1973 - 1979 F-100 & Larger F-Series TrucksDiscuss the Dentsides Ford Truck
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Hello, I got this truck two weeks ago and am having a problem getting air in the fuel system. So far, I have cleaned the fuel tank, replaced the sending unit, replaced the fuel line going to the pump, replaced the pump, and routed a new line from the pump to the carb. I have a clear inline fuel filter installed after the pump also. The truck runs great when it's cold, but once it gets hot, she starts developing large pockets of air in the filter. I've read where some people take off the filter to alleviate symptoms, but where is the air coming from? I have triple checked all my connections and hose also. Could air be sucked back through the carb somehow? Any suggestions? Thanks
Suggest you replace all rubber lines - every single one on the suction side - and add new clamps. The rubber cracks and can allow the pump to suck air or they get soft and collapse.
Some air or vapor is typical in the filter but running out of power when hot is NG. Also, how is your tank vent? Aftermarket caps like mine don't vent so well. As a diagnostic, maybe try running with cap loose.
I have already replaced all fuel hoses and replaced all the clamps, As far as the filter goes, it is made of glass and quite sturdy. I use the same filter on my other two vehicles with no problems. I have already tried running it with the gas cap off too, but I can always double check my findings. Thanks again
Is the air actually causing a problem? Carbed vehicles can deal with any amount of air in the lines as long as they still physically get enough fuel into the bowls. They dont require the fuel pressure for actually running the engine like some other fuel systems do.
If your filter is one of the kinds with two metal ends that screw together over the small glass vial, every single one of those I've had on a vehicle when I got it had been tightened to the point that the packings split and they leaked, either air in or fuel out. If you didnt put it on yourself, it may not be assembled properly.
It's not much work to check that out and remove it for testing.
Also, where is the glass filter, physically? They do a fantastic job of conducting heat to the volatile gasoline inside and causing it to evaporate faster than it should. Some times just fuel flow is enough to temper it and prevent it from boiling away, at least 'till you kill the engine or stop somewhere.
As an anecdote, my very first experience with vapor lock to the point that the engine would die was caused by one of these glass filters laying across the intake manifold and touching all of it's heat bearing goodness.
I folded my insurance and registration papers around it, wired it on with a coat hangar I found along the side of the road and continued on, making it from CA to KY before I remembered to pull it off and fix it.
What you don't mention is if this is affecting engine performance.
If yes then you probably need to find the source of the leak. It will be on the vacuum side of the pump.
If no then you need to install a metal filter so you can't see the air and worry about it.
65 F100 cc "Great White"
66 F100 shortbox "Blue"
91 Explorer work rig "The Dumpster"
77 F250 4x4 "Big Red"
Thanks for the pointers, you guys. I routed the new fuel line away from the major engine heat, and I this is actually causing issues with the engine. I can drive her around for 7 to 10 miles until she dies on me, then she wont get fuel till it cools down again. I did already take apart the filter as well and was questioning one of the gaskets on the inside, but I put it back together and it held pressure with me just blowing into it. I shall try removing the filter to see if the issue persists. Wish I could find some clear fuel line so I could visually tell if the problem continues though.
I had an issue with the short piece of hose that joins the metal lines,under the bed . Hose was cracked and sucking air . Never leaked fuel . Other than that ,If all rubber lines replaced, My guess would be vapor lock of faulty fuel pump .
78 F100 ,Daily driver . Life will test you . Never give up ....
I re-read your post and don't think you mentioned looking at the fuel tank or pickup. A gummed up tank or plugged filter sock on the fuel pickup could cause the problems you are having. The basic fuel system on these seems to do well even with today's gas so something is going on with yours. If lines, filter and pump are good that basically leaves the tank/pickup which is a pretty common problem with a 35 YO vehicle.
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