Hi from the UK
I have a 1994 ex US Air force F350 4x4 with a 7.3 IDI, sufddenly getting air into the fuel and I can't find out how it's getting there, the truck has only done 73000 miles from new, all the fuel lines are still shiny metal with all the original stickers on them, right back to the tanks so rusty fuel lines isn't an option, the Fuel pump went bad a while back so that has been replaced with a holley red electric fuel pump, I've just replaced that with a new Facet electric pump, I've replaced all the rubber lines up front and the Fuel filter and still there is air, it's draining the fuel filter in around a hour or so, I've closely inspected the fuel line front to rear and it's all bone dry, now at a loss

 

where did you place the e-pump?

 

I placed the electric pump up front on the chassis rail right next to the mechanical pump, had an electric pump in the same position for a couple of years now with no problems up until now

 

I bet it is the olives, Motorcraft PN: 9k260 & 9c387 (2 of each). There are 4 total on the fuel system and they are easily overlooked, One is on the fitting going into the front of the filter head, one on the fitting on the back of the filter head going ti the injection pump, one on the line going into back of the injection pump and one on the back of the engine where the return lines meet up. also there are 2 o rings in the filter head that seal the fuel heater plug, not sure on the sizes on those sorry. I think most guys suggest putting the E-pump back closer to the tank.

 

Hi IDIGuy
Forgot to mention i upgraded the fuel filter and housing as soon as i bought the Truck, them stock filters are impossible to get in the UK, I just put a temporary clear see through filter in the fuel line just before the electric pump, i see very small air bubbles coming up stream with the motor off, must be something further back then

 

Sometimes the feed hose can break off in the tank.

 

I don't think it's the feed in the tank that's broken as it's the same problem on either tank, wondering if it's the switch that changes tanks

 

The only other spot I can think of is the 2 o-rings in the quick disconnect on the fuel selector valve I think the feed line has the black lock clips and the return line has white clips

 

this morning the filter were empty, leak must be getting worse I replaced all 6 O rings in the fuel selector valve this morning, what a pita that was, left the truck running 20 mins and I see bubbles in the filter again, getting really hacked off now, thought my old chevy was unreliable but this is as bad

 

Bypassed the tank selector valve tonight and bubble bubble bubble aarrggghhhh

 

 

ah crap.yup that's no good.well unfortunately no one here can really tell ya just where its leaking.it's going over the system from that filter to the tanks.could be the pickup tubes at the tank are rusty and have pin holes there.the plastic/nylon fuel lines r their fittings to the selector valve,the connections out of the valve or the line to the filter.
the only tips that might help ya out,is the soapy water may help.might get lucky and see it pushing the air out of the lines if you wet them.may not be as easy with a high pressure tire for example but it's a start.beats trying to find a pin hole on a dry line.you'd never see it.
another tip that might be helpful is a common place for failure would be the supply line from the selector valve where its mounted in the metal clips.pull them out from the clips and put the water to them there.might find rusted pin holes.it doesn't take much.your looking for something so small you'd likely never see it without close inspection and wetting the lines.best of luck.

with the f250 and being a 4wd.the underside was a bit rusty looking of course (much more so than the f450 2wd truck which didn't get used on winter roads)
i didn't even bother with it brother.i just knew those factory 15+ yr old metal lines if not leaky yet,would be soon anyway.i just ripped them out before even putting the truck on the road and replaced them with fuel hose.

the metal fuel lines and the brake lines all got replaced right then as preventive.
for he f450 (same age truck.even 3 yrs older when purchased) they all look great.just no need to replace either system.iv no doubt just by looking at those,it would be needlessly tossing $ away as im sure they're "probably" be fine for 5-10 more years.with the f250's....not a chance.far too spotty looking.

 

Now i've replaced the line from front to just after the selector switch, that's almost to the tank now and still fuels leaking back to the tank, left it stood 2 days and the filters are dry

 

today I moved the electric pump to the chassis rail next to the front fuel tank, added a one way valve just after the pump and all was well for a couple of hours then the bubbles started again

 

so right after the fuel tank selector valve.what happens if you keep the pump here for now,and switch tanks? if it runs ok right here on the other tank for example,then you narrowed it down to the pickup tube or the nylon line in the one tank it bubbles on.if it does the same thing,then it's likely the fuel tank selector is the issue because whats the odds of having both tanks pickups tubes with rusted pinholes right?
keep at 'er.