I have about 45,000 miles on my 03 gas only 5.4L which just started acting up. (Sits around in the garage because I'm retired. Drive it two times a week about 8 Miles only).
Replaced DPFE, EGR, EVR, PCV already and inspected the PCV Elbow and hasn't fixed it yet. I also cleaned the MAF with Electronic Cleaner (MAF has NOT been replaced).
I have no fuel pressure instrument to check that. I disconnected the vacuum line from the Brake Booster and PLUGGED the hole and fired it up but that made no difference (Hesitation on accelerator pedal pushed, back fired etc.)
I could have a vacuum leak on some hose but I haven't found it yet. Last I see here in the forum that I could have a bad Intake Manifold Gasket. Wouldn't those normally go out and cause a single P0171 or P0174 code say if one port was leaking or is the computer not smart enough to distinguish between left and right bank and by default posts both codes cause it can't make that determination? What's the failure mode on the gaskets (Mass failure or individual ports?). It's been hot here in Texas so that may have been a factor in causing the failure (whatever it is). (No temperature related issues noted as far as Engine Temp. indicators however).
I'm looking for any suggestions on what to try next? I guess I can get it to a shop as it seems to run once I get it up to 40 or so MPH. It's a challenge getting it out on the highway with its sluggish performance. Also replaced the FUEL filter.

 

Hello, The two codes are indicationg the same trouble because the trouble is common to both banks.
From your discription of such poor performence, it seems there is a massive air intake leak after the the Mass Air meter as unaccounted for air.
The OX sensors detect this excess air and try to richen up the fuel in an attempt to self fix the problem.
With such an air leak i'm supprised you don't have poor idle as well.
It could be lack of fuel as well that results in the excess air being detected. A check of fuel pressure would tell.
Look again at all intake areas for a rubber fitting cracked or split, throtle body mounting, I.
I would clear the codes and see what comes back so you have the latest history after doing the work.
It may take some drive time to allow the system to detect all faults as many are not detected instantaniously until tests are made and results out of limits set codes.
That is your way of working on the problem.
A dealer will use a scanner not only to see the codes but to view the real time operating conditions that should lead to a place to look for the problem.

 

The two codes are the result of the same issue that is common to both banks.
With the poor drivability you have, i'm suprised you don't have an idle problem as well.
Seem it is a large intake air leak or very low fuel pressure.
Look the intake hardware over again and feel each rubber fitting where you can't see for cracks, splits or deterioration.
Throttle body bolts and gaskets for air leaks.
Mas Air meter to throttle body large hose for being seated.
Check fuel pressure at the fuel rail for 35 to 40 psi while at idle.
Good luck.

 

Welcome to the forum.
Intake gaskets are not a known issue. I actually haven't heard of any failing now that I think about it.
Did you check the PVC elbow on the rear of the intake manifold too? That's the one that usually causes problems. Mine failed on the 01 F150 that I had at 32K.
If that's not it. I would suspect dirty injectors from sitting, or possibly low fuel pressure.
The O2 sensors monitor both banks independently. So unless a intake gasket failed on more than one cylinder, then it wouldn't trip both sides.

 

Thanks Bluegrass 7: Yes I had the Elbow off and inspected it. Couldn't find any holes in it. In fact I took pictures of it and the part number stenciled on the side of it (Just in case).
I put some FUEL Injector Cleaner in the truck but haven't had it running long enough for that to push on through the system to see if that helps. Short of the injectors I could have a bad fuel pressure issue?? I'll research how I might troubleshoot that next I guess (or go buy a fuel pressure gauge to check it).
I appreciate the guidance about the Intake not being a primary culprit and the details that LxMan1 made about the O2 sensors not likely to be bad with both banks reporting the same Lean burn.
Thank to both of you; I'll reinspect the air intake components and the vacuume lines again. Maybe a "Tee" is broken on the bottom side or something away from view. This is a lifetime garaged vehicle so it's been a bit protected from the elements. I'll keep hacking away, something is bound to make sense sooner or later.

 

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