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Select VEHICLE & ENGINE SELECTION menu.
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Select NEW VEHICLE, YEAR & MODEL.
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Follow operating manuals from scan tool menu.
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Select GENERIC OBD-II FUNCTIONS. Press CONT button if OBD-II monitors are not complete.
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Turn ignition switch to ON position.
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Select FREEZE FRAME PID TESTS.
DIAGNOSING ADAPTIVE FUEL DTCS
Description
Adaptive fuel DTCs diagnostic techniques help isolate root causes of adaptive fuel concerns. Before
proceeding, road test vehicle to verify if any driveability concerns are present. These diagnostic aids are meant
as a supplement to system test steps under SYSTEM TESTS. For a description of fuel trim, see FUEL TRIM
under POWERTRAIN CONTROL MODULE SOFTWARE under COMPUTERIZED ENGINE CONTROLS
in THEORY & OPERATION - CNG, FLEX-FUEL & GASOLINE article.
Obtain Freeze Frame Data
Freeze Frame Data can be helpful in duplicating and diagnosing adaptive fuel concerns. This data (a snapshot of
certain PID values, recorded at time DTC was stored in Continuous Memory) is helpful to determine how
vehicle was being driven when fault occurred, and can be especially useful on intermittent concerns. Freeze
Frame Data, in many cases, can help to isolate possible areas of concern as well as rule out others. See
FREEZE FRAME DATA MODE for a more detailed description of this data.
Using LONGFT1 & LONGFT2 (Dual Bank Engines) PIDs
LONGFT1 or LONGFT2 PIDs can be useful for diagnosing fuel trim concerns. A negative PID value indicates
that fuel is being reduced to compensate for a rich condition, while a positive PID value indicates that fuel is
being increased to compensate for a lean condition. It is important to know that there is a separate LONGFT
value that is used for each RPM/load point of engine operation. When viewing LONGFT1 or LONGFT2 PIDs,
values may change a great deal as engine is operated at different RPM and load points. This is because fuel
system may have learned corrections for fuel delivery concerns that can change as a function of engine RPM
and load. LONGFT1 or LONGFT2 PIDs will display fuel trim currently being used at that RPM and load point.
Observing these changes in LONGFT1 or LONGFT2 PIDS can help when diagnosing fuel system concerns.
For example:
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A contaminated MAF sensor would result in matching LONGFT1 and LONGFT2 correction values that
are negative at idle (reducing fuel), but positive (adding fuel) at higher RPM and loads.
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LONGFT1 values that differ greatly from LONGFT2 values would rule out concerns that are common for
both banks (for example, fuel pressure concerns, MAF sensor, etc. could be ruled out).
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Vacuum leaks would result in large rich corrections (positive LONGFT1 and LONGFT2 value) at idle,
but little or no correction at higher RPM and loads.
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A plugged fuel filter will result in no correction at idle, but large rich corrections (positive LONGFT1 or
LONGFT2 value) at high RPM and load.
2003 Ford Pickup F150
2003 ENGINE PERFORMANCE Self-Diagnostics - CNG, Flex-Fuel & Gasoline