P0171 and 174 lean banks not the thread title
Chasing them down
Traced the vacuum lines, found one of the 4wd activators was not working so replaced both
Put 2 new check valves in
Checked box behind battery
Looked at hoses
Checked master brake cylinder hose
Ordered 2 new upstream O2 sensors
New EVAP solenoid
new maf sensor
changed fuel filter
Pulled Throttle body, cleaned it and replaced gasket
Any other ideas?

 

Based on the codes in your post header - my first idea is to ask if you have checked the clutch pedal position switch -- OR did you resort to the parts cannon because the truck is not a standard transmission?

 

I'm going to go on a limb and guess the op means p0170 and p0174 lean codes?
if there's no vacuum leak I think the next thing to do is clean the mass air sensor.

 

needsmoarturbo is correct. Fat fingers in a hurry. The codes are 171 and 174. Lean on both banks.

 

Maf ?

 

All that sounds parts cannonish to me
You guys ever heard of pinpoint test steps?
There is a whole rash of them in the H manual for those codes
That is why the PCED is called the H manual
The fuel system tests are in the H section
So, the first thing is to know what year and engine, then you can look at the correct PCED pages
Agreed, the tests are difficult if not impossible for the layman

 

I am aware of some of the tests but don't have the equipment. The truck is almost 20yrs old so I figured the parts won't last forever and might as well change them in pursuit of the problem.
Do you have anything of value to add as to what else to look at before taking it into a shop?

 

Get a scan tool that can at least read some live data or PIDS.
Check a few, then fire the cannon
For instance, that MAF should be around 1.3v at idle and go up to 3.4 or more when you punch it
Your front O2s should be switching above and below 1/2 volt
There are different values like pounds per hour and percents etc. you go to the library and use All Data
Get a reference PID value chart for your year and engine and test / check a few
That info is a bit deep in All Data, Use computers and control systems then diagnosis and testing
While you are there look or glance at the first few pages of the H manual data for those 2 codes

 

How I do it after all these years
Code test
Glance at the pinpoint tests
Run a few PIDS
Make a determination as to what part to replace or what to do first
I do this for a living still, so CYA is in there all over
We used to call our main drivability guy "The Wetherman"
Because "whether it fixes it or not don't matter because I am the weatherman"
You hit the dealer and they will say things like we got to start somewhere, and this might not fix it, give odds etc.
Good luck
Use Ford parts

 

What's the weatherman reference?
Actually, by going down a list and replacing parts I'm learning a great deal like replacing the 4,wd actuator. I'm not buying a scan tool for the same reason I don't buy a snap on torque wrench, the use vs cost just isn't there.