My F150, 5.4L and 75000 miles has been giving me 2 trouble codes.
P0171 System too Lean (Bank 1) and P0174 System too Lean (Bank 2.
I had the fuel filter replaced, injectors cleaned, and a new air filter. It is still giving me the error code. It runs great when it's cold but when it warms up and i'm waiting at a light the tach drops to 500rpm and it starts idling rough. Any help would be really appreciated!

Thank you

 

Try cleaning your MAF (Mass Air Flow Sensor). If it's dirty your engine mass be taking in more air than the MAF is measuring.

You can clean it with a Q-Tip and windex.

 

AJ..

The MAF has two very small filaments. If I touch them with a q-tip they would break for sure. Any other ways to clean it??

 

A friend of mine with a 97, 5.4 used a spray can of carb cleaner on his and his wifes Thunderbird. It didn't seem to hurt anything so I did it on mine. Like a Timex Watch, keeps on ticking.
I have read that this should not be done but, it works okay in our cases.

 

JUST DO IT!!!

If you do a search on MAF in the Engine section, you'll find that most of us have done this at one time or another. Although it is delicate, you won't break the wires if you don't push hard.

Take a Q-Tip and spray either some windex or electrical contact cleaner on it and gently rub back and forth across the MAF. Do this with a few Q-Tips and allow it to air dry before reinstalling it.

 

Well cleaned the Mass Air Flow sensor. I still have the same problem. Any other ideas??

 

It may be the Idle Air Control Valve is sticking. The low RPM's suggest this.

I should have brought it up before. Next time this happens, if it's convienent, tap the IAC with something like a screwdriver and see if it frees it up. I'm not certain of where it is on the 5.4L but it may be mounted on top of the throttle body.

 

Your O2 sensors may need replacing - they sense the exhaust and tell the engine how rich to run. Thet're supposed to be good for 100k but some fail earlier.

 

ntxt

 

n/m

 

Well I finally got around to looking at this problem again. I looked at the Idle Air Control Valve. It looks more like a spring loaded plunger on a solenoid. With no power to it it's about 1/2 way open. With power to it it's 1/2 open. And I tried to turn over the engine but it runs for about 5 seconds and dies with the Idle Air Control Valve off of the manifold. I ohmed out the Idle Air Control Valve and it was about 9ohms. If it's a coil it should read low.. Any other ideas??

 

Well when you recieve two lean codes it has indicated that the your complete system is on lean. Getting one lean code such as 0171 lean indicates a problem, something as simple as one misfire. When you get dtc (code) po0171 and dtc po174 that means that the sytem is at the rich correction limit. You have indicated that it runs great when cold and runs rough when hot meaning your computer is going into closed loop. I am guessing that you gas milage rather poor, but is there any other symptoms that you can give, and i might be able to help you. With out haveing a scan tool and knowing exactly what it is doing it leaves to many variables to what exactly it could be. I am asumeing that you have a code reader and that you can clear all dtc(s) (codes). If you can, clear all codes. Then disconnect your fuel vapor hose at the intake mamifold, and plug off the vaccum leak on mainfold. Start engine and run untill the computer goes into closed loop, (ussually 2000 rpms for about 5 min). By doing this it will determine if it is lean because of a low fuel situation, or a high or low air situation resulting in you leanness, and should give you diffrent dtc(s). record what they are and reply back to me and better determine what route to you send you on.

I am ford certified mechanic and use ford terms often and get carried away sometimes, so if I didn't explain soemthing to well let me know. i tried to out it in simple terms.

 

I had this situation happen a few times before. One the customer ran it out of gas and relived all residual preassure in the tank, which is a requirment for obd II sytems. leaveing the gas cap off for a long time or leaveing the gas cap loose can also releave the preasure.

another was a bad pcv valve, when i was in training, i was amazed at how a simple thing like leaveing the dipstick tube off, was enough to set those codes. also simple thing like a vac. leak or intake leak, bad plug(s) wire(s), exhaust leak, leaks at mass air flow sensor, are some of the simple things that set the code.


I think that your problem is a fuel preassure problem, but we will determine that when we see what codes arrive after you complete what i have indicated above.

just another question, i assume you had a shop do the work indicated and that they cleared that code. That will not leave until 30 cycles, meaning it has to be warmed up and fully cooled off 30 times, unless cleared by a scanner. or disconnecting the battery, caution on that though, your truck computer uses adaptive stategy, which adapts to your driving habbit and wear to your vehicle , by disconecting your battery, it will loose memory and may run diffrent for you for sometime. if you drove the truck like it was before you had the work done to it, for sometime it may have addapted to that condition, and can be corrected by diconnecting the battery. I have seen that happen too, but very unlikely for your situation unless you drove it for sometime uncorrected.

well let me know just a little more info