2003 f150 xlt supercrew 5.4L

Our truck has p0171, and the shop who did a diagnostic said it was a bad MAF sensor because the Long Term fuel trims were too high. Current one is a oem sensor that we picked up from a pick-a-part several years ago. I'm going to try to clean it tomorrow, and go from there. I first want to ask if you guys have any good experience with aftermarket sensors(not motorcraft). I see on Rockauto there is Hitachi Brand for less than half of motorcraft which is same brand as oem on my nissan maxima. Any thoughts on that brand? any other recommendations? Thanks

 

I question your trust in your dealer diasgnostic.
First, a single code in not due to the mass air meter becuse the same air is passed for all cylinders.
Second is there only one code (171) or two codes, a 174 for bank 2?
If yes, likely it's not the mass air as stated above..
Third how far are both tables shifted?
If both are at 25% you have a common vacuum leak in the intake system.
Bottom line is you don't have enough proof it's the mass air sensor.at this time.
A replacement no matter from what source must work the same.
A Scanner looking at the Trims and the mass air signal should tell the story.
You don't have the full story hence the question of being the mass air meter until proven.
They seldom ever go bad.but can get dirty if the filter is not kept up with.
An exhaust leak at the header will cause the shift for that bank as well.
I am providing you with indepth info your dealer is not providing so you are not awere of it. They won't provide it when you refuse their service..
They want to sell you parts and service you may not need if it's an intake leak.
It's really not a matter of which mass air is better..
Mine is original has 320,0000+ on it and still going. The trims are a an avaerage ot 7% to the plus side. Just measured them two days ago.
Your call,.Good luck..

 

As far as I know, I don't necessarily trust them. it was not a dealer. it was local shop that had decent ratings on yelp and google. We don't have a shop that we necessarily have a lot of trust in.
it is just one code, p0171, it used to have p0174 as well but that went away after a new pcv elbow hose we replaced and some "adjusting" of the pcv hoses on their part. they cleared the code the first time I went
to them and we managed to pass smog check(CA) as soon as the emssions monitors cleared. SES light is not on, but with my bluetooth scanner I see that p0171 is still there. I also read the Trims
and if my scanner is correct, they hover at around 25%. Both. The air filter isn't changed "regularly", but we change it before it gets too dirty. When the "tech" at the shop told me, he didn't really seem too
sure. He didn't really say anything about the all the trouble shooting steps they took, and I don't want to ask a "tech" if he did his job even though we paid them. After all, they had the truck in their shop at the time. Truck passed smog and is running relatively fine
which is what we ultimately want.

 

If both long term tables show a shift to 25% they are adding fuel to the injection trying to counter what the OX sensors detect as too much Ox in the exhaust gas.
That is the basic loop detection system to keep the air to fuel ratio constant.under fault free conditions..
Look at the mass air reading; is it out of range?
Is there an intake leak after the mass air area that is letting air in as unmetered?
That it what is causing the shift in the tables.
Your diagnostic tool whatever it is does not tell you what parts to replace but the conditions in the systems.
It's up to you to see what the cause is, specifically.
If you were to clear all codes. then keep a check on how fast the tables shift it suggest how fast the fuel meteing shift is taking place and the possible cause such as a rotted or cracked hose, or a dirty mass air meter etc.
One code with both tables shifted is unsusal and suggest an exhaust leak on bank 1, otherwise both tables shifed has to set both codes as they operate independenly from their own responses to the two front Ox sensors.
I think your feeling challanged by my rsponses to explaining the operation but it's more complex that you are showing you know..
I can't help any more.
Good luck with the issue..

 

Like Bluegrass7 said.

This may help as well.

This code is triggered by the first downstream (front) O2 sensor. The sensor provides a reading of the air: fuel ratio leaving the engine's cylinders, and the vehicle's powertrain/engine control module (PCM/ECM) uses that reading and adjusts to keep the engine running at that optimum ratio of 14.7:1. If something is not right and the PCM cannot maintain the 14.7:1 ratio, but rather there is too much air, it triggers this code.

A code P0171 may mean that one or more of the following has happened: The MAF (Mass Air Flow) Sensor is dirty.
There could be a vacuum leak downstream of the MAF sensor Possible cracked vacuum or PCV line/connection Faulty or stuck open PCV valve. Failed or faulty oxygen sensor (bank 1, sensor 1) Sticking/plugged or failed fuel injector Low fuel pressure (possible plugged/dirty fuel filter!) Exhaust leak between engine and first oxygen sensor.
Even a loose clamp on the intake.

A lot of times, cleaning the MAF sensor and finding/fixing vacuum leaks fixes the problem. If you're on a tight budget, start there, but that may not be the fix for certain. So, possible solutions include: Clean the MAF sensor. Consult your service manual for its location if you need help. I find it's best to take it off and spray it with electronics cleaner. Make sure you are careful not to damage the MAF sensor and make sure it's dry before reinstalling.
Inspect all vacuum and PCV hoses, replace/repair as required Inspect all hoses and connections in the air intake system Inspect and/or test the intake manifold gaskets for leakage Check for a dirty fuel filter and proper fuel pressure. Ideally, you'll want to monitor short and long term fuel trims using an advanced scan tool If you have access, you may want to run a smoke test on your system. (A large cigar and the line off the brake side vac blow the smoke in and see where it comes out. Note make sure you have plugged the intake at the air throttle where that big plastic air tube clamps to the intake.)
The above is from the wide-open web.

Anyway, hope you get it fixed.

 

Thank you. I really appreciate your help. We installed a new motorcraft fuel filter two years ago, so I'm not to sure if that is too dirty. fuel pump was also replaced the same day but with a cheaper aftermarket one. pcv valve a bit longer than that, but since they are relatively cheap, we'll replace it soon. I'll also try cleaning MAF sensor as you mentioned. we did replace the pcv elbow hose which includes the hard hose that connects to the back of the intake. I'll go from there since the truck passed smog shortly after starting this thread. Again, I really appreciate your help.