My buddy has a 2002 Ford F150 4x4 with a 4.6 V8.For the last few months the truck has been running lean,and keeps tripping the service engine light.He keeps putting it in the shop,and they keep replacing parts and clearing the codes,but it's still doing the same thing.So far the Catalytic Converter has been replaced,the O2 sensors have been replaced,as well as 3 of the injectors on the passenger side.Yet it's still doing the same thing.What are all the possible causes that could be making the truck still run lean?Thanks in Advance.

 

Find out what the codes are and post them. could be something as simple as the rubber boot for the PCV tube on the back of the intake is shot.

 

Well with this kind of service called 'guessing', you might as well have taken it to a lawn mower shop for all the expense and results..
First, the codes most likely are being miss-interpeted.
A so called lean code does not always mean the motor is running that lean.
Reason: the lean code is the "FUEL TABLES" in the computer software are shifted as "rich" as they can go trying to correct for excess air passing through the cylinders.
This is the only way the condition can be reported.
If the shop were to look at live running engine data , at the fuel trim numbers, it would be seen imedediately that the trims are way off and is the clue to what is happening.
Likely issue is an air leak into the intake manifold that becomes "unaccounted for air" because it did not pass through the air meter for the computer to act on.
You paid for as expensive cat and other parts not related to the original fault, all due to guessing by a shop that does not know how things work or uses a scanner to see the operational data.
Find another shop that does or take a look at the hoses around the intake for being hard brittle and cracked allowing air to enter as unaccounted for. Look at the big hose between the air meter and the throttle body, the throttle body mounting and gasket.
Good luck.

 

Does he have a K&N filter, or another oiled filter?

With a K&N type filter, the oil from the filter coats the sensor wire in the MAF sensor usually resulting in a P0171 & P0174
Clean the MAF sensor, and see what happens.

 

Thanks for the replies y'all.

It's not my truck,so I don't have the codes off hand,but I can see if I can get them from my buddy.I personally wouldn't put the truck in a shop,because I know what the shops try and do,but my buddy has very limited automotive knowledge,so that's about the only thing he can do.He's gettin sick of payin their ridiculous bills,so that's why i'm tryin to figure out a source of the problem.I'll take a look and see if I can find any areas where air might be leaking and post what I find.Thanks again.