38
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The point of CMP falling edge 0 axis crossing and CMP-O high-to-low transition occur within the signal low portion of the 11th CKP-O pulse (counting from right to left from the minus 2 pulse area as with CKP pulses). Figure 39 contains labels to illustrate this.
Figure 39
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CKP, CKP-O, and CMP-O are shown together (overlaid) in figure 40. In this waveform, CMP-O was used as the trigger source.
Figure 40
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Advanced Application
In this section more detail will be explained regarding why the CMP and CKP signals appear as they do in this procedure.
The PCM uses the CKP sensor signal to monitor the crankshaft position and determine where the pistons are relative to top dead center for control of injection timing. Figure 45 shows that top dead center is indicated every 90 degrees of crankshaft rotation.
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Figure 45
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Review the engine firing order below.
Engine firing order 1-2-7-3-4-5-6-8
1st crankshaft revolution cylinders 1-2-7-3 will fire 2nd crankshaft revolution cylinders 4-5-6-8 will fire
Because of the 4 stroke cycle, there are always two cylinders reaching top dead center at the same time. The PCM can not determine which one is on the compression stroke and which one is on the exhaust stroke from the CKP signal alone. To determine which cylinder is approaching top dead center of the compression stroke, the PCM depends upon the camshaft position signal.
The CMP signal occurs once every second crankshaft revolution and allows the PCM to identify whether the crankshaft is on the first or second revolution in the firing order.
Visualize the crankshaft and camshaft rotating in the directions indicated in figure 45. The illustration indicates that the trigger peg in the camshaft will pass the CMP sensor before the minus 2 teeth area of the CKP trigger wheel passes the CKP sensor. Therefore, it can be expected that the oscilloscope waveform will show the CMP pulse before the CKP signal influenced by the 2 absent teeth.
A closer view of the mechanical relationship of the CMP and CKP components is provided in figure 46. With the trigger peg in the camshaft directly aligned with the CMP sensor (as it is in figure 45 and figure 46), count the number of CKP trigger wheel teeth between the minus 2 teeth area and the middle of the CKP sensor tip.
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Figure 46
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There are 11 teeth in the area described. Therefore it should be expected that the oscilloscope pattern will have 11 CKP pulses between the CMP signal and the CKP minus 2 teeth area.
Figure 47 is a waveform from a properly timed engine. This figure marks the beginning and ending of each CKP trigger wheel tooth pulse with a yellow line. The number in the center of each pulse corresponds to the number on the CKP trigger wheel in figure 46 and figure 48.
Figure 47
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The waveform in figure 47 displays the same relationship between the CMP and CKP electrical signals as the mechanical relationship of the physical parts illustrated in figure 45 and figure 46. One more topic bears discussing. The shape of each signal pulse has both a positive and a negative portion. Figure 48 is a display of only the CMP signal. Viewing from left to right, note the positive and negative portions. The signal initially rises positive, then falls and becomes negative, then rises back to 0. The point where the falling edge crosses the 0 axis is the point where the peg in the camshaft is directly aligned with the CMP sensor.
Figure 48
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Applying the same analysis to the CKP signal, review figure 49.
Figure 49
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Figure 49 illustrates that the CMP falling edge crosses the 0 axis within the negative portion of CKP tooth 11. The negative portion of the CKP pattern means that the trigger wheel tooth has passed the point of direct alignment with the CKP sensor. Note the inset illustration of the CKP trigger wheel and sensor showing the direction of rotation (tooth moving up).
In a properly timed engine, the CMP falling edge 0 axis crossing should fall within the negative portion of the 11th pulse (counted right-to-left) from the CKP minus 2 teeth area.
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CMP and CKP circuit bias voltage
To reduce the noise sensitivity on the CMP and CKP signals, the PCM applies a DC voltage to both CMP circuits and both CKP circuits. This processor supplied voltage offsets the signals above chassis ground. This makes the signals easier to distinguish from normal circuit noise.
The bias voltage of the CMP circuits is approximately 3.0 volts relative to battery negative.
The bias voltage of the CKP circuits is approximately 1.5 volts relative to battery negative.
Figure 50 shows these circuits at rest with the key on engine off while the PCM is connected.
Figure 50
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Figure 51 shows the raw CMP and CKP signals while cranking with the PCM connected and battery negative as the reference. In this configuration, it is much more difficult to clearly identify the exact point of the CMP falling edge 0 axis crossing.
Figure 51
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Because the CMP- and CKP- circuits are not connected directly to chassis ground, any measurement device which depends upon chassis ground as its reference will likely face difficulty in obtaining accurate measurements of the signals depending on the circuit conditions (frequency, other noise related to the vehicle's ground connections, etc.). This is especially true for the CMP signal which has a very low frequency while cranking (approx. 200 rpm of crankshaft while cranking = 100 rpm of camshaft 1 pulse per cam revolution = 100 pulses per minute 100 pulses per minute divided by 60 seconds per minute = between 1 and 2 Hz). Frequencies this low suffer from impedance and distortion if AC coupling is used.
The CKP signal frequency is high enough that it may be AC coupled during measurement.
These matters are avoided by leaving the engine harness disconnected from the PCM so that measurements are made without any bias voltage by manually supplying an isolated ground point shared with the VMM.
For cases where the PCM cannot be disconnected, differential measurement of the CMP sensor is required. Differential measurement means that the measurement device is connected to both the positive and negative signal circuits instead of only the positive circuit. Bias voltage is no longer a concern in differential mode because the measurement device now shares the same reference on the negative lead as the sensor signal return. Because the bias voltage is the same on the positive and negative circuits, it does not affect the measurement in differential mode.
The VMM is capable of measuring only one signal in differential mode. This method requires channel 1 and channel 2 working together on the positive and negative circuits of one sensor.
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6.0L F-650/750 Supplement The 96 pin Break Out Box with adapter for the engine sensor harness connector (C175c) allows access to the necessary circuits. Use the waveform examples of 6.0L light duty for diagnosis.
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4.5L Supplement For 2006-2007 LCF, the 96 pin Break Out Box with adapter for the engine sensor harness connector (C175c) allows access to the necessary circuits.
Hookup Diagram for Early LCF (2006-2007 MY)
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For 2008 and later MY LCF, use the VMM flex probes as shown.
Hookup Diagram for Late LCF (2008+ MY)
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Below is a sample waveform from a properly functioning 4.5L engine.
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For the 4.5L engine, the CMP falling edge 0 axis crossing will fall in the middle of the 21st CKP tooth to the left of the minus 2 teeth area. The following waveform was captured with the time base changed to 10 ms per div for clarity.
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Below is an example of the waveform when the time base was changed to 50 ms per division. Note how the CKP waveform amplitude becomes smaller as each individual cylinder goes through its compression stroke
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The following illustration shows how the CMP and CKP components relate to each other physically.
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6.4L Supplement A break out box is not currently available for this application. Flex probes may be used to make the connections as illustrated.
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Note: It is normal for the PCM to only allow the engine to crank briefly on each key cycle while the engine harness connector is disconnected.
Below is a waveform from a properly functioning 6.4L engine.
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Note that the CMP falling edge 0 axis crossing is similar to a 6.0L, but slightly more to the left within the 11th CKP tooth.
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Table of Acronyms and Terms Acronym/Term Definition AC Alternating Current AC Coupling Alternating Current Coupling – This term refers to how a signal is referenced by a measurement device. AC coupling references the signal via a capacitor. This blocks the DC component of the signal and effectively centers the waveform vertically on the oscilloscope screen. For example, AC Coupling is used when looking at alternator ripple. Bias Voltage Direct Current applied to a circuit to raise the signal above the noise threshold. BOB Break Out Box CMP Camshaft Position Sensor CKP Crankshaft Position Sensor CMP-O Camshaft Position Sensor Output signal (from PCM to FICM) CKP-O Crankshaft Position Sensor Output signal (from PCM to FICM) DC Direct Current DC Coupling Direct Current Coupling – This term refers to how a signal is referenced by a measurement device. DC coupling references the signal directly to ground. All DC and AC portions of the signal are visible. DC Offset Describes the appearance of a signal on the oscilloscope screen that has been moved vertically above or below where it would normally be, as if a Direct Current voltage were added or subtracted from the signal. ECM Engine Control Module FICM Fuel Injection Control Module IDM Injector Driver Module IDS Integrated Diagnostic System IPR Injection Pressure Regulator PCM Powertrain Control Module PID Parameter Identification Data
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TDC Top Dead Center VMM Vehicle Measurement Module
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