so.....I have a 2004 f-250 superduty, 5.4 4x4. Have had a problem with power-loss, and stalling issues. If I am going say 55-60, all of a sudden she will start to shudder, and I have to "throttle thru it", or when I come to a stop, SOMETIMES rpm's will drop to 500, and feels like she wants to die. I cleaned throttle body, replaced IAC, replaced MAF, tested fuel pressure(was good), used propane and throttlebody cleaner to try and find any vacuum leaks, and have two damn good mechanic buddies who are up in arms about it. any ideas? anybody experience this crap? PLEASE HELP!!!!! Whatever it is, it is shooting of a lean code for both upstream banks. If it were a vacuum leak, would'nt it happen constantly????????

 

There is always some guy like me that will ask some dumb questions like when were the plugs last replaced? And what brand of plugs were installed? Somehow the basics always get into the picture and until they are known or checked any other suggestions may or may not be worth anything. Crazy things like windshield leaks cause unbelievable electrical problems. Vacuum hoses can get soft and collapse when hot and sometimes even come off. Computers have a great ability to compensate for some problems , but not all. Always a good idea to check all the fuses because certain parts that control/influence performance are protected by fuses.

 

have thoroughly checks vacuum hoses/lines. Have not changed plugs, but only has 32k on it. I know, I know, they could still be bad, but I really don't believe this is a plug issue. I did, however, relieve some gas from pressure relief valve on pressure tester into a glass jar, and it looks freaking terrible. Now I know that clogged injectors would give me misfire codes, but how about very crappy gas........Very yellow, not too watery looking, but very "rusty" looking. thinking about dropping tank, to empty out old, and put in new. This truck almost definitely sat for very long periods of time, since '04, and only 32k on it.....I bought it at 28k...what do you think? If gas is "watered" down enough, but not enough to throw misfire codes, would real bad gas give me a lean condition? Me thinks so

 

Me thinks you are correct !! Bad/ contaminated gasoline can do all sorts of bad things.
I would consider replacing the fuel filter and see just what comes out of the old one.
That could answer a lot of questions. Even if the plugs have low miles on them, might also be a good move to replace them with new Motorcraft plugs considering the possible fuel problem. The original are probably platinum electrode and would normally last more than 32K ,but plugs don't always last/perform as long as the hype we hear.
Let us know how you make out on this, thanks.

 

I'm taking a break(lunchtime)......and just got done dropping the tank. Just now checked the ff, and I'm glad you agree this is at least a possibility. Thanks for the input.....I'll let ya know if it works!

 

well.... fuel tank was rather clean, and fuel wasn't near as bad as I thought, so .....back to square one! silly question time!!!!!!!-Could a shot exhaust manifold gasket(s) cause a lean condition in both banks? cause she's got the tick that just reminds me of an old farm truck....I'm quite sure atleast driver's side manifold gasket is crap. whatchathink?

 

is there an egr system component that I may be overlooking.......but I thought EGR was for Idle and start-up operations????? yes/no?

 

The EGR system is non-functional at idle. That means the EGR valve is supposed to be closed at idle. If open any amount at idle , it will affect idle quality. Sometimes a piece of carbon will get stuck under the valve pintle and prevent it from closing completely.
Exhaust leaks can affect oxygen sensor operation which in turn can affect engine performance. Best to correct before getting into anything else.
There is a list of things that could be causing the problem, but does either of your buddies have or have access to a decent scan tool? If so can you get some data and let us look at it?

 

Would like to know what the fuel trims are at idle and 2500 RPM.
Also, what are the IAC counts/% ?
If you can try to check the plugs going to the PCM for water intrusion.

 

thanks hanky....will collect this data, then get back at ya.