2001 explorer sport trac system lean bank 1 and misfire cyl 1
 

My 01 sport trac has the 4.0 v6 sohc. when I start the truck I get the CEL on. I pulled the code and it says system too lean bank 1... Then when the truck heats up to normal temp it idles and runs very rough.. I also get the flashing CEL which is misfire cyl 1... I tried pulling cylinder 1 plug and it looked ok... I replaced it with a new plug and the truck ran fine for about 10 mins then back to the same thing again... system lean bank 1 and misfire cyl 1.... does anyone have any ideas....

It sounds like you either have a vacuum leak or a fuel injector that isn't firing. Are you comfortable swapping the fuel injector from cylinder #1 with another cylinder to see if the code follows the injector?

You should also carefully check for vacuum leaks after the MAF sensor that may affect only bank 1, such as the manifold gasket near bank 1.

-Rod

Update
 

I don't think the injector is failing because when I switch out the #1 plug with a new one.... the truck runs perfect with no problems or CEL.... but after about 10 mins it goes right back to running rough and getting the same CEL codes again....

Ok, so look at a vacuum leak. Misfires and lean codes can be very closely related and either source can cause both codes.

I'm assuming that you shut off the engine when changing the spark plug, which gives the engine and associated components time to cool.

Fuel injectors use a coil of wire to open similar to an ignition coil, starter motor, electric fuel pump, etc. As with any electronic device, and vacuum leaks, expansion during heating cycles can cause open circuits. Similarly, when cooled, contraction can cause open circuits to close.

I'm not suggesting that I think a faulty fuel injector is more suspect than a vacuum leak, but I am suggesting that your theory is not sufficient to rule out the fuel injector, especially since in addition to the lean code for bank 1, you are also getting a misfire code for a specific cylinder. That suggests to me either an issue with the intake manifold for cylinder #1, an issue with the exhaust manifold gasket for cylinder #1, or a fuel injector for cylinder #1. Of the three, swapping the injector is probably the cheapest and easiest if you are doing the work yourself.

-Rod

Update
 

Ok well I traced all vacuum lines and found nothing... I took out the pcv valve and replaced it because it looked dirty... I put everything back together and started the truck... It ran like brand new... who would think the pcv valve would throw those type of codes.... so if anyone is having the same problems as me try changing the pcv first.....

That "usually" throws the P0171/P0174 lean on bank 1/lean on bank 2 as opposed to just one side.

Time to go
 

Well now that the truck is running good again it will be going on ebay Fri.... Time to move on