september2021 - 24

DIAGNOSTIC TECH
driveability, poor idle, etc. He explained
to us that he had just had the engine
rebuilt and it has never run right since.
We examined the vehicle's engine
performance and began performing
analysis and all along the way we documented
our findings (Figure 2).
After we acquired a running compression
test, we began to analyze the
data. One of the first observations
we made was that the actual spark
event was taking place at 5.4 degrees
BTDC and not at the 14-degrees
BTDC indicated by the timing light
and marks. The valve timing events
were measured and noted. Additionally,
the idle compression peaks were
observed at 110 psi, which is high but
assumed acceptable based upon the
engine performance modifications.
Based upon our findings, we recommended
installing the correct spark
plugs, set the ignition timing using the
in-cylinder pressure method, and fine
tune the air-fuel ratio across the engine
operating range.
The customer contacted us a few
months later to tell us that the vehicle
has been running fine and that the
fuel mileage went from 10 mpg to 14
mpg but was concerned that the engine
had low compression based upon our
data. We proceeded to explain to the
customer that a running compression
test is usually 60 to 65 percent of what
one would observe during a cranking
compression test (Figure 3).
Performing documentation like
this indeed can take additional time
but, in the end, it's well worth it.
The documentation is the story that
illustrates exactly what happened as a
vehicle entered the service center, what
was done, what wasn't done, and what
was recommended. Some shop management
systems make it very easy to
integrate their inspection items and
subsequently include additional rich
assets alongside descriptive text. Some
Figure 2 - Case study invoice documentation
Figure 3 - Running compression test (ignition timing check)
applications can be accessed by using
a smartphone or tablet which allows
a technician to use the voice-to-text
feature instead of typing out a long
story. Initially this may take a little bit
of practice but once you get this down,
it becomes easy to handle. Many scan
tools and diagnostic equipment on the
market today are web connected which
can be a good thing, especially if the
device has a web browser and your
shop is using a shop management
24 Professional Distributor I September 2021 I VehicleServicePros.com
system that can be accessed through
the web.
MODERN TOOLS
During every maintenance service
at my shop, we perform a vehicle
health-check scan of all modules for
diagnostic trouble codes (DTCs). We
take that report and digitally attach it
to the repair order. Most of our scan
tools today are PC/tablet based and
have web access which allows us to

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september2021

Table of Contents for the Digital Edition of september2021

Editor's Note
Sneak Peek
Most Wanted
in Focus
In a flash
Diagnostic Tech
Show Me Your Truck
Go Sell Something
Driving Sales
Tales from the Road
september2021 - 1
september2021 - 2
september2021 - 3
september2021 - Editor's Note
september2021 - 5
september2021 - Sneak Peek
september2021 - 7
september2021 - 8
september2021 - 9
september2021 - 10
september2021 - 11
september2021 - Most Wanted
september2021 - 13
september2021 - in Focus
september2021 - 15
september2021 - 16
september2021 - 17
september2021 - In a flash
september2021 - 19
september2021 - 20
september2021 - 21
september2021 - Diagnostic Tech
september2021 - 23
september2021 - 24
september2021 - 25
september2021 - Show Me Your Truck
september2021 - 27
september2021 - Go Sell Something
september2021 - 29
september2021 - Driving Sales
september2021 - 31
september2021 - 32
september2021 - 33
september2021 - Tales from the Road
september2021 - 35
september2021 - 36
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