Hi folks. I need a diagram of the fuel supply for the engine on my 99.5 F-550. I am getting a slight injector knock on #8 and I want to see if I can rig up a small orifice (really small) fuel return at the opposite end of the cylinder heads from the fuel feed. I am thinking that a tiny orifice will be all that is necessary to bleed off the accumulated air in the passages next to #6 and #8 injectors. The fuel pump should be able to keep up with the extra volume if the oriface is small enough. But I want to check against a blueprint before I get started. Thanks in advance.

 

Are you wanting this bleed fuel to return to the tank or are you wanting to keep it a closed loop system and try to put it back in in front of the filter?

If you are planning on returning to the tank why not just put full flow return lines off both heads with an external regulator?

 

I was planning to bleed it off to the fuel return. I know that you can get the external regulated systems and that they are the best solution for the cackle problem that the PSD has. However I have come to learn that the main problem is simply air in the fuel in the passages on the heads. And the external systems are kind of expensive. I got to thinking that a small oriface at the opposite end of the passage from the fuel feed on the cylinder head would be good for letting the trapped bubbles out of the system. I don't plan on racing this thing, it's my tow rig, so I don't need a fire hydrant's worth of fuel like a closed circuit full flow regulated system would provide. So I was hoping to get a schematic of the fuel system complete with flows and design strategy to see if I could make this work. If the system is designed the way I think it is, it would be an elegant, inexpensive way to bleed off the trapped air in the fuel passages. I am hoping that the fuel volume supplied to the system is great enough to make up for the increased demand that the orifaces would bring and still maintain correct system pressure.
Here's a crude diagram that I drew out in MS Paint. I welcome any collaboration on this idea.

 

Looks like a cool idea, I'd play with it and maybe look into a patent. Let us all know what you figure out!

 

I also need some help from somebody who is good at calculating flow rates through an oriface. I flunked math in high school and never went back to math class because it wasn't required for graduation and I hated it anyway. What I need to know is how much fuel will flow through a given oriface at a given pressure. Or at least the equation to know how to figure it for myself. Thanks in advance.

 

Ok here is what I am looking for except for the 7.3. This one is for the 6.0. Anyone have a link?
http://dan.prxy.org/Truck/6L_bible_h.../Page_028.html

 

Here are some flowrate equations for water. I'm assuming that other liquids (fuel) would be fairly similar. I hope this helps.

D = .23 * sqrt(Q / sqrt(P))

Where

D = orifice diameter in inches
Q = flow in US gallons per minute
P = differential pressure across orifice

Solving for Q:

Q = (D/.23)^2 * sqrt(P)

note:
"sqrt()" denotes the square root of ()
"^2" denotes ()squared
"*" denotes "times"

 

Thank you for the reply TXstroker. I have a little homework ahead of me on this one.

 

I have the diagram you seek, if you'll send me your e-mail address I'll send it to you, but the diagram you drew is essentially accurate.

Out of curiousity, what has led you to the conclusion that air is making your injector knock?

I would think that if there were sufficient air in the system to make an injector knock that they would all be doing it, and in that case you would need the tank and pre-pump mods to remedy that, otherwise what ever little bit of entrained air that does get released to the rails shouldn't have any effect on the injectors operation as the air will rise to the highest point in the rail and the injectors are drawing fuel from the lowest point.

I don't want to discourage you from experimenting on it by any means, I love watching this kind of stuff unfold, but I think you are going to have problems maintaining sufficient fuel pressure. Ford already regulates the fuel pressure to the minimum as spec'd. by International, and I think bleeding more pressure off will create more driveability problems than it cures.

 

Good morning Cookie88.
Check your email for my address.
In response to your question about my injector knock, I am not convinced at all that air is causing my injector knock. However I have heard the cackle.wav files that several people have recorded and mine sounds exactly like that to a much lesser degree. And further reading on the subject has taught me that Ford's design for supplying fuel to the injectors is very poor. Why they didn't make a closed loop through the heads instead of just through the filter housing is beyond me. Reading on TexasTownCar's website about the experience he had and his solution gave me my current idea. I plan to do the tank mods whether my truck needs it or not because I feel that Ford's design is not "air tight". Pun intended.
And the main reason that I want to get a diagram is to see how the flow is laid out.
My thought is that I could bleed off just a small amount continuosly, small enough so that the fuel supply can make up for the extra volume and the trapped air that does make it into the cylinder heads have a place to go.
If this idea of mine won't work, oh well, I'll just go buy the full flow external regulated system that Diesel Innovations sells or something similar to that.
Injectors are very expensive and I want to protect them. This may be a nice inexpensive way to do it.

 

Did you get it? Sent it this morning.

 

Yes, I got it, I was at work all day and unable to reply until now. It is just what I was looking for. Thank you.
I hooked up my fuel injection pressure guage at the end of the day at work and found that I could get it to maintain operating pressure and bleed off quite a bit of fuel at the same time. I was unable to measure it as I couldn't get my fitting to completly seal up and there was a lot running down the side of the engine as well. Suffice it to say the fuel supply is enough to put in some orifaces. Now that was at idle and I would want to bleed off a lot less in the final design so there is adequit fuel supply at WOT. And while I was watching the fuel come out there was a LOT of air mixed in. It finally cleared out for a few seconds and then the air came back. It alternated from then on: clear, foam, clear, foam, clear, foam, changing back and forth every five seconds. So I need to drop the tank and fix the pickup and run a new fuel line from the outlet to the pump with clamps. Got to get rid of those o-ring connectors. Then when that is done I'll try out this design and I think that it will work as intended. My biggest challenge will be actually making the hardware to install. I don't have a machine shop at my disposal so I have to get creative. I'll keep you posted. Thank you again for the diagram.

 

Kwikordead, TXstroker01's calculation for water needs to be multiplied by .85 at the end (when you get the final answer) because Diesel Fuel has a Specific Gravity of .85. Most calculations are based on water (Specific Gravity of 1.0).

 

Kwikkordead, I've been looking at your setup and doing some research (I have the Ford Tech Service Info on CD-although it's for 2001-2002). I came across the part that states that the fuel pressure regulator sends all unneeded fuel (excess fuel under pressure above 75 to 80 psi[2001-2002, other years pressures may be different], back to the fuel tank through the return by bypassing the filter. Since the return is connected to the fuel filter assembly, it must make a "U" turn inside before going through the filter. What this seems to be (to me at least) is that after going through the filter assembly, all other fuel (the fuel in the rails of the heads) will be at a lower pressure because of the pressure loss across the fuel filter. Even the slightest drop in pressure will cause a return line from each head's fuel rail to stagnate (not flow) because of the slightly higher pressure of the fuel coming directly from the filter housing. (you're getting flow now as you're evaluating the problem because the fuel is only fighting atmospheric pressure- 0 psi). This is even before calculating pressure loss from use through the injectors and from piping configurations and restrictions. I know that it could probably be done, maybe with a small auxilliary fuel pump or something, but then there's the risk of disturbing the readings on the sensors within the heads, and from the diagrams and descriptions from Ford, these are substantial.

Any chance of finding the vacuum leak that's allowing the air into the system?

These are just my thoughts and with these and a dollar, you can get a cup of coffee in most places.

 

He already knows where the vacuum leaks are, that is what he was talking about when he referenced dropping the tank and running new fuel line to the pump. They are well known air intrusion sources on every PSD with an inline electric pump.

I would speculate that once he finishes the tank and pre-pump mods the bleed hole experiment will be just for fun as 99+% of his air problem will be gone.

No problem, let me know if you need anything else.