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Chris (aka- Moose)
Chris (aka- Moose), Technician
Category: Ford
Satisfied Customers: 45021
Experience:  16 years experience
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2001 ford f150 5.4 vin L P0171 P0174, LTFT's are 10-15 at

Customer Question

2001 ford f150 5.4 vin L P0171 P0174, LTFT's are 10-15 at idle then max out to 25 anything off idle. Fuel pressure is 33 at Idle then rises to 44 at WOT or when fuel regulator vacuum hose is taken off. I've replaced the DPFE unit, fuel pump relay, fuel pump, spark plugs and intake manifold gaskets. Any ideas?
JA: How many miles are on the vehicle? And when was it last serviced?
Customer: 175xxx just bought it as a beater, codes were there when I picked it up. Changed oil 1st day I had it
JA: Are you fixing your F150 yourself? What have you tried so far?
Customer: Yes I'm a certified Honda/Acura Tech but little experience with Fords. I listed everything I did on the 1st post
JA: Anything else you want the mechanic to know before I connect you?
Customer: Not that I can think of
Submitted: 15 days ago.
Category: Ford
Expert:  roy replied 15 days ago.

hello, my name is ***** ***** I will be glad to assist you. please allow me a couple of minutes to gather some basic info.


Customer: replied 15 days ago.
sounds good
Expert:  roy replied 15 days ago.

ok, first, the fuel pressure is below spec and will cause both these codes. the spec is 35-55 idle.

when the hose is removed it should jump up about 10 lbs. the pressure with the hose on will rise as the engine rpm goes up as there is a loss of vaccuum to the pressure regulator.

other causes

1. pcv stuck open

2 vacuum leak, most common is intake manifold

3, mass air flow sensor

4. fuel pressure

I would start by getting the fuel pressure up to where it should be. it will take replacing the pump and filter


Customer: replied 15 days ago.
I replaced the fuel pump already
Customer: replied 15 days ago.
What specs did you find for pressure?
Expert:  roy replied 15 days ago.

your pressure is not correct for the specs.

I just posted the specs. did you not see it???

Customer: replied 15 days ago.
I see that so what do I check if the pump was replaced?
Customer: replied 15 days ago.
I also replaced the fuel filter
Expert:  roy replied 15 days ago.


Expert:  roy replied 15 days ago.

you may have a bad new pump. what brand did you use???

Expert:  roy replied 15 days ago.

what was the pressure on the old pump???

Customer: replied 15 days ago.
Did you find pressure readings on alldata? If so can you send me a screen shot or something like that? Delphi, pressure was on both pumps was identical.
Customer: replied 15 days ago.
pressure did jump to 44 when vacuum hose was removed from regulator.
Expert:  roy replied 15 days ago.

no, mitchel

Expert:  roy replied 15 days ago.

barely within specs

Customer: replied 15 days ago.
When I replaced the old pump there was a nest above the fuel tank, I inspected all connector/wiring on the frame rail but did not find any signs of damage. Does mitchel have any troubleshooting for a situation like this? I searched alldata but could not find any.
Expert:  roy replied 15 days ago.

the trouble shooting is the pressure test.

did you check the pressure in the old pump???

Customer: replied 15 days ago.
Looking for some kind of Ford and or Mitchel troubleshooting chart, I did find a TSB for checking for vacuum leaks, followed that one and did not have any issues with vacuum
Customer: replied 15 days ago.
I checked pressure at the fuel rail via the shrader valve
Customer: replied 15 days ago.
did a before and after pressure of old and new pump was identical
Expert:  roy replied 15 days ago.

how did you verify no vacuum leaks??? the intake is the most common failure. how did you test the pcv and mass air flow??

Expert:  roy replied 15 days ago.

ok, so you also believed the old pump was bad because of the pressure readings.

I still think you have an issue with the pump.

Customer: replied 15 days ago.
There is a Ford TSB, basiclly monitor STFT and LTFT at idle and 2500, compare total correction %, the tests passed. Smoke tested the intake system as well for good measure, no leaks present. PCV removed cleaned with carb cleaner was in very good shape did not know how to test it is there a procdure for that? MAF I can graph/monitor that with my scan tool it is reading correctly compared to throttle position.
Expert:  roy replied 15 days ago.

ok, that sounds good. the test for the pcv is to remove it and put your finger over the end and see if the long term trim drops. if it does, it is no good.

the only thing left is the fuel pump.

Customer: replied 15 days ago.
the pump, all the wiring leading to the pump and possibly a restriction in the lines. Can you find any electrical tests for the pump-voltage/resistance at the connector, a way to jump the pump then check pressure etc. I can't find any testing info on the pump side of things short of replace then recheck pressure
Customer: replied 15 days ago.
I'm ruling out I may have installed a faulty pump but to replace a pump then have the same exact reading makes me question at the very least the power going to the pump.
Customer: replied 15 days ago.
I'm not ruling out I meant to say
Expert:  roy replied 15 days ago.

ok, it is obvious that you and me are not on the same page. I give opinion based on your input. I am not there and cannot touch feel it or see it.

I am opting out since you are not taking my advice. my suggestion is to give whoever follows me the benefit of the doubt that they know what they are talking about.

happy new year


Customer: replied 15 days ago.
I need more information about wiring at the pump
Customer: replied 15 days ago.
How can you not be on the same page? PSI was 33 old pump, install new pump 33 psi. Next step logically would be to check wiring correct then check for restrictions in lines like some kind of flow test correct?
Expert:  Chris (aka- Moose) replied 15 days ago.

Welcome, I'm Chris (aka Moose), my normal schedule online is around lunch and after dinner till early morning.

Would you like me to try and help, if so can you list out each ( 1)_____?) question you need answered?

Customer: replied 14 days ago.
please, just looking for direction here. I replaced the fuel pump but still getting the same pressure readings so my next step should be to make sure the pump is getting the proper voltage and there is no high resistance in the circuit but cannot find any guides to do so, Can you help?
Expert:  Chris (aka- Moose) replied 14 days ago.

If you want to verify good power and ground to the pump then you must do so right at the pump connector on the fuel tank.

While the key is on and the pump is running you should get battery voltage on the pink/black wire and no resistance to ground on the black wire.

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Customer: replied 13 days ago.
Thank you so much for your response, sorry for my late response. I won't have time to check it till Friday (single Dad, work long hours). When I looked up fuel pressure specs it showed 28-55 psi at idle so if I'm reading 33 psi I should be ok right? One thing that I'd like to have your thoughts on. My scanner reads both LTFT at 9-14 at idle then maxes out at 25 anything off idle. If it was any type of vacuum leak LTFT should come down to normal off idle correct? Another thing my scanner can also read/graph my MAF but I do not know what scale it's reading, it reads steady then goes up and down when throttle is applied but the scale reads from .7 to 15 (.7 at idle then if I do a wide open throttle snap 14.8 is max) I'm not too sure if its reading too much air? Thank you again for your time.
Expert:  Chris (aka- Moose) replied 13 days ago.

Fuel pressure is good.

Long term trims should remain 20 to -20 and short term trims 10 to -10 You want to take these readings at a steady rpm, when you snap the throttle a change outside these parameters is to be expected.

Expert:  Chris (aka- Moose) replied 11 days ago.

Hello again Chris here,

  1. I have to assume you were not pleased with my help, because you have not replied or rated the post.
  2. What would you like to do regarding your question now?
  3. Do you still need help? Please reply I want you to get equal to or more than what you paid for.
  4. This post is coming up on the 7 day mark where it times out. That can prevent me from being able to post answers to your replies.

Thanks Chris

Customer: replied 11 days ago.
Sorry, work kept me away. Alright I always thought LTFT should be under 10 and anything above is out of normal range? So 20 is considered normal? Any ideas on what to check next? I'm at a complete loss here.
Expert:  Chris (aka- Moose) replied 11 days ago.

Do you still have lean codes stored?

What reading at hot idle do you get from the short term trims and MAF sensor?

Customer: replied 11 days ago.
still have the codes. Anything off idle LTFT go to 25 and do not come down. STFT 0-7 maf reads .7 (lb/m) at idle
Customer: replied 11 days ago.
Maf readings go up to 14.9 (lb/m) at wide open throttle.
Expert:  Chris (aka- Moose) replied 11 days ago.

The MAF min and max reading at hot idle is 4.8 to 6 G/S which is 0.63 to 0.79 LB/M

So your MAF is reading right.

Your STFT is within +/-10 at hot idle.

Your fuel pressure is good

If there were a vacuum leak, it would show up at idle when vacuum is highest.

I am beginning to think your PCM is to blame.

Customer: replied 11 days ago.
Any way I can test the pcm?
Expert:  Chris (aka- Moose) replied 11 days ago.

You have been doing the tests. Your finding that all readings show to be within specs though the PCM is showing codes that appear not related.

Customer: replied 11 days ago.
Could it be an injector or fuel pressure regulator problem?
Customer: replied 11 days ago.
I think the pcm may be the issue as well but want to explore all options
Expert:  Chris (aka- Moose) replied 11 days ago.

You already checked the fuel pressure so the regulator is out.

If it were a injector nit spraying enough fuel you should see the trims really high at set rpm as the computer is saying to add more fuel.

Customer: replied 9 days ago.
One more thing I forgot to mention. Every once and awhile I'd say twice or so a week the while coming to a stop idle will not come down to normal to the point where I'd have to hit the brakes harder than normal. I haven't pin pointed exactly how/when it happens bUT I'd say it happens after driving hwy for roughly 10 min. I notice it on my way to work. I did replace the iac valve early on bUT it never clearNed this issue up.
Customer: replied 9 days ago.
the plot thickens... I made some time this evening to pull the pcm to take a picture of the label for the part number and what not. Well I disconnected the battery, pulled the pcm, took a picture, hooked it back up had a smoke and decided to unhook the egr solenoid just to satisfy my own curiosity to have it unhooked then take a test drive and monitor data. I have a great 7 mile loop that is 25 mph, then 45, then 55 then 70 then back to 45 then back to 25 to the house. While taking this test drive the truck would not go into closed loop. A little after I got on the hwy the check engine light came on again. While I was monitoring data LTFM were fixed at 0 I'm thinking because of being stuck in closed loop correct? When I got off the HWY came to the 1st red light the engine was at roughy 1700 rpm and would not go down as I came to stop, I had to hit the brakes harder than normal to keep it from moving forward after a few seconds after I stopped it dropped down to normal idle with kind of a thud. I was able to repeat this concern every time I took that loop-did it 5 times. Now after the 1st loop I pulled over checked codes and now had po136 B1S2, P0156 B2S2, P0131 B1S1 and of course the P0171 and P0174, I then hooked that sensor back up and took the same test drive 5 times. I'm thinking that maybe the 02 sensor errors were just because the truck could not go into closed loop because that egr solenoid was not hooked up? I've graphed all the senors and used carb clean at idle to confirm they are reading correctly. Another very interesting this was at idle LTFTs were at 10-14 then normal driving they were at a constant 25. I did wide open throttle up to 80mph while getting on the hwy LTFTs went to down to 3-6 but shot right back up as soon as I drove normally with the cruise on and even at light to moderate throttle. Only at wide open did the they drop, I've never really monitored them like that before. Could there still be a vacuum leak somewhere or do you still think that it's pcm related?
Expert:  Chris (aka- Moose) replied 8 days ago.

I still believe this is PCM related.

Customer: replied 8 days ago.
Any thoughts as to what is causing that high rpm while coming to a stop? Or why my LTFT normalize at wide open throttle but read 25 off idle or light to moderate acceleration?
Expert:  Chris (aka- Moose) replied 8 days ago.

Trims will always go out of spec when applying or releasing throttle. Those PIDS are designed to be monitored only at a steady rpm. Unplug the IAC and see if the high idle is now gone.

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