Ford Focus Runs lean, P0191, P0171 Errors

2005 Ford Focus Problem

CarFord Focus 2.0L
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The problem occurs after I've driven continuously for 100-120 miles. The symptoms indicate the motor is not getting enough gasoline. I can stop the vehicle for a couple minutes and start the motor and continue on my way without any problems until I drive another 60-80 miles and the problem re-occurs. I have changed the fuel filter and checked for vacuum leaks. I can clear the error codes, but they re-occur when the problem re-appears. Local driving does not show the problem. Thank you
Problem Category
Electrics, ECU, Warnings & Lights

Running Rough, Starting & Power Loss

Solution 1
whittingehame | Legend | Since: Oct 2009 | Posts: 444 | Fixes: 11829 | View Garage
Suggested Solution

P0171 - System to Lean (Bank 1) The Adaptive Fuel Strategy continuously monitors fuel delivery hardware. The test fails when the adaptive fuel tables reach a rich calibrated limit. For lean and rich DTCs:
Fuel system
Excessive fuel pressure.
Leaking/contaminated fuel injectors.
Leaking fuel pressure regulator.
Low fuel pressure or running out of fuel.
Vapor recovery system.
Induction system:
Air leaks after the MAF.
Vacuum Leaks.
PCV system.
Improperly seated engine oil dipstick.
EGR system:
Leaking gasket.
Stuck EGR valve.
Leaking diaphragm or EVR.
Base Engine:
Oil overfill.
Cam timing.
Cylinder compression.
Exhaust leaks before or near the HO2Ss.
A SHRTFT-1,2 PID value between -25% to +35% and a LONGFT-1,2 PID value between -35% to +35% is acceptable. Reading beyond these values indicate a failure.

P0191 - Fuel Rail Pressure Sensor Circuit Performance (FRP) The comprehensive component monitor (CCM) monitors the FRP pressure for acceptable fuel pressure. The test fails when the fuel pressure falls below or exceeds a minimum/maximum calibrated value for a calibrated period of time. High fuel pressure.
Low fuel pressure.
Damaged FRP sensor.
Excessive resistance in circuit.
Low or no fuel.
A FRP PID value during KOER of 138 kpa (20 psi) and 413 kpa (60 psi) for gasoline or 586 kpa (85 psi) and 725 kpa (105 psi) for natural gas vehicles (NG) is acceptable.

Posted on Thursday 9th of July 2015
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Solution 2
1/4drive | Auto Insider | Since: Jun 2011 | Posts: 25 | Fixes: 1847 | View Garage
Suggested Solution

Both of your codes indicate to me fuel pump/supply problems.
And a regular fuel pressure test might be inconclusive.
So what I would do for a test would be a pattern waveform on the oscilloscope,
I'd say no other test would show up where the fault is.

Posted on Friday 10th of July 2015
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