Air at Fuel Filter Restriction Switch - Ford Powerstroke Diesel Forum
 
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post #1 of 3 Old 09-12-2019, 07:10 PM Thread Starter
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Air at Fuel Filter Restriction Switch

My stock 1997 F-250 SBCC 4x4 7.3 263,000 miles developed an issue that I have not been able to find by searching for trucks with a similar issue.

Background:
7 years ago I replaced the Fuel Filter Restriction Switch on the fuel bowl (it was leaking) with a 5-7 lbs oil pressure idiot light switch as I did not wish to just plug it. After this mod the light worked as it should. Fuel pump was replaced last year due to weep hole leaking. I do not have any fuel leaks. There has been no changes to the way the truck runs or starts, which is good.

The Issue:
The Fuel Filter Restriction light started to flicker on (as I accelerated) and off (when not accelerating) as I was driving in town the other day. When I got home a changed the fuel filter. It was clean and only had 2000 miles on it. Afterwards the truck started right up, but the Fuel Filter light now stayed on all the time. I drove it a couple miles to make sure the air was out of the filter bowl and such, light stayed on. Figured the idiot light switch I was using as a Fuel Filter Restriction switch may have gone bad after 7 years and proceeded to replace it. When I removed the switch no fuel came out of the hole. I replaced the switch and the light still stays on all the time. The truck still runs fine. I have no codes.

What seems obvious to me:
1. If there is air behind a 5-7 lbs, normally closed, pressure switch the light will stay on.
2. This is probably not a fuel pump issue as the bowl is after the pump low side and although the pressure could drop to zero if the low side of the pump was bad, there should not be vacuum to suck in air.
3. The air most likely entered the system via the fuel filter change and now can not escape as it should. as there is probably a restriction affecting this point.
4. I need to check the high side fuel pressure to make sure I am good there.
5. I think I need to check for restrictions in the fuel return

The questions:
1. Will a clogged screen in the FPR return to the fuel bowl cause this issue?
How do you get the FPR away from the fuel bowl to get the screen cartridge out with that
pressed in steel line going from the FPR to the bowl?
2. Will a restricted fuel selector valve/switch cause this issue? ( yes I have one on a '97)
I don't expect the tank screens at this point as I think this may be a return restriction.
3. I was going to pull the rubber fuel lines that run from the fuel selector switch to the metal lines on the frame rail below the cab going forward to the engine, at the metal lines and attach fuel and return lines going into a five gallon jug of diesel to determine if the restriction, if there is one, is forward of this point or in the selector switch / fuel tanks. Is this the best point to tap into the lines?
4. Has anyone else had a similar problem, what did you do to fix it?

Since in my mind this issue could be a symptom of a problem anywhere from the pump to the tanks I though it best to get some advice and suggestions before I start pulling thing apart and throwing money at it.
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post #2 of 3 Old 09-13-2019, 02:10 PM
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Is the truck running good? If so I wouldn't sweat it. Too difficult to diagnose when you're not using the correct sensor in the first place.

FWIW I removed the WIF and FRS from my fuel bowl about 150k miles ago and never had an issue...just change the fuel filter on schedule and motor on.
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post #3 of 3 Old 09-15-2019, 11:02 PM Thread Starter
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greenskeeper looks like you are right. The truck is still starting fast and running good.
After looking at some photos of the dissembled FPR it appears the the area behind that sensor is only fed pressure through a small orifice under the 'other' FPR screen above where the hard line meets the FPR on the '96-97 fuel bowl. A blockage there would fit the symptoms, and not be a problem.

Last edited by NotThatGuy; 09-15-2019 at 11:11 PM. Reason: fix
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