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Old 02-06-2011, 04:27 PM   #1
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Fuel Pressure Rapid Leak Down

During my last trip in January, I noticed hard engine starting. This seemed like a new issue since I never experienced any thing but instant start on first crank even after a long non use(days). Got home removed dog house and checked rail pressure. It was zero. Tried key-on-engine-off and observed pressure jump up to 62psi for as long as the pump primed. After pump prime finished, pressure quickly reduced to less then 30 psi in about 30 seconds. I suspected 3 possible causes:

1) Fuel injector leakage. Not likely-No engine malfunction or performance issues.
2) Fuel rail pressure regulator.
3) Fuel pump check valve leaking.
4) Internal fuel tank pressure line leakage.

I decided to test the fuel system by inserting air pressure. I chose the existing fuel filter location as the place to insert a known gauged air pressure, first l connected to the engine side of the fuel filter lines. The pressure held steady at 54 psi for as long as I wanted to wait. This indicated problems at the fuel tank. Not what I was hoping for.
In the same manner but connecting to the fuel pump end of the fuel filter lines. I sadly watched the pressure drop off as I had originally seen.

So, what does all this mean?
I seem to have the necessary fuel pressure when the engine is running and it seems normal enough on hill pulling. If there is a check valve that is supposed to prevent loss of pressure that is weak does it matter as long as the pressure and volume is there when its running?

Any body?

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Old 02-06-2011, 04:44 PM   #2
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Marty, as long as the fuel pressure is normal while the pump is running, I wouldn't worry too much about it. If the starting problem after setting bothers you, just cycle the ignition key a couple of times before engaging the starter. I think, not sure here, the check valve is built in to the pump in the tank.It may be just a speck of rust or or something in the check valve, and could possibly go away by its self in time. Would sure beat the alternative of pulling the fuel tank.

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Old 02-06-2011, 06:18 PM   #3
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Originally Posted by dieselclacker View Post
Marty, as long as the fuel pressure is normal while the pump is running, I wouldn't worry too much about it. If the starting problem after setting bothers you, just cycle the ignition key a couple of times before engaging the starter. I think, not sure here, the check valve is built in to the pump in the tank.It may be just a speck of rust or or something in the check valve, and could possibly go away by its self in time. Would sure beat the alternative of pulling the fuel tank.

Dieselclacker
Dieselclacker, Thanks. That is how I am proceeding.
When I did the test mentioned in the OP, I could hear air bubbling into the liquid in the fuel tank. Since I had a full tank at the time, I guess the air could have also been leaking in the line from the pump to the tank flange. I suppose I could repeat the same test when I have less then a half tank. If I still hear bubbling, I would assume leak is below liquid level and probably not in the pressure line leaving the pump.

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Old 02-08-2011, 07:57 PM   #4
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I new fuel pump will fix it.
Probably a rebuild would do it.
Its not an uncommon issue.
The biggest pain is dropping the tank.

I went through it, but was luckily in month 35 of my 3 year warrenty.
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Old 02-08-2011, 09:38 PM   #5
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I think it's the fuel pump also. Mine was changed under warranty and my previous MH, a Ford, I had to pay to have it changed. Neither one ever stranded me. As long as kept more than a 1/2 tank , I never had trouble but I felt I had a gremlin that was not going to fix itself.
But Dieselclacker may be right too, it's possible that whatever it is could pass.
If your engine does'nt want to start cold, I have no experience with that. Mine did'nt want to start when the pump got hot. I'd fill it with cool gas and it was good as new, for awhile.
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Old 02-08-2011, 09:54 PM   #6
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If your engine doesn't want to start cold, I have no experience with that. Mine didn't want to start when the pump got hot. I'd fill it with cool gas and it was good as new, for awhile.
Max, I had 3 fuel pumps replaced in my Ford vehicles with the same symptom. The last pump I got fixed the problem since it lasted for the remainder of my ownership. (about 2 more years)

I am not afraid to run my gas down to less than 5 gallons remaining in the tank. However my wife will be asking me to stop and fill up the rig as often as she blinks. So I try not to go lower than 1/4 tank.
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Old 02-08-2011, 10:26 PM   #7
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That's funny Driver, We are just the opposite. I just don't like to have less than 1/2 a tank. (Probably because it cost me $800 to replce the Ford MH fuel pump and warranty took care of my present RV fuel pump replacement.
I always tell my wife to keep at least a 1/2 tank. But then, I go to use her car , I find the "Low Fuel" light is often on.
She's got me trained now, I take her car and gas it up once a week.

Heck, I can't stand to have the MH parked with any thing less than a full tank, even if I don't plan to go any where.
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Old 02-08-2011, 10:54 PM   #8
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Heck, I can't stand to have the MH parked with any thing less than a full tank, even if I don't plan to go any where.
Since we have used our rig as a life boat when we have lost power here during a storm, I always park my MH with as close to a full fuel tank as possible. Also want to be up on LP but that lasts a while.
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