fuel return priming system...

drain valve on original equip filters can leak, cause hard starting overnight. 1 way to tell is remove filter after sits overnight, fuel level in filter will tell if you have drain back overnight. I have taken out schrader valve in filter base used vacum pump to determine if you have an air leak in system. have to isolate line to returns to do this. I also have an extra fuel cap with schrader valve threaded into it, about 5-7 pounds pressure here helps a lot with bleeding.

Those are some good ideas, steve. Thanks.

fuel heater o rings leaks are a common source of air leaks. I hope some of this helps get your truck started.

Good gawd man
Go proofread the wall o text PLEASE...

Clb said:

Good gawd man
Go proofread the wall o text PLEASE...

Click to expand...

Haha sorry , you should see my hand writing.... The wife likes to say ive got the handwriting of a Dr without the degree... God definitely did me no favors with the grammar either... Ill go back and spruce it up for those of you who cant read *******...

Thewespaul said:

https://classicdieseldesigns.com/collections/fuel-delivery/products/billet-3-8-check-valve

Click to expand...

You want this on the supply side between the pump and the tank right?

Do you typically plug the air bleed check valve/fitting on the filter head?

I always plug the return from the filter, the check valves I recommend to place in the soft line before the lift pump between the block and frame on the 7.3s, if it is going on a 6.9 with the water seperator still in use I put them in the soft line ahead of the separator below the level of the lift pump.

Has anyone heard of using o-rings on the fuel lines? I forgot if t was here or another forum i saw someone talking about using o-rings to help seal the lines.. ive noticed some light wetness around a few of them since ive swapped to the R&D rails. Also i just noticed while i was messing with it on my lunch theres a massive fuel leak somewhere on the back side of the motor has to be around that return line tee. I planning on running some new hose down and removing that fuel filter return line from my filter.wish me luck...

I don't think that these rails will actually seal without o-rings in place. Just like the plastic return caps.

olives, square cut neoprene rings are used to seal metal lines. idi tech part of forum is your friend.

nelstomlinson said:

I watched a Stanadyne video on our pumps, and now I am totally confused on how a leak in the return line causes trouble. Near as I could make out from the Stanadyne video, the fuel comes in from the supply line, and that's all there is to it. How would air in the return lines be a problem? Is it because the return lines are hooked to the fuel filter, so the pump sucks return air through the filter? Do the return lines HAVE to be hooked to the filter?

Edited to add: the problem is that the return line leak lets the supply side empty back into the tank, right? So removing the return line to fuel filter connection should help a lot. Can we do that?

Click to expand...

Most people have taken their straw at the restaurant, put it down in their drink, put their thumb over the end, and have pulled the straw out of the drink and watched the drink stay in the straw, hovering in place as long as they keep their thumb over the end of the straw.

That is how the fuel system in these trucks work. The fuel pump pumps the fuel from the tank up to the top of the engine, filling the filter, the injection pump and eventually the return system. When the engine is turned off, the fuel should stay or "hover" in the fuel system on the top of the engine. If the system is totally sealed at the top, the fuel will stay up there, just like if you have your thumb sealing the straw. Any little air leak will let the fuel start migrating back down the return line to the tank.

You can tell sometimes how bad the air leak is. If you stop the truck just for the night, and it stalls in the morning and takes a lot of cranking to get it going, you have a fairly large air leak somewhere. If you have a smaller leak, it will not take as much cranking. If you have a very small leak, it may have to sit a couple of days before it gives you trouble.

Don't forget about the heater on top of the fuel filter housing. If there is any wetness around that area, it is leaking and letting air in, it's a common problem area also for air intrusion. Look the fuel system over carefully after running the truck for a week or so, any wetness is a clue there is a air leak there.

franklin2 said:

The fuel pump pumps the fuel from the tank up to the top of the engine, filling the filter, the injection pump and eventually the return system. When the engine is turned off, the fuel should stay or "hover" in the fuel system on the top of the engine. If the system is totally sealed at the top, the fuel will stay up there, just like if you have your thumb sealing the straw. Any little air leak will let the fuel start migrating back down the return line to the tank.

Click to expand...

Franklin2, we don't really care about the fuel in the return lines, right? It's just the fuel in the supply side that has to stay in place?

not necessarily, the rubber line between fuel filter base and return line is the interconnection. this is why return line leaks will cause air in fuel. this is the point in plugging this line. a service bulletin came out from ford years ago to turn a loop in this line, purpose being an air lock, I have looked can no longer find this. I plug them as SOP. however a fuel pressure gauge placed in in return line can help to determine if you have an injector leaking down,by watching how long it takes to lose pressure. you also have to plug or pinch off return line at back of engine before it goes to tank. pinch off hose clamp pliers work well for this.

steve phillips said:

olives, square cut neoprene rings are used to seal metal lines. idi tech part of forum is your friend.

Click to expand...

where do they go? im pretty green here not sure where to even look on the forums... I searched a bit and didnt see anything about it.

nelstomlinson said:

Franklin2, we don't really care about the fuel in the return lines, right? It's just the fuel in the supply side that has to stay in place?

Click to expand...

Return lines are part of the complete fuel system on top of the engine. Air entering anywhere in this system will let the fuel start draining back to the tank. A leak in the return line over top of the bellhousing back there probably would not matter, but any leak on top of the engine is going to cause a problem.

I don't know all the ins and outs of the injection pump, but I believe it has a return line on it, and when the fuel leaks down in the return system, it will drain the injection pump. That is why when you have this problem, the engine will start and run and then stall shortly after. The engine runs on the fuel left in the high pressure injection lines, and then all the air from the injection pump hits and it stalls out.