February_2022 - 26

Advanced diagnostics:
a diesel engine mechanical fault
Use a capable lab scope and pressure
transducer to see the changes in pressure of
the exhaust system.
By Brandon Steckler, Technical Editor
N
ot a heavy duty diesel tech? That's fine; neither
am I. But one tried-and-true method of
acquiring new knowledge is to implement the
tools we've learned to trust and invest some time
in some research. This combination has served me
well in developing hypotheses and proving them out
through experimentation.
THE TASK AT HAND
The subject of the day, a huge Caterpillar 14.7L 3406e diesel engine
situated in a Kenworth W900 dump truck. The truck comes to us
with the complaint from the operator that the powerplant's compression
brake doesn't seem to slow the vehicle as it has in the past.
With a little research and input from my brilliant HD tech friend
and instructor, Brent Delfel of Advanced Diagnostic Consulting,
I'd like to show you what I have learned from him.
The compression-brake system assists in slowing the tremendous
vehicle in two ways. First, utilizes the compression stroke of
the large diesel engine to slow the crankshaft down. At the top of
the compression stroke, the highly pressurized cylinder charge
is then " wasted " . Just at the point when combustion of the diesel
fuel would normally occur, the delivery of the fuel is canceled and
the exhaust valve is momentarily allowed to open. As a result,
compression is shed on the exhaust stream.
A moment later, the exhaust valves are allowed to close, sealing
the cylinder once again. The piston will continue to descend on
what would normally be a power stroke. Instead, as it's descending
a negative pressure (or " vacuum " ) is created in the cylinder,
on top of the piston. This vacuum in the combustion chamber is
what also assists in slowing the crankshaft down. Engine-braking
occurs when there is no accelerator input and the clutch engages
the engine and the transmission. As long as the engine is mechanically
connected to the transmission and road wheels, the vehicle
will slow as well. This is why it's called an " engine brake. "
There are three levels of engine braking (low/medium/high). In
low, only two cylinders have engine-braking capability (cylinders
26 PTEN FEBRUARY 2022 www.VehicleServicePros.com
Mechanical
Electric
Unit
Injector
Injector
Rocker/
Injector
Exhaust
Rocker/
Valve
Master
Cylinder
Pushrod
Location
Input
from
Slave
Cylinder
Intensifier
Piston
Figure 1: The camshaft-driven rocker arms (top) for a single cylinder.
The center rocker arm operates the MEUI injector (bottom).

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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