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What causes lean codes?

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Old 10-10-2006, 04:35 PM   #1
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Default What causes lean codes?

First off,I cleared the codes after I read them.But, it read lean bank one and pending lean bank two.My wife filled the tank of our 1999 5.3 f150,and then she drove an eighty mile loop to/from out of county shopping.The chk eng light came on just short of getting home.Our truck also cranks for ten seconds when first started each day,then it fires in three to four seconds thereafter unless it sits for many hours.Last month I had a cyl#6 misfire code that was a bad coil.I could feel the miss long before the computer set the code.The truck used to take two to three seconds to start as recently as four years ago.With this info, do you think my fuel pump is degrading (has new filter),or did we just get some water in our gasoline?We have driven about fifty miles and the chk eng light has not come on again.Also,if I prime the injectors by cycling the ign switch a few times, it still takes ten seconds at first,but then leaves a black cloud too.I know that a lean code is set when there is too much oxygen in the exhaust, and that the computer cannot know lean from a minor missfire, so what are the truck's possible problems?
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Old 10-11-2006, 02:48 PM   #2
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I'll be honest with you edman, it's a little over my mechanical expertise.
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Old 12-02-2006, 08:59 AM   #3
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I have a '97 Ford F150 that had a problem with the "lean" code... It would backfire when the motor was in low RPMs and when switchin' from first to second gear. Truck ran horrible so, I took it to my brother who is a mechanic and neither him nor his buddy could figure out what was wrong. Well, atleast in my case it is fairly simple. The problem I had was in the air intake... On the O2 senser the connector is located roughly two to three inches inside of its bulky housing (which I had no clue of). Well, the wires running to the sensor has a rubber stopper that fits in the hole on the outside of the housing. I thought it fit around the connector and the plug was right inside the hole. The next day or so, I noticed the sensor was unplugged so I decided to examine the housing a little better and that's when I realized the O2 sensor was never plugged in. So in short do what I did, examine the housing on the O2 sensor and make sure the connection didn't come out or loose. The plug should be on the bottom of the housing.
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Old 12-26-2006, 04:58 PM   #4
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Lean Codes Tend to mean a vacuum leak somewhere unless you have have a bad front O2 sensor either one could cause the vehicle to start up slowly though. Only thing you can do is test the voltage on the O2 sensor or just check for vacuum leaks.
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Old 12-27-2006, 01:03 PM   #5
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Quote:
Originally Posted by streethoboz View Post
I have a '97 Ford F150 that had a problem with the "lean" code... It would backfire when the motor was in low RPMs and when switchin' from first to second gear. Truck ran horrible so, I took it to my brother who is a mechanic and neither him nor his buddy could figure out what was wrong. Well, atleast in my case it is fairly simple. The problem I had was in the air intake... On the O2 senser the connector is located roughly two to three inches inside of its bulky housing (which I had no clue of). Well, the wires running to the sensor has a rubber stopper that fits in the hole on the outside of the housing. I thought it fit around the connector and the plug was right inside the hole. The next day or so, I noticed the sensor was unplugged so I decided to examine the housing a little better and that's when I realized the O2 sensor was never plugged in. So in short do what I did, examine the housing on the O2 sensor and make sure the connection didn't come out or loose. The plug should be on the bottom of the housing.
thats not a o2 sensor, its our mass air flow sensor.

i woud check that, or your o2 sensors. or take it to a ford stealership and have them look at it.
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Old 12-27-2006, 02:09 PM   #6
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That is a possiblity, but unless you have access to a Diagnostic tool (scanner) and the parameters that the mass air flow is supposed to be within your not gonna get far with checking that lol
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Old 09-16-2007, 11:32 AM   #7
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sometimes lean codes can be caused by low fuel pressure....if you have dual tanks on your truck check fuel pressure in both tanks.......

if engine light comes on switch to rear tank ,unplug the neg battery cable for few minutes to reset computer run the truck for a few days if light remains off then u got a bad fuel pump in front tank..try it in reverse if liight comes on u know it is the pump..


if not check make sure u dotn have bad plug wires or a bad plug....best way to check the wires is at night...a damp night preferably...if u see sparks under the hood when engine is running hehe u got badwires....

other than that i am not sure of what else would cause it...
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Old 09-16-2007, 06:48 PM   #8
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Bad wires or plugs cannot cause it to run lean. That will cause a rich condition because the fuel is not being burned. Check for a vacuum leak. Check the EGR valve. Make sure the 02 sensors are doing their job.
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Old 09-16-2007, 06:54 PM   #9
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and clean the MAF wires.
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Old 09-16-2007, 08:54 PM   #10
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Quote:
Originally Posted by Ty View Post
thats not a o2 sensor, its our mass air flow sensor.

i woud check that, or your o2 sensors. or take it to a ford stealership and have them look at it.
thank you................lol............
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