This is a Ford Expedition 5.4 with a vacuum leak causing "System Too Lean" trouble codes P0171 and P0174. In this video I will show you how to use freeze frame data and fuel trim numbers to identify a vacuum leak. Then I will be using water to locate the specific area of the vacuum leak.

Engine Performance Diagnostics chapter 1 pages 9-12


  • rough idle
  • poor gas milage
  • check engine light (P0171, P0174)
  • hesitation
  • misfire
  • runs better with engine warm

fix 50

  • replace leaking intake manifold gasket

test shown

  • how to use freeze frame data to identify the type of lean condition
  • how to read and interpret STFT and LTFT numbers
  • how to locate a vacuum leak with water
  • how to locate a vacuum leak with a smoke machine

Tools used

  • global OBD-II scan tool
  • water bottle

end faq

{accordionfaq faqid=accordion15 faqclass="dotluvfaq help2 aligncenter headerbackground headerborder contentbackground contentborder round7" active=item0}


(Chapter 1) Misfire ID, Compression Tests, Vacuum Leaks, Fuel Trim, Head Gasket, Restricted Exhaust, Low Power, DMM

Related videos:

Understanding Short Term and Long Term Fuel Trim (an SD Premium video):


Causes of lean condition trouble codes P0171, P0174 - GM 5 3L:


P0507 Idle Speed Performance Higher Than Expected (vacuum leak) - Jeep:


Ford F-150 P0171 P0174 Trouble Codes - vacuum leak (water test):


How to find a vacuum leak with water:


end faq

{accordionfaq faqid=accordion3 faqclass="darkhivefaq defaulticon headerbackground headerborder contentbackground contentborder round5" active=item0}

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.

Want even more diagnostic training? Whether you are a DIY trying to fix your own car, someone looking to become an auto technician, or a current auto technician that wants to get more into diagnostics, subscribe to ScannerDanner Premium. There is a 14 day free trial.

On ScannerDanner Premium I will bring you right into my classroom at Rosedale Technical College. You will find page for page lectures taken right from my book as well as exclusive classroom type case studies. What is so special about these classroom case studies? I pull live problem vehicles directly into my classroom and we troubleshoot them in real time, using and applying the theory and testing procedures we learn during the classroom lectures. There is no better on-line training of how to troubleshoot automotive electrical and electronics systems anywhere!