Hi I just purchased a 1985 Ford f250 6.9. New to this site but it has answered many of my questions. I can not find help with this in the Archives. My truck will start and soon die than will not restart. I took filter off this morning and there is air inside as the fuel was low. I connected a clear fuel line from filter to first injector at bypass. I sucked fuel from filter side and it seemed to fill after a bit of air. I turn over Engine and Air bubbles along with fuel enter from filter side. If I continue to crank engine fuel from filter will run solid for a bit and than a burst of air bubbles than back to mostly solid... and again a blast of bubbles. If I stop turning over with some fuel in clear line I see bubbling that in time almost stops... occasional bubbles continue to enter. I do not see any fuel loss anywhere? Does this description narrow where I may be having a problem?

 

Most likely air intrusion from return line caps. Search this forum for air intrusion...

 

Thanks Phy, I have replaced all caps, O rings and return lines. I'm not sure on how system flows. I hooked clear line at return line where attached to fuel filter and to the line I pulled off. It seems fuel comes from filter toward return line jet. The air is definitely being carried with the fuel. Like I said fuel is sometime solid with sudden gush of tiny to small bubbles. Clears and then continues the same. The caps were all pushed down solid and I do not seem to have any fuel seepage. So, would this indicate the air is entering prior to filter or am I wrong on how it all circulates?

 

Is the fuel tank less than half full?

 

I do believe I am less than half full. Maybe between a third and half?

 

These Ford trucks have a history of suckin air at the fuel pickup in the tank once that get low on fuel. All of my trucks have had this issue, we now keep the fuel level above the half full level.

 

Tank Guy - I did watch a video where someone had hooked up a clear line to observe bubbles. His line came off the fuel filter on its own designated fuel line out the upper drivers side of filter housing ... and lead to 1st injector cap. My configuration is slightly different. It is teed off a line connected to rear of filter housing. Probably does not matter ... mine just an earlier version. He claimed that air getting into that line indicates O ring jet leakage along passenger side of engine? I do not know what direction he had bubbles running towards.... possible from injector end towards fuel filter? I have bubbles coming from fuel filter towards first Jet. So, I assume that to be air entering prior to filter unless it can route itself back to filter and towards jet by other means? It would make sense to me that its the tank... Except my last tank full had run down to 1/4 and I didn't notice a problem. It was also warmer outside. Also, I was not having this problem prior to changing out all the Jet O rings, caps and lines. I did buy aftermarket Kit? I also pulled up on the oem Water separator ring and nothing came out the bottom. I don't think engine was running. It was all very dry and maybe that system has been bypassed? There is a line entering and a line exiting out the bottom of water fuel separator. The line configuration seems a little confusing at a glance as to how it routes into separator. I'll have to examine more close and see if its bypassed. If not I assume I can remove the 2 lines from Separator and connect together?


This is assuming that I surely have a leak prior to Fuel filter. Winter is not my favorite time of year to be outside crawling around a truck. Would really like to narrow it down as much as possible. If in fact a fuel tank issue how difficult is it to solve the Problem? In the next week or two I'm supposed to drive 800 miles and usually don't stop for every half tank refill.

 

Exactly.

Taking pictures of your setup and posting them would help a lot.

also, just think in terms of the fuel. Follow the lines and look at potential sources of air. It's not magic; there's nothing special here -- fuel from the tank ends up at the low pressure transfer pump on the side of the block, which then makes it's way into the IP, which creates the high pressure to inject it. Excess fuel is returned to the tank through a second hose.
Filters are somewhere on the intake side of the IP; I don't know what's still there on yours and what's been bypassed

 

I had some replacement return line caps that were poorly made, and were almost impossible the get the hoses to seal. This let air in. The return lines and caps are touchy to get sealed, and you since you didn't have the problem before changing the o-rings...

 

Have you checked the plastic tee's on the return lines at the injectors to assure they are seated all the way on? I have found that a light tap with a broad screwdriver on top will drive them down another 1/8" or so.

 

If he's getting air /out/ of the filter, in a constant amount when cranking, it's not the return lines.
Even if the filter managed to leak 1/2 out, you would get a solid block of air out of the air, then spit for a few seconds and not have any more air in it.

 

I'm thinking the same Macrobb, Tiny Air bubbles come gushing, sometimes popping creating a large air pocket and may clear becoming solid fuel for a sec than another air bubble gush and continues as such as I'm cranking. Air comes out of the Fuel filter towards the injector via return line. ( I would think if caps or O rings let air in when not running would flow towards filter not the reverse. When cranking air in filter would flow out towards jets but would soon clear itself and be solid fuel, no more air until engine turned off. Likely, while running fuel would leak out of caps/ O rings.) So I guess since Macrobb seems to be correct on this I should work my way back towards fuel pump, fuel Water separator, lines and tank. My truck does have its original setup as I've seen other of the same era identical. There is an air relief valve on drivers side of filter housing. Rear of filter housing has a brass fitting with line out to injector pump with elbow which runs the line for return. So at the same point on the filter housing are two lines somewhat intersecting , one to injector pump and one for return line. My truck also has its original water separator. Not sure if bypassed but I do not see any other water separator from tank onward. Since I have read that the old separators can be a problem maybe that should be my focus. Can I just attach the lines together in and out of Separator if they are still connected at that point? Thanks! Do I really need a Separator? Can I get by temporarily without one?


When I have gotten it started It blows some grey/blue/white smoke for just a very short period than clears up. Even when driving I don't get any smoke. Certainly have not seen any black smoke at all. The engine sounds right and runs fine.

 

UpDate... warmer today and was able to get my Truck started up. When idling it did send a constant flow of air bubbles from filter to injector via return line. I gave it high RPMs and bubbles somewhat cleared off for a period than again a rush of bubbles. What I don't understand is why when at idle and at speed the engine seemed to run very good with tailpipe smoke clearing off within moments. If that much Air was entering why does it not seem to effect my idle and running. Could Air only be going towards the return and not to the Injector pump?

 

Air is lighter than fuel, so it will tend to rise to the top. It will preferentially go out the return line on the filter head, due to it being "up".
Once it gets into the IP, it will take the "upper" path through the vent wire assembly and out the return.

If there is /too much/ air, however, you will have problems.

 

Thanks Macrobb, I have a little better understanding of how it all seem to function. I did as you suggested and pulled the line off the fuel pump, connected an extension and placed in can of fuel. It cleared out most the air when idle. When I revved it up seemed less but some air bubbles came out of return line. I next went and pulled both lines off the Fuel separator and connected them together with a clear line. Started and ran truck. No bubbles at all in line bypassing fuel separator. Still some air in return fuel line. I decided to connect a clear line from fuel feed and the other end on the line I had placed in fuel can leading to pump. Ran engine and fuel line to pump had no air at all. Still getting some air in return line when bumping up my RPMs. Almost resigned to the fact that I needed a new fuel Pump. Decided to disconnect the rubber line on pump and connect a new rubber fuel line from Pump. I went to disconnect line and discovered a clamp was slightly loose. Now all connected with new line. All air seemed to clear off and no bubbles after a little run time. Next, I have yet to reconnect the lines to the fuel separator. Not sure still if it was the line I replaced going to fuel pump or the Separator that caused the air leak. Maybe both. Tomorrow I'll check to make sure no air entered after sitting overnight and reconnect the fuel separator lines to see if air returns?