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1987 - 1996 F150 & Larger F-Series Trucks 1987 - 1996 Ford F-150, F-250, F-350 and larger pickups - including the 1997 heavy-duty F250/F350+ trucks

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  #1  
Old 02-19-2014, 07:33 PM
digicon digicon is offline
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1996 F250 5.8 fuel pressure issue

Guys,

I have a 96 F250 4WD 5.8 that I have just owned for about a month. The truck had 130,000 miles on it and has been very well maintained and cared for by the previous owner. However the truck idles and runs fine but has no WOT power. Up until now I had only ran off of the Front fuel tank I suspected a fuel problem so filled the back tank and it was noticeably better.

Just so I wasn't imagining things, I bought a fuel pressure gauge and this is what I found.

Front Tank: (No Power at WOT)
1) 33psi running.
2) At Wide open Throttle fuel pressure goes to 23psi
3) I can cycle switch 3 times to a max of 23psi.
4) Pressure bleeds back over the course of a few minutes to 0psi
5) Fuel pressure acts no different if vacuum is connected or not to FPR.

Rear Tank: (Noticeably More Power at WOT)
1) 43psi running.
2) At Wide open Throttle fuel pressure goes to 33psi
3) I can cycle switch 3 times to a max of 33psi.
4) Pressure bleeds back over the course of a few minutes to 0psi
5) Fuel pressure acts no different if vacuum is connected or not to FPR.

It appears my front pump is weak. Should they both DECREASE fuel pressure when given a WOT cycle? Any input would be greatly appreciated.

Thanks,
Mike
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  #2  
Old 02-19-2014, 07:55 PM
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One other thing. I momentarily had the CEL come on last week. I read the code and it was a 172 (lean condition). The light came on for a while then was gone. All of this while running on the front tank. Keep in mind, I have only ran 3 tanks of fuel through this truck since I have owned it in 2 months. All through the front tank.
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Old 02-19-2014, 07:57 PM
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Originally Posted by digicon View Post
Guys,

I have a 96 F250 4WD 5.8 that I have just owned for about a month. The truck had 130,000 miles on it and has been very well maintained and cared for by the previous owner. However the truck idles and runs fine but has no WOT power. Up until now I had only ran off of the Front fuel tank I suspected a fuel problem so filled the back tank and it was noticeably better.

Just so I wasn't imagining things, I bought a fuel pressure gauge and this is what I found.

Front Tank: (No Power at WOT)
1) 33psi running.
2) At Wide open Throttle fuel pressure goes to 23psi
3) I can cycle switch 3 times to a max of 23psi.
4) Pressure bleeds back over the course of a few minutes to 0psi
5) Fuel pressure acts no different if vacuum is connected or not to FPR.

Rear Tank: (Noticeably More Power at WOT)
1) 43psi running.
2) At Wide open Throttle fuel pressure goes to 33psi
3) I can cycle switch 3 times to a max of 33psi.
4) Pressure bleeds back over the course of a few minutes to 0psi
5) Fuel pressure acts no different if vacuum is connected or not to FPR.

It appears my front pump is weak. Should they both DECREASE fuel pressure when given a WOT cycle? Any input would be greatly appreciated.

Thanks,
Mike
The lower the vacuum signal is the HIGER the fuel pressure should be. Lower vacuum equals more throttle/load therefore more fuel is required.

BTW....43 PSI at idle is way too high.......
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Old 02-19-2014, 08:09 PM
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Conanski Conanski is offline
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There should not be a drop in fuel pressure at WOT, in this case it should increase from 32-35psi at idle to the 40-45psi range under load. Is the vacuum line attached to the pressure regulator? It should be. Fuel pressure should not bleed off any visible amount over a short period of time either so you have 2 problems.. weak pump in the front tank and a possible fuel transfer problem(pressure bleeding off to the other tank) or leaking injectors.
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Old 02-19-2014, 08:16 PM
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It is attached. And both tank pressures decrease under WOT about 10psi accordingly. I don't see any difference when idling, as it pertains to fuel pressure, whether the FPR vacuum line is connected or not.......and there is definitely vacuum at the line. I can feel it.
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Old 02-19-2014, 08:24 PM
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Start by replacing the fuel pressure regulator/
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Old 02-21-2014, 08:09 PM
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digicon how are you making out. I'm chasing a similar problem?
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Old 02-21-2014, 10:34 PM
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I went out tonight and put a gauge on it again. Pressure from both tank (though different PSI reading) act exactly the same. Both decrease with throttle and bleed off after shut down. And act no differently weather the vacuum is supplied or not.

So....I took the FPR off. Beat it around, applied some vacuum, cleaned it off etc. Reinstalled and for once it held pressure after shutting of the truck. At least that was different. It still decreased pressure upon throttle but I did change one aspect of it.

So....I am thinking it is bad. I plan on replacing it this week. Possibly tomorrow. I'll post the findings.

What are your symptoms?

Mike
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Old 02-22-2014, 01:27 AM
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Similar as yours codes are 172 and ocasonaly 173. I put a gauge on it and had 30 psi running and 40 off. no change when disconnect of vac and it would jump and settle down on throttle. I started to poor out so I went in. Ill get back at in the am
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Old 02-22-2014, 08:40 AM
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Similar as yours codes are 172 and ocasonaly 173. I put a gauge on it and had 30 psi running and 40 off. no change when disconnect of vac and it would jump and settle down on throttle. I started to poor out so I went in. Ill get back at in the am
If you have "30 psi running and 40 off" then the FPR is working and the vacuum is dropping it to 30 psi at idle.
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Old 02-22-2014, 09:58 AM
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Haven't seen it mentioned, but has the fuel filter been changed? I had a similar problem, and just changing the filter made a big difference.
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Old 02-22-2014, 04:26 PM
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For what it is worth. I just replaced the FPR and hooked up the gauges. Every problem is fixed. Fuel at idle settles at 30psi from both tanks now. Fuel pressure INCREASES upon throttle from both tanks and best of all fuel pressure does not bleed.....actually bumps up about 2 psi upon shut off and holds steady.

All I did was replace the fuel pressure regulator.

Hope this helps you guys

Mike
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Old 02-22-2014, 04:30 PM
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Timbersteel, Good Point I should have mentioned. The first thing I did was crawl under the truck and noticed it had a brand new fuel filter. Actually the people I bought it from just replaced fuel filter, plugs, rotor, cap, wires, etc. Probably trying to fix this problem. $40.00 later.....I think it is fixed
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Old 02-22-2014, 04:30 PM
 
 
 
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