I have been fighting with My daughters 1991 f-350 7.3 liter diesel. My other threads are on here. Now I feel like I have my glow plug issues fixed. My problem Now is I can't keep fuel in the filter. I primed it last night (it has an e pump) I pulled the filter tonight and it only had about an inch in the bottom. Where or how can this fuel be siphon off? I find no wet spots. I just did replace the return lines and o-rings. Please I need some help this is about to drive me nuts. I am very good on gas engines and don't play much with diesels so this has me guessing. Is there some sort of check valve in the filter or filter head?

 

leaking injector? Or your fuel shutoff solenoid might be leaving the injection pump open or something, thats confusing to me. Your return lines are new, you might have a problem inside the injectors or something, thats my guess cause i have never heard of that.

 

Did you lube the O-rings? Also did you use Viton O-rings? Once you set the cap down, did you make sure it didn't move at all once set? If air gets in the lines, The fuel in the filter with settle. And air can definitely get in without any fuel getting out. So check you fuel lines and make sure you did a perfect job on them, If not, order some viton #111 o-rings, lube them and order some good quality return lines. Then what I found best to do is place (not push completely down yet) the caps on the injectors then attach all the fuel lines and secure with clamps. Then carefully push the caps on with the fuel lines already connected so when you push the cap onto the o-ring, you wont have to move the caps at all once its set. I repeat, if you move or rotate the cap at all once properly set on the o-rings, air will get in and give you problems like you currently have. Also, If you got your return line kit from pensacola diesel, thats also a problem.

Aune, If and injector was stuck open or what not, there would be a knock inside the engine that he would be telling us about.

 

X2, some motor oil on the o-rings helps out a lot! If not, it's a tight fit and you run the risk of tearing the o-ring when you slip the cap on.
I also hook up the lines to the caps and get them on the injectors, ten give each the final push when they're all hooked up. I also found a deep-well socket to work well with a very slight tap of the hammer to set the caps down. I don't remember the size, but I use the smallest size that will fit over the injector.

If your fuel is leaving your filter, then it sounds like the system is open...meaning the fuel is draining back to the tank. Air intrusion is the common term. Usually the return lines are the issue. But I would check the fuel supply and return lines that run from the tank up the engine. Over the years, the vibration of the fastening clamps on the frame can wreak havok on the fuel lines and leave little pin holes. Also check the schrader valve, it's the tire valve thing...maybe it's a little loose?

I don't know about the 7.3 filter heads, but they've got more "stuff" on them than my 6.9 filter heads...do the 7.3's have a check valve?

 

Back in the fuel tank.

The fuel system on the engine is all above the fuel level in the tanks.

So it is just like when you put a straw down in a glass of water, put your finger over the straw and raise it up.
As long as the straw has your finger over the end, the water stays in the straw.
Move your finger, water returns to the lowest possible level.

So on the fuel system, any leaks letting air in, let the fuel return to the lowest possible level, the fuel tanks.

An air molecule is tiny compared to a fuel molecule, so it is very possible for air to get into places fuel can not get out of.
That also makes finding air leaks in the return system one of the most frustrating jobs on an IDI engine.

Anyone you ask will tell you ro replace all of the O rings at once.
Then make a very consious effort to not disturb the lines once they are installed.
It don't take much hot fuel going through the return lines to make the new O rings hard enough that they will not reseal if they are disturbed.

When you install the O rings, coat the injector O ring area with motor oil, and the injector O rings.
Then roll the top O ring in place.
Now you can roll the lower O ring right over the upper one to get to the lower groove.

The slightest nick in the O ring in the wrong place, the O ring will not seal.

Another place that is rather famous for leaking air on the 7.3 style fuel filter header is the fuel heater connection on top of the header.

There are a couple O rings that seal that connection as well.

 

I did replace the return system since it had obvious issues. I did use a Pensacola kit may be a bad thing ??? I had no issue coated all the orings with oil and installed and connected the new hoses. I see no wet spots from the injectors now. The fuel heater was leaking from the connection I did replace the orings I used green o-rings for air conditioning since that is what I had that where the right size. I see no leaks from there now. Does the filter on the fuel head have a anti-drain back feature like oil filters have? I mean when I check the filter it is way below the center pickup tube. I would think the siphon would break as soon as tht fuel level goes below that pickup tube unless the anti-drain back is not working sucking it back to the tank.

 

I had problems with the Pensacola o-rings, they had a lot of flashing, I use Viton O-Rings - McMaster-Carr Item 9464K24 and Vaseline.

No wet spots does not mean no leaks ... Air is smaller then diesel therefore can leak air and not fuel.

I don't get the concern about air intrusion, you have an electric pump ... let the pump run for a few seconds and poof a full system!

-Enjoy
fh : )_~

 

yeah.you don't really care if fuel drains back or not with an electric pump.let it.all your concerned with is fuel leaks really.
the e-pump will purge all the air right on through to the tank.
you may be leaking at the Schedar valve though.there's a check ball in there that you can clean out too.sometimes they get plugged up and don't hold the fuel.a good cleaning usually does the trick.

 

It lives. Replaced the fuel supply lines from the tank to the e pump let the e pump prime system. It acted a whole lot different this time it turned over few times as soon as the injectors got fuel it fired off and settled down an ran good. Thanks to all for your help.