fuel line leak
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From: Indianapolis
fuel line leak
About 4 weeks ago I purchased at 89 F150. It had been sitting in a field for about 18 months. Field mice entered the engine compartment and chewed up a few of the wires in the wiring harness and some of the spark plug wires. Those problems have been solved. The fuel pump relay was bad and has been replaced. The throttle body was removed, cleaned up, and a new throttle position sensor installed. A new battery has been installed, a new fuel filter, new air filter and of course all new spark plug wires.
When the fuel pump starts either by turning the key or jumping the relay, I get 35-40 psi at the rail, but then a leak develops and the pump continues to run. The leak is in either the fuel supply between the filter and the rail or is in the return line. Both lines are "banded" together so I'll have to remove the banding to find the leak.
So, here is the question. I have already purchased a fuel pressure regulator anticipating that it would be bad after sitting with fuel for 18 months. Should I go ahead and replace that and then test the lines again, or should the leak be my first priority.
Additional background: 351W, 4X4, Auto, Regular Cab, Long bed.
Hunt4Fun
When the fuel pump starts either by turning the key or jumping the relay, I get 35-40 psi at the rail, but then a leak develops and the pump continues to run. The leak is in either the fuel supply between the filter and the rail or is in the return line. Both lines are "banded" together so I'll have to remove the banding to find the leak.
So, here is the question. I have already purchased a fuel pressure regulator anticipating that it would be bad after sitting with fuel for 18 months. Should I go ahead and replace that and then test the lines again, or should the leak be my first priority.
Additional background: 351W, 4X4, Auto, Regular Cab, Long bed.
Hunt4Fun
Cargo Master
Joined: Jun 2002
Posts: 2,033
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From: Aurora,Colorado
The O rings could be a source--but also check the fuel pressure regulator--even though the fuel pressure seems to be normal range--I think.
From your description--it would seem that you can't smell gas nor see gas leaking from any point on the truck--is that correct??
Pull off the vacuum line to the FPR and make sure that there isn't any fuel inside the vacuum line and inside the FPR vacuum line port.
I wouldn't replace the FPR before locating the leak--it is best to locate the original problem without making changes that could change or confuse the issue.If there is gas inside the vacuum part of the original FPR--then replace it.
You could also pull the new fuel pump relay when it is running and make sure that the fuel pump will stop after the relay is pulled.
If all of the above seems normal on your truck--try then replacing the FPR.
From your description--it would seem that you can't smell gas nor see gas leaking from any point on the truck--is that correct??
Pull off the vacuum line to the FPR and make sure that there isn't any fuel inside the vacuum line and inside the FPR vacuum line port.
I wouldn't replace the FPR before locating the leak--it is best to locate the original problem without making changes that could change or confuse the issue.If there is gas inside the vacuum part of the original FPR--then replace it.
You could also pull the new fuel pump relay when it is running and make sure that the fuel pump will stop after the relay is pulled.
If all of the above seems normal on your truck--try then replacing the FPR.
Last edited by phoneman91; Jul 22, 2007 at 06:41 AM.
Fleet Owner
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From: Easton,Ks
Sounds like you have two problems:
Bad "O" rings causing the leaks.
And a Bad EEC Computer causing the pumps to run for more than 1 second after the key is turned to the on position if the Fuel Relay is not jumped and the engine is not cranking or running.
Note a leak will not cause the pumps to run for more than one second after the key is turned on.
Bad "O" rings causing the leaks.
And a Bad EEC Computer causing the pumps to run for more than 1 second after the key is turned to the on position if the Fuel Relay is not jumped and the engine is not cranking or running.
Note a leak will not cause the pumps to run for more than one second after the key is turned on.
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Senior User
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From: Indianapolis
The fuel does leak where you can see it. The fuel drips off of the fuel line going down to the fuel filter.
Sounds like changing the O-rings is a place to start.
Thanks for the ideas. That will be the plan and then I'll post a follow-up.
Thankfully this is not going to be my daily driver so I don't have an urgent need to get it up and going. More later...............
Hunt4Fun
Sounds like changing the O-rings is a place to start.
Thanks for the ideas. That will be the plan and then I'll post a follow-up.
Thankfully this is not going to be my daily driver so I don't have an urgent need to get it up and going. More later...............
Hunt4Fun
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From: Indianapolis
Leaks are fixed and the fuel flows good up to the fuel pressure regulator. If I let the pump run a few seconds, it will leak at the end of the fuel line right before the regulator. But I get no pressure at all on the rail. I'm planning to change the regulator. Just started that this evening. Those bolts are a pain! Got one out, still working the other two.
Sound like I'm on the right track?
And the computer is working fine. The leaks were only occurring when I bypass the fuel pump relay to test the line. The lines and o-rings could be ok and I just pushed them too far by letting the pump run too long.
Checked the lines to the relay today and my son turned the key. Getting two volts with the key on, so the PCM is ok, correct?
Sounds like a clog of bad fuel someplace to me.
Can the fuel line be cleared with a little low pressure air on the rail? Haven't tried that, just thought of it.
Hunt4Fun
Sound like I'm on the right track?
And the computer is working fine. The leaks were only occurring when I bypass the fuel pump relay to test the line. The lines and o-rings could be ok and I just pushed them too far by letting the pump run too long.
Checked the lines to the relay today and my son turned the key. Getting two volts with the key on, so the PCM is ok, correct?
Sounds like a clog of bad fuel someplace to me.
Can the fuel line be cleared with a little low pressure air on the rail? Haven't tried that, just thought of it.
Hunt4Fun
Fleet Owner
Joined: Aug 2005
Posts: 23,668
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From: Easton,Ks
Originally Posted by Hunt4Fun
Checked the lines to the relay today and my son turned the key. Getting two volts with the key on, so the PCM is ok, correct?
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Senior User
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From: Indianapolis
Sorry, should have said wires on the fuel pump relay. It showed a voltage of 2 volts when the key was turned.
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From: Easton,Ks
Originally Posted by Hunt4Fun
Sorry, should have said wires on the fuel pump relay. It showed a voltage of 2 volts when the key was turned.
Fleet Owner
Joined: Aug 2005
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From: Easton,Ks
Originally Posted by Hunt4Fun
OK. What should the voltage be when the key is on for a second?
A Diagram of the 1989 F series fuel system.
Fleet Owner
Joined: Aug 2005
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From: Easton,Ks
Your email address does not work.
Here is my reply to your email.
It should never leak fuel, it is designed for the fuel pump(s) to run all
the time. The reason they only run for one second when you turn on the key
is for safety reasons and when the engine is running or cranking (over 300
RPM) the pump(s) will run all the time.
If they do not run when pin #6 is grounded then you either have a bad fuel pump relay, wiring under it or there is no power to the yellow wire on the fuel pump relay.
Also check the Inertia switch.
Here is my reply to your email.
It should never leak fuel, it is designed for the fuel pump(s) to run all
the time. The reason they only run for one second when you turn on the key
is for safety reasons and when the engine is running or cranking (over 300
RPM) the pump(s) will run all the time.
If they do not run when pin #6 is grounded then you either have a bad fuel pump relay, wiring under it or there is no power to the yellow wire on the fuel pump relay.
Also check the Inertia switch.
Last edited by subford; Aug 2, 2007 at 07:35 PM.
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