Vehicle - 2003 E250 with 5.4L and 292k miles.
This issue has been kicking my butt and I am hoping that someone will have an idea of something that I night have missed.
DTC showing is P0171 And P0174 Lean on both banks.

At idle
The LTFT show very high on both banks 27 - 33
The STFT looks great and bounces between +/- 7 at the most.

The LTFT goes down in relation to how open the throttle is open (or you could say, engine load) But It stays high at freeway cruising.
The idle is generally good with some minor fluctuation. Pickup is generally good as well. Drive-ability is good too.

It all points to a vacuum leak. I had heard that people had issues with the upper manifold gasket leaking so I took the opportunity to go ahead and replace the upper manifold with the newer design with built in gasket and improved cylinder branch paths. No change.

I looked for hoses that were old and cracked and replaced a few. No Change

Did a smoke test and found no leaks except a very small leak around the EGR plunger. Went ahead and replaced the EGR valve and it made a very small change of maybe 2-3 points on the LTFT (After a computer reset) Also found that the vacuum line for the ac vent dampers was leaking so I just plugged it and it might have made a 1 point difference.

Since I found no leaks during the smoke test I started to look for other issues.
Cleaned the MAF no change
Swapped out the MAF with the one in my other van no change
Replaced brake booster hose no change
Temporarily blocked the brake booster hose to check for leak in brake booster itself no change

The following additional components have also been replaced
IACV (It was making an annoying humming sound. Now it's just the usual "air rushing" sound.
EGR Pressure Feedback Sensor
EGR Valve Control Solenoid

Even though the smoke test did not turn up any issues, I went ahead and sprayed starting fluid around the whole engine (when running cold) with no change in speed or o2 sensor reading.
I sprayed a little in a vacuum line and watched the o2 sensor voltage peak on my real time diag tool.
I went ahead and replaced one of the o2 sensors with a spare I had around and there was no change
BTW, since this is a 2003 year model, it has 2 upstream o2 sensors and ONE downstream.. (in 2004 they changed to 2 upstream and 2 downstream sensors)

Next I went ahead and tested the fuel rail pressure and it was consistently within spec at 30 - 40 psi (40 psi under load 32 at key on and 30 at idle)
BTW, I replaced all of the fuel injector seals on the manifold side when replacing the upper manifold.

If anyone has any ideas on anything else I can look for I would greatly appreciate any input.
This has been driving me crazy and I really can't afford to lose any more hair!

Thanks!

 

Great explanation and thorough work so far .. I too had same codes and swapped out the In manifold and whilst in there did similar precautionary maintenance (mileage 295k)
I know this sounds off the wall but how is the battery ?
I had a chevy pick up that used to throw a code over and over despite me rectifying the apparent issue. I read somewhere that a battery in sub condition can cause weird symptoms and I changed it out and the problem disappeared.
just a suggestion.. it sounds like you’ve covered the usual issues.
one other point is I’ve heard that the dormer type replacements can still leak
(ask me how I know)
habe you monitored the coolant level Closely
keep us posted

 

Did you get a chance to check the vacuum reservoir for rusting thru and causing a vacuum leak?
"Tomato juice can mounted" on the fender well.

 

Hanky, Thanks for the reply.
Are you referring to the "can" that is part of the vapor recovery system?
I temporarily blocked off the vacuum line to the recovery canister with no change.

 

Britman, thanks for the reply.
Yes, the battery is fairly new and in good condition.

I do not think the codes are arbitrary as the engine does seem to run like it is fighting a constant lean condition.

 

Since I had heard that clogged fuel injectors could cause a lean condition, I went ahead and ran a bottle of fuel injector cleaner through the gas tank and saw no change at all. I figured that if this were the cause that I would at least see a small change.

 

Sorry I couldn't get back to you sooner, but the "Tomato Juice can" is the vacuum reservoir and if it has rusted thru it will cause a vacuum leak and possibly some problems with accessories that rely on vacuum for correct operation.

 

Hanky, thanks for the reply. I have not seen the tomato juice can since mid 90's F150s and the like. And it was the vapor recovery canister that was filled with charcoal. I blocked off the vacuum line to this with no change. The other vacuum canister that I know can leak is for the HVAC system and I also blocked off the hose to that reservoir with minuscule change as previously noted.

 

You are right . The can is there on F series . There should be a vacuum diagram under the hood lid or in the engine compartment. Does it show a reservoir?

 

Probably looks like a plastic ball about the size of a softball.