2003 Ford Explorer Sport Trac

Tiny
CISCO
  • MEMBER
  • 2003 FORD EXPLORER
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 69,234 MILES
I HAVE A ENGINE CHECK LIGHT ON, SO I PUT IN MY OBD2 DIAAGNOSTIC AND IT READED PO174 (FUEL SYSTEM TOO LEAN CLYLINDER BANK 2
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Sunday, April 24th, 2011 AT 11:44 PM

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Tiny
BMRFIXIT
  • EXPERT
Vacuum leaks is most likely
Check hoses and check PCV valve hose
Smoke test would be best to locate the leak

P0171/P0174 System Too Lean Diagnostic Aids
NOTE:If the system is lean at certain conditions, then the LONGFT PID would be a positive value at those conditions, indicating that increased fuel is needed.

The ability to identify the type of lean condition causing the concern is crucial to a correct diagnosis.
Air Measurement System
With this condition, the engine will run rich or lean of stoichiometry (14.7:1 air/fuel ratio) if the PCM is not able to compensate enough to correct for the condition. One possibility is that the mass of air entering the engine is actually greater than what the MAF sensor is indicating to the PCM. For example, with a contaminated MAF sensor, the engine will run lean at higher RPM because the PCM will deliver fuel for less air than is actually entering the engine.
Examples: MAF sensor measurement is inaccurate due to a corroded connector, contaminated or dirty connector. A contaminated MAF sensor will typically result in a rich system at low airflows (PCM will reduce fuel) and a lean system at high airflows (PCM will increase fuel).
Vacuum Leaks/Unmetered Air
With this condition, the engine will run lean of stoichiometry (14.7:1 air/fuel ratio) if the PCM is not able to compensate enough to correct for the condition. This condition is caused by unmetered air entering the engine, or due to a MAF malfunction. In this situation, the volume of air entering the engine is actually greater than what the MAF sensor is indicating to the PCM. Vacuum leaks will normally be most apparent when high manifold vacuum is present (for example, during idle or light throttle). If freeze frame data indicates that the concern occurred at idle, a check for vacuum leaks/unmetered air is the best starting point.
Examples: Loose, leaking, or disconnected vacuum lines, intake manifold gaskets, or O-rings, throttle body gaskets, brake booster, air inlet tube, stuck/frozen/aftermarket PCV valve, unseated engine oil dipstick.
Insufficient Fueling
With this condition, the engine will run lean of stoichiometry (14.7:1 air/fuel ratio) if the PCM is not able to compensate enough to correct for the condition. This condition is caused by a fuel delivery system concern that restricts or limits the amount of fuel being delivered to the engine. This condition will normally be apparent as the engine is under a heavy load and at high RPM, when a higher volume of fuel is required. If the freeze frame data indicates that the concern occurs under a heavy load and at higher RPM, a check of the fuel delivery system (checking fuel pressure with engine under a load) is the best starting point.
Examples: low fuel pressure (fuel pump, fuel filter, fuel leaks, restricted fuel supply lines), fuel injector concerns.
Exhaust System Leaks
In this type of condition, the engine will run rich of stoichiometry (14.7:1 air/fuel ratio) because the fuel control system is adding fuel to compensate for a perceived (not actual) lean condition. This condition is caused by oxygen (air) entering the exhaust system from an external source. The HO2S will react to this exhaust leak by increasing fuel delivery. This condition will cause the exhaust gas mixture from the cylinder to be rich.
Examples: Exhaust system leaks upstream or near the HO2S, cracked/leaking HO2S boss, malfunctioning secondary air injection system.
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Monday, April 25th, 2011 AT 12:14 AM

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