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96 f150 fuel pump question

southfork

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#1
I have a 96 ford f150 161k miles, on cold start it starts right up, runs fine, if I stop and do warm start up it starves for gas and diesels, I did pump pressure test today, both tanks only show around 1 pound of pressure, when it starts up the pressure comes up to 45 pounds, If I hit the drain pin on the guage pressure drops quickly to around 5 pounds, is it possible the pressure regulator is bad, I thought the pressure regulator controls pressue into the fuel injectors and not out of the pumps, or are both pumps super weak and the engine running increases the pressure?
 

southfork

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#3
Fuel filter new, right bank lean code, I replaced both o2 sensors. No misfires at all once it runs, as of late if Im sitting in traffic for a while it seems to want to stall out, but it seems like it's starving for gas.
 

Scorpio

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#5
common misconception, people replace 02 sensors when they get the codes, and yet, the 02 sensor is only doing what it is supposed to do, ie set a check engine when it reads a reading other than parameters.

right bank lean sounds like fuel to me also,

regulator there? pressures there?

sys too lean that side simply means the 02 sensor is seeing too lean a condition from spec, now the why?\


what about this:
If the codes were P0171 and P0174, the O2 sensors are fine, they are doing their job and REPORTING a lean condition. Most commonly a vacuum leak, with the PCV elbow being the prime suspect. Sometimes caused by a restricted fuel filter.
http://www.f150online.com/forums/v8-engines/407201-98-f150-system-too-lean.html
 

southfork

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#6
Code was 174, puzzle to me is low pressure with engine not running, Im leaning towardss the fuel pumps being bad or weak
 

Zilver

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#7
Before you start throwing parts at it; Clean Your MAF sensor

a common Ford problem
bad Mas Air flow sensor symptoms:
rough idle, excessive fuel consumption or not enough fuel reaching the injectors


Yes it still could be a weak fuel pump or failing pressure regulator, weak coil pack etc.
but MAF's can be cleaned so it will cost you nothing to try this first
my buddy replaced all of the mentioned items above which did not resolve the problem,
all he needed to do do was clean the MAF

how to clean:
http://www.fordf150.net/howto/clean-maf-mass-airflow-sensor.php
 

<SLV>

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#8
My vote is pressure regulator, but the first thing I do when an engine runs rough for any reason is put half a can of Sea Foam in the crank case and the other half in the gas tank. Run it 100 miles or so and see if the problem goes away.
 

southfork

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#9
Before you start throwing parts at it; Clean Your MAF sensor

a common Ford problem
bad Mas Air flow sensor symptoms:
rough idle, excessive fuel consumption or not enough fuel reaching the injectors


Yes it still could be a weak fuel pump or failing pressure regulator, weak coil pack etc.
but MAF's can be cleaned so it will cost you nothing to try this first
my buddy replaced all of the mentioned items above which did not resolve the problem,
all he needed to do do was clean the MAF

how to clean:
http://www.fordf150.net/howto/clean-maf-mass-airflow-sensor.php
Tried cleaning the Maf, even used maf cleaner. no good
 

southfork

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#10
My vote is pressure regulator, but the first thing I do when an engine runs rough for any reason is put half a can of Sea Foam in the crank case and the other half in the gas tank. Run it 100 miles or so and see if the problem goes away.
Never heard of sea foam, what is it, do auto part stores carry it, Im presuming its a detergent of some sort.
 

southfork

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#12
My vote is pressure regulator, but the first thing I do when an engine runs rough for any reason is put half a can of Sea Foam in the crank case and the other half in the gas tank. Run it 100 miles or so and see if the problem goes away.
I went to the parts store this morning to get the new Pressure regulator, got a can of sea foam and put in both tanks, Im about 15 miles from the store, on the way home I cycled between both tanks, when I got home and shut the truck off it started right back up on either tank, either a coicidence or some awesome product, either way I still suspect the fpr so will replace it since I bought it anyway and see what happens.
 

Zilver

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#13
I would keep TESTING
Check for vacuum leaks, look closely at PCV hose elbow for cracks,
check for air leaks between the air filter and throttle body
you can search for leaks with carb cleaner of propane (but be careful)
you may want to test the output from the maf sensor with a multimeter
lean codes can also be set by a bad EGR differential pressure sensor or a leaking egr
Good Luck!,
it's always a challenge tracking down these problems but persistence will eventually pay off

Ford P0171 & P0174 Lean Codes:
http://www.aa1car.com/library/ford_lean_codes.htm#
 

<SLV>

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#14
I went to the parts store this morning to get the new Pressure regulator, got a can of sea foam and put in both tanks, Im about 15 miles from the store, on the way home I cycled between both tanks, when I got home and shut the truck off it started right back up on either tank, either a coicidence or some awesome product, either way I still suspect the fpr so will replace it since I bought it anyway and see what happens.
Sea Foam is magic. Don't be afraid to run a pint in with your oil for about 500 miles before your oil change. More than once I've seen it clear up driveability issues.