Ford 7700 fuel issues again

jhwis

Member
I recently replaced the fuel line from the lower tank to where it splits into three directions just below top tank. Line was leaking... Anyway tractor runs doggy. Ran it a few hours and it didn't improve. I've been having issues all summer. I suspect the lift pump isn't working properly as it doesn't seem to have much tension when I hand prime it. My question is with both tanks full of fuel, (gravity) should that put enough fuel pressure on it so the lift pump shouldn't matter or is the culprit still possibly the lift pump? I don't see any other leaks. This is frustrating.
 
If the screen in the bottom tank is plugged, you could hook up a Hoover vacuum cleaner to the tank and you still wouldn't be able to move enough fuel to keep the engine going under load.
 
I will take a stab at this one. You speak about a lift pump, so I will assume you have the Simms inline pump. The simms pump will run off of gravity feed from the fuel tank when full. Running and running right are two different things. The poppet valves inside the lift pump can get junk in them and not work right, or water in them and freeze in the winter. This causes them to pop out oF place and render them useless. Pull the fuel line from the filter at the lift pump. Put your thumb over the port where you pulled the fuel line off of. Pump the manual handle and it should suck your thumb in and hold it there. If not you have a lift pump problem. Take off the little bolt in the center of the lift pump and clean out the poppets and sometimes there is a small screen there. I just hit them with a fresh can of starting juice. Simms pumps sometimes get tired and need the gov. Assembly changed. This depends on if they had oil or not. Not sure I ever seen one wear out that had oil. Always worn from no oil, or water. If you have the CAV pump please excuse me and let me know And I can help you trake this problem down. Good luck Al
 
Was the oil changed in the pump lately? If you pump the lever on the lift pump fast while running and it improves it may mean the lift pump is weak.
 
Open the filter head bleeder and pump the primer.... if it shoots fuel 3' then it's probably ok... if it doesn't... take the line off the bottom of the pump and blow it back to the tank with small bursts of compressed air and see if that helps. If it does you likely have a blocked pickup in the tank. If not... I'd probably change the lift pump.

Rod
 
It is a CAV pump. I am going to change the lift pump as it isn't that expensive. If that doesn't help, I'll try the pickup in the lower tank. Also, I have thought about bypassing the bottom tank altogether and just using the upper tank (gravity).
Thanks. I'll let you know what I figure out...hopefully by next weekend.
 
Ok.... now I think you seriously need to clarify what you have exactly! A 7700 should have an inline Simms/Minimec pump with 4 lines coming from the top of the pump, inline... and a transfer pump mounted on the side of the injector pump body. It is possible that the tractor could have a replacement BSD engine that could be equipped with a rotary CAV model DPS rotary distributor pump. This will have 4 lines coming from the end plate of the pump head. If this is what you have.... then you will absolutely need another electric lift pump to supply fuel from the lower tank to the injection pump.
I would not go and eliminate the bottom tank. That will be more work replumbing than it would require to just fix the problem you have.

Rod
 
Rod, you are probably right. I am pretty sure it is all original equipment. I haven't looked close enough at the injection pump to tell you for sure. I am new to this tractor as my other main tractor is an Oliver. One way or another it isn't getting the proper fuel pressure. It is either the lift pump, getting air somewhere or plugged screen in tank like you suggested. This summer it ran pretty good except when I ran it down to the lower tank. That's why i suspect the lift pump. (Changed fuel filters twice...)I'm gonna start with switching out the lift pump. I'll keep you posted. Thanks for the help.

jh
 
One other item.... if it has a simms/minimec pump... and it's losing prime when it's sitting... you probably have leaking seals on the line from the filter head to the back of the pump. Those have a quad ring on each end of the line that degrades over time. However, once you get it primed up and running that should not effect performance much (if at all) while running.... until you shut it down and leave it for a bit... then it loses prime again.

Rod
 
Ok. It starts up great every time. It just loses power under load.
Seems to be often now. Was sporadic before.

jh
 
Perhaps some of them do have that on the cover, or have that in addition to Simms or Minimec. Without looking I can't say... I just know mine has Minimec very clearly on the side cover.

Rod
 
I'll have to take a look at one myself, but the more I think about it, the more I believe the cover says "CAV Minimec". I haven't seen "Simms" on a cover since the mid 60's.
 
Found this today in my pile of pumps. It came off of a 7600.
a239381.jpg
 
HAhaha. Call this one a DRAW I guess.

What's the extra bolt for on the side plate? Never saw that one before..

Rod
 
I think it's a secondary fill port. This would be needed for those engines used in England that had the aneroid valve fitted, since the aneroid went over the hole we normally use to fill the pump with.

Did you find the "CAV" on your pump?
 
Interesting.

To be honest, I spent a couple hours with the old warden today doing some baling but I never looked at the pump. I suspect it will look the same as the one in your picture save the extra fill port.

Rod
 
I looked at the pump today. It's the same as the one you pictured save the extra plug. I never really paid much attention to the lower part of the cover plate before largely because it's mostly obscured by the throttle cable boot on the 7710's.

Rod
 

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