Hey guys! Been battling the lean codes for about a week! 2001 f150 5.4l 121xxx miles

So here is the situation. The truck runs perfect above 60 degrees outside, however when it gets in the 50s or below it will start up, run 1300rpms instead of the 1100rpms its supposed to, then die down slowly to 800. When it reaches 800 the rpms start to jump back and forth between 650-800 in a loop for about 10 seconds until the truck decides to kick itself back up to 850 to hold steady. This will happen a few times over 5 minutes while it warms up. While driving and coming to a stop, it will hesitate to idle as well until it has been driven about 10miles and then its fine.

I've repalced the entire PCV system, intake and ALL hoses are new, and hose clamped as tight as can be. TB/TB elbow and EGR all removed cleaned and new gaskest. IAC was replaced with a motor craft one, new gasket of coarse. Unrelated ALL new plugs, rear 02s are turned off so they cant be messing with it.
I have an SCT x4 tuner and have been watching the STFT and LTFT on both banks non-stop and on normal days my LTFT seems to run 1.03-1.14% on each bank back and forth depending on idle loop/load. WOT its 1.00 at all times. During the cold weather, the LTFT on both sides reaches 1.25% when idling at a stop. Today is the first day I didn't get a CEL, but if I understand correctly if it hits 1.26LTFT that light will pop back on. Even without the codes, I'm still having the idle issue on start up and hesitation in cold weather. I also noticed the intake temp is exactly what outside temps are and I wanna say I read before that it should be reading higher then outside air temps. Any ideas?

 

You need to do a smoke test to see where the vacuum leak is.

 

171 and 174 are NORMALLY vacuum leak on the left and vacuum leak on the right.. Something related to the manifold or egr system.. BOTH SIDES COMMON... mine was the two small 1/4 inch ID hoses about 8 inches long above the drivers side valve cover on the EGR system... I know you said you did all hoses, but something is still leaking... common to BOTH sides.

 

I'm LEANING towards intake manifold gasket the more I read. Seems like there was a huge post about it and a few people that dealt with it for years before finding that fords initial gasket was a POS and would have holes burn up in it... On top of that, its 16 years old and in texas heat so. If that doesn't do it, last 2 things I can think to check are fuel pressure, and MAF sensor though my SCT x4 shows MAF counts to be stable so I doubt it is the MAF.

 

Are you talking about the tiny little plugs that slip on and off, below the egr and right in line of eachother?

 

Added note that I should have stated probably. On start up this morning the STFT was .75-.94% which i believe means its running "Rich" , so its removing fuel, but the LTFT is saying its LEAN running 1.25%.

 

I had two 1/4 inch ID hoses ( approx.) that were about 8 inches long... above the drivers valve cover - as part of the EGR system... I assume they got over hot by being in the vicinity of the EGR tube or exhaust manifold... Brittle and hard / cracked when I took them off to look..


Im sure the intake manifold gaskets COULD be a problem, but you don't hear much about that on the 5.4 motor.... I have heard about it on the 4.0 V6

 

I don't understand your fuel trim readings. AFAIK, fuel trims are not into decimal numbers. If the fuel trim is negative, the PCM is removing fuel. If the fuel trim is positive, the PCM is adding fuel.

When the PCM is adding fuel, it is trying to compensate for a lean condiction. If the sum of the STFT and LTFT exceeds roughly +30% the PCM will set P0171 and/or P0174 code.

Maybe the 1.xx% readings have something to do with the scan tool you are using?

 

Take the decimals out, SCT X4 scanner puts them as decimals, but basically .94 = 94% 1.25 = 125% which would make 1.00 or 100 desirable "0%"

 

Oh, okay.
So 0.94 = -6% (PCM removing fuel) ?
And 1.25 = +25% (PCM adding fuel) ?

 

You got it bud.

 

When you get the light, look at the freeze frame data and see at what the rpm and engine load was when the fault occurred.

Fuel trims can be tricky to decipher. Ford actually uses a 9 cell fuel trim array. Think of a grid with three rows across the top representing low/medium/high rpm, and three cells vertically representing low/medium/high engine load.

When the scan tool asks the PCM to display a fuel trim, the PCM displays the fuel trim cell that the engine is currently operating in. If you are seeing 25% LTFT at idle, that is not enough to trip the P0171/174 codes. But if the freeze frame data shows that the code gets set at heavy load, you wanna see what the fuel trims are at that load. Typically a 171/174 code that pops up under heavy load you should want to be looking at fuel supply issues.

BTW, you may be looking at two different issues.
Just sayin........my $0.02 worth.
Good luck.

 

Appreciate the feed back. The truck in park eventually flat lines at 0% after 15minutes idling in PARK. Both STFT and LTFT stays 1.0 or "0%". WOT is also flat line 0%. its letting off the gas that will trigger the CEL after being on the throttle i'd say 4/10ths of the way. However idling in drive its always +9 - +21 in the morning. After sitting for 8hours at work and its warmed up for the day the truck starts and runs just fine never goes past +8%.

 

When you say it flat lines, especially at WOT, me thinks it is no longer in closed loop.
Can you confirm?

And Is the coolant temp appropriate?
And Is the TPS voltage appropriate?
If they are out of wack, it might go open loop.

 

Voltage tester is not in my tool arsenal yet so i couldn't tell ya. However coolant temp reports around 220 last time i checked