Hey so I have a 2007 ford f150 5.4 and I'm trying to figure out why after I drive for a while my engine looses power. It's throwing me codes: p0171, p0174, p0191, and p0301. Anyone what could cause these codes to show up at the same time? I also get a flashing check engine but it goes away if I stop the truck. Thanks.

 

Cylinder miss fire. You need a tune up.

 

@Bkruano - you are one lucky dude. Your multiple OBDII codes have a common thread leading to the same diagnosis. First let me mention that a flashing CEL is a special circumstance. It's the ECU's way of telling you that a potentially CAT damaging situation exists. THAT'S BAD. But in your case it connects the dots on the other codes.


a.) P0171 (lean Bank 1) - P0174 (lean Bank 2)
While there are other possibilities when you get BOTH these together, its freequently "intake air leaks", Faulty "MAF", or Faulty "PCV". Your 5.4 doesn't have a PCV valve, so we can eliminate that one real quick. Both "intake air leaks (cracked manifold - bad gasket)" and Faulty "MAF" are not uncommon on your 5.4. Either of these can (and usually) drives Fuel Trims up, dumping excess fuel into the combustion process - and WILL cause O2 sensors to sense excessive hydrocarbons resulting in a flashing MIL, especially under load.


b.) P0191 (Fuel Rail Pressure Sensor Circuit Range/Performance)
On your 5.4, fuel rail pressure is "relative to IM Vacuum" as determined by a little vacuum line running way down low on the rear / passenger side of the Intake Manifold. While other possibilities do exist, certainly a Vacuum leak, or a problem with that little vacuum line, screws up the value the sensor delivers to the ECU. That effects injector pulse width and fuel flow. It is evidenced best by positive fuel trims as the ECU commands injectors to deliver more fuel to compensate for EXCESS AIR or incorrect MAF air flow reading - and WILL cause O2 sensors to produce readings resulting in a flashing MIL.


c.) P0301 (Cylinder 1 Misfire detected)
While other causes exist, a vacuum leak as well as flooding with fuel is certainly a possibility. You probably have misfires on other cylinders or "random misfires". And "misfires" send unburned hydrocarbons into the exhaust and WILL cause the O2 sensor to report a catalyst damaging situation.


I am not disagreeing with @Rnlcomp. You need a tune up. Plugs for sure if they have many miles on them. To start narrowing things down, I would try to obtain live OBDII fuel trim values to see if one bank is worse than the other (probably not with both lean codes). Then look for a vacuum leak (spray starting fluid or carburator cleaner all around the intake manifold - particularily down the fuel pressure sensor vacuum line) - while monitoring fuel trims / O2 sensor signals if possible - or just listen for a change in idle.


If a vacuum leak can't be found, I would invest invest in a MAF new sensor and clean the TB. If the truck has 100K or more miles, I would invest in all four O2 sensors. I am a firm beliver in changing O2 sensors preventatively around 100k miles. They get "tired" and "calibration" drifts.


But don't let the flashing MIL situation continue. Things will deteriorate fast.


Good Luck

 

Flashing CEL = cylinder misfire, p0301 = cylinder 1, cylinder misfire can and will make all the other codes occur.

Fix the misfire and all the other codes will vanish. Unless there are other problems like a vacuum leak etal.

DO NOT replace the MAF sensor, that's just throwing parts in an attempt to alleviate the problem.

Of the over 30 years I have been a tech (11 as a Ford line tech) what I posted is the norm.

 

THAT, I'd have to agree with.

For full disclosure, my qualifications are meager by comparison. Outside the shade of my tree, I barely know which end of a monkey wrench to use. But I respectfully have to disagree with this part of this paart of the NORM, as I can find no nexis between cyl 1 misfire being the cause of P0191 code - without subscribing to a "multiple simultaneous failure" theory. And while misfiring is one thing that can cause a Flashing CEL, I need an explanation how Cyl 1 misfiring can cause a lean condition on both banks ???


So I thought spraying a little ether around the manifold would be a NO cost way to confirm or eliminate my shade tree diagnosis.


No offense intended. I'm still learning.

 

Totally blanked on the bank 2 lean code, that would normally be a vacuum leak, probably the intake manifold O-rings, old age they get hard and lose sealing.

Main thing to concentrate on however is the flashing light, get that fixed before attempting to diagnose anything else, I've seen some weird things happen and ghost codes pop up that are completely unrelated in ways you would think abnormal.
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