December 2023 - 19

After our attempt, we took the vehicle back out on the road
for a repeat test and Figure 9 shows our results.
As you can see, the numbers have greatly improved. The
absolute load is now at 77.2 percent which aligns with our
quick math on the cylinder air equation. We sold a new MAF
sensor, cleared all adaptive memory, and placed the vehicle
back into service where it is currently operating properly. What
we learned here is that although you may have a gross error
(multiple defective coils), a diagnostic technician should always
remain curious and perform a final road test evaluation while
recording the proper key performance indicators. Now if we
had good airflow numbers with a lean exhaust, then we would
proceed to investigate the fuel supply side of the vehicle.
Looking back on my two images (Figures 8 & 9) you can see
the 3-dimensional graph in the lower right of the screen. This
graph is configured to show an averaged value of long-term
fuel trim (LTFT) over an RPM/cylinder airmass table. Some
scan tools allow you to configure tables like this which can be
useful for visualizing data. In fact, looking back on Figure 2,
this table was used to monitor boost on a turbocharged vehicle
that was suspected of having an intermittent leaking wastegate
valve. This chart takes advantage of a math PID that automatically
finds the difference between actual and desired boost.
CONCLUSION
Modern driveability diagnosticians not only rely heavily on
scan tools and OBD-II data to troubleshoot performance
issues effectively, but they must also possess the inquisitiveness
necessary to properly analyze and diagnose these systems.
They also need to have a heightened level of situational
awareness of the tools and equipment available to take on
these demanding tasks.
SCOTT BROWN is an ASE Master Certified L1
Technician and has over 37 years of professional
service industry experience. He is an independent
shop owner in Southern California and is engaged
at various levels within the industry. He has a deep
understanding of the challenges technicians experience at the service
level and is continuously striving to move the industry forward
through education and networking. Brown founded Diagnostic
Network (diag.net) after 22 years of service at iATN, where he retired
as company president in 2018.
SBrown@VehicleServicePros.com
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December 2023

Table of Contents for the Digital Edition of December 2023
