Air in fuel lines
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New User
Joined: Oct 2007
Posts: 8
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Air in fuel lines
K, this truck sucks and/or I suck with diesels. New return lines are in, new fuel filter, would crank motor and press the stem on the filter to drain the air.? once I get only fuel coming out it will fire up. Drove it around for 10 minutes and shut her down for 10 minutes to address the loose oil filter and she wouldn't start again. Pressing on the stem on the fuel filter again and air came out again. What is the best way to bleed the system and to figure out the pressure and flow? Any ideas on what would allow air in the system again
? And with 192k miles is this diesel/ford thing really worth it? Again this is my first diesel and my first ford.
? And with 192k miles is this diesel/ford thing really worth it? Again this is my first diesel and my first ford.
Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 16
From: Nutter Fort, WV
Air intrusion can drive even experience diesel people crazy, so don't jump off a cliff.
Since the fuel tanks are the lowest part of the fuel system and the engine/fuel filter is the highest thing in the fuel system, and air leaking into the fuel system will let the fuel drain back to the tank.
Air molecules are much smaller than fuel molecules, so air will leak into places that will not leak fuel out.
That being said, for the fuel to drain back in 10 minutes says it is a rather large air leak.
In fact that should be big enough that it leaks fuel out of the system when it is running.
Possible checks,
Are you sure that all of the return tees are down?
Is there a possibility you cracked one of the return tees when you replaced the O rings and hoses?
Is the gasket seated properly on the fuel filter?
Is the fuel filter tight enough?
Are all the clamps on the return line tight and in the proper location?
Is the bottom section gasket in place?
Is the bottom section of the fuel filter on tight?
Is the water drain closed tight?
First check the fuel filter gasket, a little motor oil on the gasket when installing the filter helps keep it in place and makes it easier to get it tight.
Bleed the air out of the filter and get it started again.
Then look at every connection carefully looking for a fuel leak.
Now look under the truck.
Do you see any damp places on the fuel line back along the frame?
Several people have had air leaks at the clamps that hold the steel line to the frame from the line rusting.
How much fuel is in the tank?
The bottom section of the fuel pickup tube in the tank is a known problem for the 80's trucks.
After years of driving down the road with a non baffled tank, the bottom section breaks off and you run out of fuel with 1/4 to 1/3 tank showing on the guage.
Now the 90's trucks are getting to the age where we had problems with our 80's trucks.
On the fuel filter, remove the schrader valve (tire valve) and install a fuel pressure guage.
Unplug the back wire on the drivers side of the IP so the engine will not start.
Now have someone crank the engine for 10 seconds, you should have 4 to 6 PSI fuel pressure from the lift pump.
Now remove the fuel pressure guage and install a short hose over the valve stem and catch the fuel in a container.
Again have someone crank the engine for 10 seconds, you should have at least 1/3 pint of fuel in the container.
If the lift pump does not pass both the pressure and volume test, it needs to be replaced.
And a word of caution, if you need to change the lift pump and you get a replacement that has an almost straight arm, make sure you get the install instructions.
If it is installed improperly, either lift pump or possible engine damage will result.
At 192K miles you should have over 100K left in the engine.
Since the fuel tanks are the lowest part of the fuel system and the engine/fuel filter is the highest thing in the fuel system, and air leaking into the fuel system will let the fuel drain back to the tank.
Air molecules are much smaller than fuel molecules, so air will leak into places that will not leak fuel out.
That being said, for the fuel to drain back in 10 minutes says it is a rather large air leak.
In fact that should be big enough that it leaks fuel out of the system when it is running.
Possible checks,
Are you sure that all of the return tees are down?
Is there a possibility you cracked one of the return tees when you replaced the O rings and hoses?
Is the gasket seated properly on the fuel filter?
Is the fuel filter tight enough?
Are all the clamps on the return line tight and in the proper location?
Is the bottom section gasket in place?
Is the bottom section of the fuel filter on tight?
Is the water drain closed tight?
First check the fuel filter gasket, a little motor oil on the gasket when installing the filter helps keep it in place and makes it easier to get it tight.
Bleed the air out of the filter and get it started again.
Then look at every connection carefully looking for a fuel leak.
Now look under the truck.
Do you see any damp places on the fuel line back along the frame?
Several people have had air leaks at the clamps that hold the steel line to the frame from the line rusting.
How much fuel is in the tank?
The bottom section of the fuel pickup tube in the tank is a known problem for the 80's trucks.
After years of driving down the road with a non baffled tank, the bottom section breaks off and you run out of fuel with 1/4 to 1/3 tank showing on the guage.
Now the 90's trucks are getting to the age where we had problems with our 80's trucks.
On the fuel filter, remove the schrader valve (tire valve) and install a fuel pressure guage.
Unplug the back wire on the drivers side of the IP so the engine will not start.
Now have someone crank the engine for 10 seconds, you should have 4 to 6 PSI fuel pressure from the lift pump.
Now remove the fuel pressure guage and install a short hose over the valve stem and catch the fuel in a container.
Again have someone crank the engine for 10 seconds, you should have at least 1/3 pint of fuel in the container.
If the lift pump does not pass both the pressure and volume test, it needs to be replaced.
And a word of caution, if you need to change the lift pump and you get a replacement that has an almost straight arm, make sure you get the install instructions.
If it is installed improperly, either lift pump or possible engine damage will result.
At 192K miles you should have over 100K left in the engine.
Senior User
Joined: Apr 2006
Posts: 310
Likes: 0
From: maricopa az
Since my rear tank had rusted out prior to me owning the truck I only use the front tank I found my air intrusion coming from the tank selector switch sucking air from the rear fuel tank had quite a time figuring that one out.
