February_2022 - 28

Figure 2: Pressure pulses seen in the exhaust stream. Two of the six pulses are significantly lower, which indicates if an engine has a mechanical fault.
When the ECM de-energizes the solenoid control valve, the
supply oil is vented. Spring tension forces the hydraulic control
valve to close and the high-pressure oil in the master/slave cylinder
circuits is vented to the top of the hydraulic control valve. Normal
engine operation is restored.
WATCHING THE SYSTEM IN ACTION
So, how can we use tools to monitor this system? A better question
may be " Why would we want to? " Seeing a system in operation
will allow us to determine what " normal " looks like. And, as I
always say...
" If we know what 'Normal' looks like, 'Bad' sticks out like a
sore thumb. "
Using a capable lab scope and pressure transducer, in this case a
PicoScope and WPS500, we can not only see the changes in pressure
of the exhaust system but we can also correlate these changes
to specific cylinders. In plain English, it can help us determine why
the engine-brake system may not be functioning as it should and
which cylinder(s) are at fault.
With what was described above, we are now aware that the
compression pressure harnessed in the cylinder is then vented to
the exhaust stream. This event occurs just before the top of the
compression stroke. Meaning, a pressure spike should be visible
at this time, in the exhaust stream. All pressure spikes should be
visible from each engine-braking cylinder and they should all be
similar in amplitude (pressure-value).
Look at the capture (Figure 2). The channels are as follows:
* BLUE= CKP sensor signal
* GREEN=Exhaust system pressure pulses
28 PTEN FEBRUARY 2022 www.VehicleServicePros.com
This capture was taken during a deceleration event, in " high "
mode (all cylinders were commanded to provide engine braking).
Referencing service information, the firing order for this engine
was determined to be 1-5-3-6-2-4. In a known-good capture, it
was determined that the #1 fuel injector (fired near TDC of the
compression stroke) was occurring at four CKP pulses to the left
of the CKP sync pulse. On the screen is two full engine rotations
(one complete engine cycle) representing 720 degrees of crankshaft
rotation.
The waveform was partitioned equally in six ways to associate
the pulses with each of the six cylinders. As can be seen, two of
the six pulses are considerably low compared to the other four.
This lack of engine-braking contribution can likely be attributed
to low cylinder compression.
A relative compression test was performed and it was determined
that multiple cylinders had a loss of integrity but cylinders
5 and 3 were the worst offenders. The point is not that the vehicle
requires repair. It's not even the fact that we can see the variances in
the exhaust pressure waveform. The true point is that we can take
what we know from our past experiences and the results of the tests
we have grown to trust, and apply them to what we are trying to
now understand. I think we've proven that as a success in this case.
The shop was instructed to carry out the next step of a cylinder
pressure leakage test in cylinders 5 and 3. I don't have a conclusion
for you at this point as the truck is awaiting further testing
but again, that wasn't the point of this article.
Being familiar with the tools we choose to implement, taking
the time to educate ourselves on the systems we face and the
components of that system, we can capitalize and learn testing
http://www.VehicleServicePros.com

February_2022

Table of Contents for the Digital Edition of February_2022

NEW PRODUCTS
TOOL REVIEWS
CATEGORY SPOTLIGHT
EDITOR'S NOTE
DIAGNOSTIC TECH
TOOL BRIEFING
BIG TIME BOXES
February_2022 - 1
February_2022 - 2
February_2022 - 3
February_2022 - 4
February_2022 - 5
February_2022 - 6
February_2022 - 7
February_2022 - EDITOR'S NOTE
February_2022 - 9
February_2022 - NEW PRODUCTS
February_2022 - RSC1
February_2022 - RSC2
February_2022 - 11
February_2022 - 12
February_2022 - 13
February_2022 - 14
February_2022 - 15
February_2022 - 16
February_2022 - 17
February_2022 - 18
February_2022 - 19
February_2022 - 20
February_2022 - 21
February_2022 - 22
February_2022 - 23
February_2022 - 24
February_2022 - 25
February_2022 - DIAGNOSTIC TECH
February_2022 - 27
February_2022 - 28
February_2022 - 29
February_2022 - 30
February_2022 - 31
February_2022 - 32
February_2022 - 33
February_2022 - 34
February_2022 - 35
February_2022 - 36
February_2022 - 37
February_2022 - 38
February_2022 - 39
February_2022 - 40
February_2022 - 41
February_2022 - 42
February_2022 - 43
February_2022 - TOOL BRIEFING
February_2022 - 45
February_2022 - 46
February_2022 - 47
February_2022 - TOOL REVIEWS
February_2022 - 49
February_2022 - 50
February_2022 - 51
February_2022 - CATEGORY SPOTLIGHT
February_2022 - 53
February_2022 - 54
February_2022 - 55
February_2022 - 56
February_2022 - 57
February_2022 - BIG TIME BOXES
February_2022 - 59
February_2022 - 60
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https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/december-2022
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https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/september-2022
https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/august-2022
https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/july-2022
https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/june_2022
https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/2022scantoolspecguide
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https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/april_2022
https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/march-2022
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https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/december-2021
https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/october_2021
https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/september_2021
https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/pten_0821
https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/pten_0721
https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/scantoolspecguide2021
https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/pten_0621
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https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/may_2021
https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/professional_tool_and_equipment_news_april_2021
https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/pten_0321
https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/Professional_Tool_And_Equipment_News_February_2021
https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/Professional_Tool_And_Equipment_News_December_2020
https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/Professional_Tool_And_Equipment_News_October_2020
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https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/Professional_Tool_And_Equipment_News_August_2020
https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/Professional_Tool_And_Equipment_News_July_2020
https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/Professional_Tool_and_Equipment_News_June_2020
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https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/Professional_Tool_And_Equipment_News_February_2020
https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/Professional_Tool_And_Equipment_News_December_2019
https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/Professional_Tool_And_Equipment_News_Octoberr_2019
https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/Professional_Tool_And_Equipment_News_September_2019
https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/Professional_Tool_And_Equipment_News_August_2019
https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/Professional_Tool_And_Equipment_News_July_2019
https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/Professional_Tool_And_Equipment_News_June_2019
https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/Professional_Tool_And_Equipment_News_May_2019
https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/Professional_Tool_And_Equipment_News_April_2019
https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/PTEN_0319
https://www.nxtbook.com/endeavor/professionaltoolandequipmentnews/PTEN_0219
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