7700 fuel problem

jk dairy

New User
I changed the fuel filter on a 7700, now I can't get the thing to run. It'll start, but then it acts like it runs out of fuel. I've had problems with it sputtering when the top tank of fuel got empty, but when I fill it up it would run fine. There is about half a tank of fuel in the top tank now. Could the fuel lift pump be the problem? I replaced it before when the sputtering first started but it didn't seem to help that too much, it still sputtered. Anyway, now it won't run and I don't know what I should try first.
 
Did you bleed the fuel system after you changed the fuel filter? Do you have full flowout of the tank? If not, the tank strainer might be partially clogged.

Here"s a general method for bleeding a diesel fuel system.

Bleeding a Diesel Fuel System


Start at the fuel outlet of the tank (inlet to the filter). Shut the tank valve, remove the line at the filter inlet and holding a suitable container to catch the diesel fuel, open the valve. You should have a CONTINUOUS rush/flow of fuel out of the line. If it dribbles or is intermittent, check the fuel cap for a blockage of the fuel vent or the strainer upstream of the valve for clogging. The strainer/screen is attached to the shut-off valve, and is positioned up inside the tank. You will have to drain the tank and pull the valve to clean the screen.
If you have good fuel flow at that point, reconnect the line and open the bleeder screw at the top of the filter. Turn on the tank valve and wait till you have a steady flow of fuel with no bubbles at the top of the filter, then close the bleeder screw.
Your pump may have a bleeder screw. If so, open that until fuel streams out with no bubbles, then close it. If you cannot identify the bleeder screw, loosen the inlet connection at the pump and purge air at that point.
Go back and make sure ALL the fittings in the fuel delivery system are tight so they cannot suck air.
Make sure the battery is fully charged. Loosen the fuel fittings at the injectors, either one at a time or all at once. Crank the engine till you see all fuel at the injector fittings and then tighten the fittings. If you do indvidual fittings, the engine will usually start before you get to the last fitting.
Alternatively, you can "tow-start" it to save wear and tear on your starter. Leave the injector lines cracked open at the injectors at first to purge the lines. Then tighten them up and she should start.
Your injection pump puts out a very small amount of fuel (high pressure/low volume). BE PATIENT. If the lines are totally empty, it takes a lot of cranking to fill them up.
sixbales & Jerry/MT
 
Every 7700 I've seen has Dual Power, so they cannot be pullstarted. (unless this one is a straight 8-speed?)
Stumbling when it's running on the lower tank sounds like there's an air leak somewhere...maybe between the lift pump and the lower tank.
 
It may have an air leak between the lift pump and the tank... But that generally presents as a tractor that won't start without bleeding. This is more likely a plugged tank pckup. You can start by blowing compressed air back through the line.failing that you need to remove the tank and pull the pickup out and clean it.


Rod
 
Iirc there is no strainer on end of pickup tube. Just open ended. The fuel is pulled from top of tank. Fuel sender,suction tube,fill from upper tank in one assembly. I would check fuel pump for trash under round cover held on with one bolt in center.
 
From the factory, there is most definitely a screen on the pickup tube. If the last one you worked on did not have one, it was either pulled off, or it more likely fell off and is rattling around in the bottom tank.

The pickup tube HAS to go the bottom of the bottom tank, or else the tractor would run out of fuel when it's half full. The top tank only has a fill and vent line, that's it.

Best way to check for a plugged strainer is as follows: Fill both fuel tanks full. Pull off the line at the bottom of the lift pump. Fuel should flow freely in a nice stream. Anything other than a stream will require removing and cleaning the pickup tube strainer screen.
 
I think it's getting fuel,it flows out like you said it should and it blows black smoke,and seems to fire. Now it won't even start, when it would start it would die right away, like it ran out of fuel. I can't figure out what could be the problem, maybe a bad gasket when I changed the fuel filter? I'm stumped! Anyone have any other ideas to try?
 
I decided to change the fuel filter again and then she started right up and runs fine! Why, I have no idea, bad filter and or gaskets maybe? Any ideas? I guess it doesn't really mattter, she's running good now!
 
I've seen where gaskets were doubled up and the smaller one was installed along with a larger one, blocking fuel flow through the filter. This may be what happened.
 

I got two gaskets on my filters this last summer. It would start, make black smoke, then die, I got a new pick up pump and while putting it on, messed up the threads on the line into the pump so that it would suck air at that fitting and act the same.
 

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