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Tim Mohr
Tim Mohr, ASE MASTER TECH
Category: Ford
Satisfied Customers: 13303
Experience:  30 YRS EXPERIENCE, FOREIGN AND DOMESTIC, GAS AND DEISEL
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Hello i have a 2005 ford f 150 with a 5.4 triton it has been

Customer Question

Hello i have a 2005 ford f 150 with a 5.4 triton it has been idleing rough and i have been getting eratic fuel pressure i have replaced the fuel pressure regulator and the fuel pump and it still does this what else can it be
Submitted: 4 years ago.
Category: Ford
Expert:  Tim Mohr replied 4 years ago.
hi, my name is XXXXX XXXXX is the fuel pressure reading on this?
Customer: replied 4 years ago.
The fuel pressure is eratic to say the least,when the truck is cold it runs fine its when it runs awile you start to get a miss and major spike in fuel pressure followed by a major drop in pressure and the cycle repetes itself the pressure normally should be between 35 and 70.It spikes to 90 or so and drops as low as 2 -3 lbs i put a new fuel pump and pressure regulator,filter as well.I am thinking it may be in the fuse panel there is a fixed relay or possibly a computer issue.If you want you can give me a call @ XXXXXXXXXX my name is XXXXX XXXXX you
Expert:  Tim Mohr replied 4 years ago.

If the pressure is spiking it is not going to be electrical, it is going to be a bad regulator or a restriction after the regulator, since you have already tried a regulator, this leaves a restriction, possibly in the fuel pump hanger, did you replace the fuel pump only, or did you replace the entire module?

Customer: replied 4 years ago.
The whole module
Expert:  Tim Mohr replied 4 years ago.

were these symtoms there before you replaced the pump?

Customer: replied 4 years ago.
Yes but much worse
Expert:  Tim Mohr replied 4 years ago.
the fuel pressure was spiking with the old pump?
Customer: replied 4 years ago.
The pressure before the pump swap would not go above 20 psi after the change the pressure was normal beween 35 and 50 psi until the truck warms up and then gets eratic up and down
Expert:  Tim Mohr replied 4 years ago.
i suspect you originally had a bad pump, then you got a bad replacement, the only way you get a pump that spikes to over 90 psi is if its a bad pump or a restriction, or a bad regulator, where did you buy the punp?
Customer: replied 4 years ago.
I bought the pump from carquest and the pressure regulator from the ford dealer.I stay away from pumps from advance auto,i have had really good luck with my carquest supplier i buy 20 to 30 per year and have had little issues but i guess you never know.The pressure definatly spiked @ or damn near 90 psi its tough to tell when the guage is going crazy but pretty close.I have read several tsbs regarding these issues with these trucks and some point to either wiring,relay or computer issues i dont know,i figured i cant be the only person experiencing these issues; gotta love it
Expert:  Tim Mohr replied 4 years ago.
Carquest sells the airtex pumps, the same as advanced, i would try one from napa, but get the delphi pump we have had several problems with the airtex pumps,Tim
Customer: replied 4 years ago.
ok so you think i should replace the fuel pump fun this thing has a extended range tank so its huge,are you pretty sure this is it?
Customer: replied 4 years ago.
Do you think there can be anything on the truck burning the fuel pump out?
Expert:  Tim Mohr replied 4 years ago.
I think you have a defective pump, if it wasnt spiking before you replaced it, then it has to be a bad pump,I cant see anything else causing this,Tim
Customer: replied 4 years ago.
Well Tim it turns out the these fords have a fuelpump driver module located above the spare tire that is mounted to the truck frame.You must be a ford tech from the south because up north where i live in the salt and the snow these modules are the first thing these ford techs are looking at apparently the salt and ice eat through the aluminum housing causing this short circuit and the eratic issues i have been experiencing. The demand for these modules has been so great that ford has a factory back order on these modules til at least the beginning of april i was able to cross the number to an identical part with a slightly different mounting bracket and have it coming in tomorrow,i appreciate your attempt at solving this dilemma and maybe this will help you help others in the future cause it seems this is a major really commom issue
Expert:  Tim Mohr replied 4 years ago.
we have had problem with the module, but not with these symptoms, the module will cause a no pressure problem, but i have never seen them cause a high pressure problem, this would require more voltage, and it cant make more than 14 volts without the voltage regulator being bad, let me know what you find,Tim
Customer: replied 4 years ago.
Thank you i will keep you posted
Expert:  Tim Mohr replied 4 years ago.
I'll be here,Tim
Customer: replied 4 years ago.
Well today i shipped the truck and the driver module was the culprit.This is the first time i am using this site,and thought i might pay for a correct diagnosis and not some simple advice that a mechanic would know i own a shop and did the simple things you suggested before i approached and outside assistance.The impression i got from your profile (and im sure it is accurate) was that you are a expert ford tech but the module never was mentioned by you it was i who suggested the fix which is what it turned out to be.I guess this site is more for homeowners and not for mechanics seeking a quick fix or a suggestion of previous ones you might have come across because this seems to be the main fault the is occuring in these fords the part is on backorder from ford til the end of april and they are selling on ebay for more than double,everyone and their mother is chewing up a driver module somewhere.Good thing i had the know how to get a module for a f250 same module different mounting bracket and it was available the next day.Therefore i dont really believe i should have to pay 15 dollars for you to tell me my fuel pump is bad when it was not the pump is expensive enough 15 more dollars for inaccurate info just is not right to me.Good thing i did not drop that 7 foot long extended range 3/4 full fuel tank for nothing,sorry for taking your time and appreciate your effort
Expert:  Tim Mohr replied 4 years ago.
,

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Tim Mohr
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