well i got a 01 f 150 4.2 v6 well the other month bank 2 lean well i waited till i got the money to get a o2 sensor, well then it should both bad ok so i bought both and replaced them took out the factory ones cleared code and ran fine for a day then its back on lean on bank 2, cleared it again ran one day came back on again same code. what else can it be ? i know i heard some one say here the intake leaking? any way to know for sure thats it? i have not got by the dealer to find out how much it would cost to replace the gaskets on the intake.

 

4.2--does that have a plastic intake manifold? Could be cracked. You can use WD40 or other spray to locate the crack. Spray carefully at idle, see if the idle changes.

 

Anything that puts extra air into your intake on just one side can cause that. Defective gaskets between the 2 halves of your intake manifold plenum can do that. So can defective isolator bolts which hold the bottom half of the plenumb down to the metal intake manifold. Ford recommends that whenever you open up the intake manifold plenum, you replace both the gaskets and the isolator bolts.

 

well i will call the dealer tomorrow and see what the price will be to replace the bolts and gaskets on the intake.

 

You might be shocked, but I hope not. I talked to a good local shop about cleaning the EGR ports in my intake manifold (which entails replacing those bolts & gaskets (time consuming), and scraping the crud out of the ports (easy as dirt) - they quoted me $400, mostly for the labor.
After a year of off & on internet research, I learned how to do it myself, paid about $50 for new gaskets and isolator bolts from Rock Auto & carb cleaning spray from Wally World, this all worked like a charm & no more EGR error codes for 7 weeks now. While doing all that I discovered my real problem was a clogged EGR valve which only cost $50, and was much simpler to service than that plenum was. If I had removed the EGR first and closely examined it, I wouldn't have had to pay for the gaskets & bolts at all - but you should replace them whenever you take the intake manifold plenum apart - at least that's what Ford recommends. Your description of your situation sounds like you will have to open up your plenum.
Another problem in older 4.2L V-6's are the plastic bushings for the IMRC valve system -- they tend to fail abruptly & will give their own unique CEL code. Unless you remove the intake plenum, they are about impossible to get to. Some recommend replacing the IMRC bushings whenever you service the intake plenum, since you can at least get to the bushings then. Bushings are dirt cheap, labor to get to them very expensive. See here for more info: https://sites.google.com/site/fordf1...rc-bushing-fix
I bought my bushings before I attacked my intake manifold plenum but when I saw what I would have had to do to replace the bushings, I decided to leave well enough alone - my old bushings are working.
Be sure to inspect every vacuum line & connectors attached to your intake manifold - if these are leaking, they can be fixed with less difficulty & expense than opening up the manifold plenum will cost you.

 

what code is coming up im having a similar problem, if you have to do the intake plenum gaskets there not hard i did mine in about and an hour and a half, the gaskets and bolts from ford are outragously priced i got the isolator bolts from ford and gaskets from autozone

 

It's more than one code - any code showing lean conditions originating in the intake manifold could be due to the bad isolator bolts or leaking gaskets. Two codes I have read about were P1131 and P1151, but there are others. The isolator bolts are permanently mounted inside special rubber holders - if these holders get too stiff or if they crack, they won't seal properly & will allow unmetered air into the intake manifold. You have to unscrew the isolator bolts to separate the lower half of the intake plenum off of the metal manifold underneath, but then you have to tap each isolator bolt assembly backwards out of its socket in the in the plenum to get the whole thing to pop out. Screwing in new isolator bolts is easier, the bolt draws the rubber part down and pops it into a semi-permanent position. After that the rubber part seals the area around the bolt to prevent air intrusion. Easier to see than to describe.