December 2021 - 73

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Bosch
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Launch Tech USA
X-431 Turbo
dicting cylinder air during engine operation
for most manufacturers. However,
there are some today using other methods
such as neural networks to build artificial
intelligence with great success.
FUEL TRIM DIAGNOSTICS
Fuel trim is a key indicator of how well the
overall engine performance and fuel delivery
systems are performing. For service
technicians, it can provide an invaluable
path towards a resolution. As mentioned
earlier, it usually takes a wild swing in fuel
trim to flag a fault and therefore fuel trim
can be used to identify trouble before it
flips on the malfunction indicator lamp
(MIL). It's always a good practice to monitor
fuel trim along with a few other parameters
when assessing engine performance
issues. Knowing what can drive fuel trim
numbers can help technicians arrive at
the right hypothesis and therefore issue
the proper repairs that generate success.
Looking at Figure 1, you can see in the
lower graph that >20 percent fuel is being
removed via long-term fuel trim (LTFT)
on both banks. This vehicle is a flex fuel
vehicle and the revealing factor here is that
while the engine control module (ECM)
was targeting EQ or Lambda 1, the commanded
air-to-fuel ratio at 11.63:1. This
means that the ECM had inferred the
composition of the fuel to have roughly
52 percent ethanol. The other anomaly
here is that the mass air flow signal is over
reporting air flow.
Monitoring and recording engine performance
parameters can produce great reference
material for diagnosticians. Having a
deeper understanding of the inner workings
of the ECM and its various strategies
will no-doubt bear success when dealing
with engine performance and emissions
related challenges.
SCOTT BROWN is an ASE
Master Certified L1 Technician
and has over 37 years of
professional service industry
experience. He is the founder
of the Diagnostic Network.
sbrown@vehicleservicepros.com
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December 2021

Table of Contents for the Digital Edition of December 2021