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2001 Ford Expedition 5.4L
This example starts us out with a 2001 Ford Expedition. It was misfiring badly an
it was determined that it needed new spark plugs and coil boots. After the installation
the misfire was gone but the vehicle still exhibited a mild lack of power. A test
drive and a few quick tests with
Escan
quickly hones in on the problem.
Our first test was for
Volumetric Efficiency.
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As you can see in the picture, the Actual airflow that was measured is lower than
the Calculated airflow, or the airflow that was expected from this engine. Either
this engine didn't breathe correctly or the Mass Airflow sensor incorrectly read
how much air was entering the engine.
We'll use these results with the results of our next test to formulate a conclusion
In this next test we will look at the
Fuel Trim Chart
gathered from the test drive. |
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As you can see in this
Fuel Trim Chart
at the lower RPM's on both banks the Long Term Fuel Trim or LTFT is -9 and-10, taking
away fuel. At the Higher RPM range you can see the the addition of fuel as noted
by a positive LTFT of 11 and 10. We can see that whatever is causing the difference
in trim of 20% is affecting both banks of the engine.
This trim pattern is indicative of a dirty Mass Airflow Sensor. We can confirm this
with the results of the
Volumetric Efficiency test
which showed at Wide Open Throttle that not enough air was being measured by the
MAF sensor. It was under reporting at higher RPM and over reporting at idle RPM.
The LTFT was compensating by changing the fuel calculation that was determined using
the dirty MAF sensor. |
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