Lean mixture fault

[Alex W]

My expedition keeps throwing a code that says that fuel bank 1 and 2 are lean. Autozone’s fix for this was the coils and plugs but after doing those, the fuel filter, fuel pump, and the o2 sensors the code will still come up after any kind of any kind of acceleration other than feathering the throttle. Does anyone have any idea what the problem could be? The only thing left I can think of is the injectors are going out. Thanks.

 

[highlandre]

I was getting lean codes due to header exhaust leaks. They were cracked and after I replaced them never had the issue again.

 

[Rich_007]

I was getting those codes on my 01 5.4.
Turned out to be EGR valve.
People on here told me that most common cause was vacuum leak. Which made sense that it was reading lean if unmetered air is getting in down stream of the sensor.
Lots of possibilities for that on an old engine, so I had the mechanic smoke check it, instead of just shotgunning all the possibilities.
Good Luck

 

[Rande Reynolds]

Try checking the vacuum hose off the vapor management, or vacuum hose behind throttle body. 90% of the time, a lean is a vacuum leak

 

[1955moose]

Richie's on the right track. Smoke the intake system. You'll be surprised where the smoke comes out of. It's the quickest way to get at your problem. Their may be other things, but start there.

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[uscgmac]

AutoZone has no clue. They use a basic scan tool which only shows the code. You need a code reader with live data. When your short term fuel trim is near zero and your long term fuel trims are 25% and higher it's usually a vacuum leak not a fuel delivery problem. The short terms will be high at first then go back to normal after the engine compensates for a while showing the long terms to be high. Usually when the long term goes above 25% then you throw a code. Check vacuum lines for anything obvious and then get a smoke test for the non obvious. I just had the same code and diagnosed a vacuum leak at the top of the PCV tube behind the throttle body.

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[Yupster Dog]

If you haven't already, check and clean the Mass Air Flow (MAF) sensor. That is something that is quick and easy to knock off the list of potential problems.

 

[Alex W]

Thank you guys. Turns out that my long terms are both above 25. Now to find the vacuum leak.

 

[rjdelp7]

Don't let auto parts store guys 'diagnose' problems. They are not experts. I would Google it first. Check your PCV vacuum hose. It is on the passenger side valve cover. It is common failure on this model.

 

[1955moose]

Read my #5 post again. You can buy a smoker as cheap as $35.00, or pay someone. It's quick, and your done with looking for the problem, just the fix.

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