I have a 2001 XL F-250 pickup with the 5.4 in it. I have the infamous P0171 and P0174 lean bank codes. I have checked every vaccum line for leaks, cleaned and tested (with a multimeter for accurate measurements) the MAF sensor, changed the O2 sensors, and knocked out the cat. The truck still runs like garbage. It starts fine, drives and idles ok (maybe just a little rough but nothing bad enough to bother with) but when you rev it up or really get on it while driving, its terrible. It will not rev up to full RPMs, it pops, missfires, and doesn't seem to shift right, and when you floor it from a stop it bogs down and will not want to move out of its own way. The only codes im getting are the "lean bank 1" and "lean bank 2" so i don't know if COPs would cause this or not. Also, I looked for any blown out spark plugs and they are all in tack.
On my 98, there was a vacuum boot at the very back of the engine, center, near the top that leaked. At the time I recall it was a common occurance. It's not easy to see, I ended up changing mine strictly by feel. Check it out, and let us know what you find.
Sounds like it could be a fuel supply issue. Have you checked the fuel pressure at the schrader valve on the injector rail? It should be roughly in the 30 to 40 psi range and increase slightly under load. If it is low and/or falls off under load, there's your trouble. Could then be a bad fuel pump or plugged fuel filter.
I forgot to mention that the first thing I did to the truck was change the fuel filter. The old one looked pretty bad but the new one made no difference in the performance. I have checked all the vaccum hoses but I will check the ones curving back behind the engine again. What will I need to make a guage work on the schrader valve?
You would need a fuel pressure test gauge. I got mine from Tool Topia, but I've seen them at Amazon.com and other places also. Your local auto parts store may even have them. Generally they are less than $100 and come with a gauge, a reasonably long hose, and various fittings and adapters to connect to schrader valve and other types of spigots. I like to have the hose long enough so that I can place the gauge up on the outside of the windshield if I want so I can drive around with it visible and test under heavy load.
I did not get a fuel pressure gauge last night but I am going today to buy one. However, I did recheck all the vac hoses and they are still good. I also took off the IAC sensor, cleaned it, and put it back on. took the truck for a drive and problem fixed!.....for about 2 miles then started doing the same thing again. I wasnt watching the temp gauge but im wondering if it acts up when the engine is warm. Also, when the truck starts to act up and bog down and sputter, the lights dim. They dont go out at all but its very noticable, almost like going from high to low beams. I thought that was odd. Any other ideas? like I said i am going to get a fuel pressure gauge today.
You need a volt meter even more than a fuel pressure gauge. What is the system voltage when it's running poorly?
I haven't checked that but I can tell you the alternator is maybe 5,000 miles old and the volt meter doesn't really drop when this happens. You can just see the lights dim in front of you as you feel the power just fall off.