1999 Mercury Mountaineer 5.0 with a P0171 and P0174 DTC in memory. This is a great video on using fuel trim and freeze frame data to determine the cause of the lean condition.

Engine Performance Diagnostics chapter 4 pages 12-19

symptoms 50

  • low power
  • lean exhaust trouble codes P0171 and P0174
  • pinging
  • hesitation
  • surging

fix 50

  • replace fuel pump and fuel filter

test shown enh 50

  • how to determine MAF sensor condition using BARO HZ data
  • how to use freeze frame data to determine type of lean condition
  • how to use STFT and LTFT at different loads to determine type of lean condition
  • how to test fuel pressure with a gauge
  • how to determine fuel delivery design
  • how to measure fuel pump current with a scope
  • how to locate the fuel pump inertia switch
  • how to calculate fuel pump RPM

Tools used

  • scan tool
  • fuel pressure gauge
  • Picoscope
  • inductive low amp probe

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(Chapters 14, 15,16) Fuel Delivery and Fuel Pressure Testing

Related videos:

Low Fuel Pressure from a bad fuel pump ground (Ford Ranger):


Symptoms and Causes of Low Fuel Pressure (Part 1):


Symptoms and Causes of Low Fuel Pressure Part II (new fuel pump) :


How to test an electric fuel pump (1997 4.3L Chevy Blazer CPI):


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For more information on this topic, I have written a “field manual” called Engine Performance Diagnostics which is available as an eBook or paper book.

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