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Ron, ASE Certified Technician
Category: Ford
Satisfied Customers: 35525
Experience:  23 years with Ford specializing in drivability and electrical and AC. Ford certs and ASE Certs
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f150: Check engine light on .

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Check engine light on .
Hello and Welcome to Justanswer, My name is XXXXX XXXXX I am here to try and assist your with your question.

What size engine do you have Please?
Customer: replied 4 years ago.
4.2. i know some of the newer motors with the plastic plentum has a problem with the bolt washers but this one is metal

Yes you are correct, the most common cause for the codes P0171 and P0174 on the 4.2 is a leaking upper intake gasket and or the isolator bolts, Ford has a redesigned gasket set along with new isolator bolts and Im willing to bet replacing them will resolve these codes. This is a very common problem. Its a very safe bet to replace the gasket as it should resolve this issue.
Customer: replied 4 years ago.
even the metal intake has that problem ? i even sprayed the intake with flammable cleaner and it didn't make a difference
Yes that is correct, but before you remove and replace the upper intake, take a close look at the PCV supply hose as it was also a know source of a leak due to rotting out. I would also try cleaning the MAF sensor with some contact cleaner. All three can and do set these codes.
Customer: replied 4 years ago.
pcv hose is ok and the maf sensor looked clean but i cleaned it anyway. i noticed its idling a little high too

Okay as long as you have good fuel pressure and no external leaking vacuum lines and a good working MAF then I would suspect the intake is leaking. The codes P0171 and P0171 are always lean codes Set by one of the three.
Customer: replied 4 years ago.
fuel pressure is at 28 at idle unless my gauge is off
Normal engine running pressure is 28 to 45 PSI so you should be fine Randy.
Customer: replied 4 years ago.
what should the maf be reading at idle
MAF BARO reading on scan data at sea level is typically 156 Hertz (Hz) plus or minus 4 Hz, and will go down by about 3 Hz for every 1000 ft. above sea level. BARO reading on scan data is NOT a sensor reading, but rather it is a calculation of vehicle elevation that is made by the Powertrain Control Module . The PCM calculates BARO mainly by looking at the MAF sensor reading at high throttle openings, and comparing the readings to base sea level readings that are stored in internal memory. As such, just cleaning or replacing the MAF sensor will NOT change the BARO reading. The vehicle must be driven at high throttle openings for the BARO reading to recalculate, or it can be reset by disconnecting the battery for about 10 minutes, or performing a Keep Alive Memory reset using a scan tool.
Customer: replied 4 years ago.
the customer did disconnect the battery then drove it normally for about three miles when the light came on again .
Well take a look at your MAF reading and see what they are. Its eaither a bad MAF or a vacuum leak.
Customer: replied 4 years ago.
maf is gr/se 3.48........... 4.01 @ 1100 rpm
That sounds about right depending on your altitude if your measuring HZ..
Customer: replied 4 years ago.
about 742 ish

If thats your altitude then its a bit high, level is 156 Hertz (Hz) which you very close to.

Customer: replied 4 years ago.
baro prs hg 26.3.........maf volts .68..... maf g/s 3.48
Baro HZ need to be about 156 or less at or below 1000 ft, if these are the readings you getting you have a bad MAF. I would start with installing a known good MAF.
Customer: replied 4 years ago.
yes used another scanner and its 147.59 Hz
Okay then that a good reading.
Customer: replied 4 years ago.
it must be the intake gkt . i put a new maf on and it set a learn bank 1 pending code again
I would have to agree. The older intake where also know to leak as well.
I would have to agree, the older intakes where also known to leak.
Ron and 6 other Ford Specialists are ready to help you
Customer: replied 4 years ago.
did u mean upper intake ( plentum or the lower intake gasket
In most cases its the upper that leaks but due to the age of the truck, if I was doing the job, I would do both.
Hello, Ron here again.

I am so glad you decided to come to Just Answer. It has been a few days and I noticed your previous visit here where I responded has not been completed and closed out.

I hope I met all your expectations and asked all the right questions and provided all the right answers. Please let me know if there is anything else I can assist you with. If needed I can try to clear it up or explain it more in layman's terms if not fully understood.

If you were confused with the rating system, just reply and let me know. If you thought you had completed the rating, but after getting this message realized it did not go through, reply and let me know.

Thank you very Much, Ron
Customer: replied 4 years ago.
its comming back tomarrow . ill let u know
Not a problem Randy, Im here if you need me.
Customer: replied 4 years ago.
it came back with the same code
Are you sure the cooling system is totaly full and no trapped air?
Customer: replied 4 years ago.
why would that make the lean bank 1&2 codes but yes it's full

Sorry, I had you confused with another truck Im working on, these codes usually mean you still have a leak. I can send you the factory pinpoint test if you want to run thur it. Start testing at H41 CLICK HERE

Customer: replied 4 years ago.
we did end up finding another vac t under the manifold that was leaking.
That would do it. The codes P0171 and P0174 are lean code usually set by vacuum leaks.