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The code P0171 is a lean code, if you sure both lower and upper intakes are sealing and you have no other leaks. I would suspect eaither a bad HO2S (bank 1) or a fuel pressure issue.
Long and Short Term Fuel Trim Short Term fuel trim is a PCM parameter identification (PID) used to indicate Short Term fuel adjustments. This parameter is expressed as a percentage and its range of authority is from -10% to +10%. Once the engine enters closed loop, if the PCM receives a HO2S signal that indicates the A/F mixture is richer than desired, it moves the SHRTFT command into a more negative range to correct for the rich condition.If the PCM detects the SHRTFT is adjusting for a rich condition for too long a time, the PCM will "learn" this fact, and move LONGFT into a negative range to compensate so that SHRTFT can return to a value close to 0%. Once a change occurs to LONGFT or SHRTFT, the PCM adds a correction factor to the injector pulsewidth calculation to adjust for any variations. If the change is too large, the PCM will detect a fault.
Note: If a fuel injector or fuel pressure regulator is replaced, do a PCM Reset and then drive the vehicle through the Fuel System Monitor drive pattern to reset the Fuel Control table in the PCM.
Help for Fuel Trim Trouble Codes (P0171, P0172, P0174 & P0175) The Fuel Trim readings on a Scan Tool do not always indicate a problem by themselves. However, Fuel Trim readings can be a real asset when attempting to determine the cause of one of these trouble codes, and to determine "where to start testing" to find the cause of an Air/Fuel mixture problem or Fuel System control related fault (i.e., related to a fuel control sensor or solenoid that may have failed).One of the first steps is to determine if the PCM is in "control" of the fuel delivery system. There are many different methods that can be used to make this determination. If the PCM is not in "control" of the fuel delivery system, the repair table below can help find the problem.
Fuel Trim Repair Table
|HO2S Signal||Tailpipe Emissions||Fuel Trim Value||Logical First Step|
|Rich (high O2S voltage)||Rich A/F Mixture||PCM adding fuel||(+%)||Check PCM power and ground circuits for faults|
|Rich (high O2S voltage)||Rich A/F Mixture||PCM subtracting fuel||(-%)||High fuel pressure, leaking injector(s), intake is restricted, plugged exhaust (MAP sensor)|
|Rich (high O2S voltage)||Lean A/F Mixture||PCM adding fuel||(+%)||Irrational result - more than 1 fault is present!|
|Rich (high O2S voltage)||Lean A/F Mixture||PCM subtracting fuel||(-%)||HO2S is contaminated, or the HO2S Heater power circuit is shorted to the HO2S signal|
|Lean (low O2S voltage)||Rich A/F Mixture||PCM adding fuel||(+%)||Exhaust leaks in the manifold or pipes, air injection leaks in front of the HO2S or the HO2S is contaminated or has failed|
|Lean (low O2S voltage)||Rich A/F Mixture||PCM adding fuel (+%)||Irrational result - more than 1 fault is present!|
|Lean (Low O2S voltage)||Lean A/F Mixture||PCM subtracting fuel (-%)||Low fuel pressure, clogged fuel injectors, large vacuum leak, MAF sensor is contaminated|
|Lean (Low O2S voltage)||Lean A/F Mixture||PCM subtracting fuel||(-%)||Check PCM power and ground circuits for faults|
|Lean or Rich (low or high O2S volts)||Lean or Rich A/F Mixture||0% Short Term Fuel Trim reading||Engine operating in Open Loop mode or Limp-In mode - check for any stored trouble codes|
MIL Operation, How to Clear Memory Codes This Monitor is a two-trip monitor that runs continuously whenever the engine is running in closed loop. The first time the PCM detects a Fuel Trim fault; the PCM sets a "pending" code and records the current vehicle conditions in Freeze Frame. If the same fault is detected on consecutive trips, the PCM turns on the MIL and sets a diagnostic trouble code.This OBD II Monitor uses a unique set of rules to turn off the MIL. The engine must be running with the engine speed and load in a similar range to when the trouble code first set before the PCM will retest the same fault. If this Monitor passes for (3) consecutive trips, the MIL is turned off. If it passes for 40 warmup cycles under "similar conditions", the PCM will clear the code. If the engine does not run under these "similar conditions", the code will be cleared after 80 warmup cycles if the same fault does not reappear.Fuel System Monitor Repair Verification An example of how to drive a vehicle to verify the repair of a trouble code related to the Fuel System Monitor on this vehicle application is shown in the Graphic below.