Ford 755B losing power/rpms

Old boy

New User
I recently purchased a well used and poorly maintained Ford 755B Backhoe tractor. It was running fairly good but started running rough so I replaced the fuel filters, long past due. Afterwords I had trouble priming the filters and ended up replacing the feed hose from the tank and tightening some loose fittings. Now the tractor starts good but won't rev up. If I run the throttle up and pump the primer pump the engine will rev up but when I stop pumping it idles back down. I've redone every fitting checking for leaks, do you think I have a leak somewhere or is this a sign of a bad fuel pump. Diesel is not my specialty. It has a Lucas CAV pump and the only working gauge so far is oil pressure so I can't tell you rpm's.
 
Sound like your low pressure supply pump may be going bad. They are readily available, not too expensive, and easy to change.
 
ok thank you, I just have to find one. Would that be the same as the primer pump or perhaps a fuel transfer pump? so far those are the only pumps I can find for sale. I'm going to look up where that is located on the engine. Like I said, I'm new to diesel.
 
I've looked at the entire fuel system in the parts manual and cannot find any such pump, is it part of the main pump? Would it hurt to add a small electric fuel pump from the tank to the filters?
 
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can anyone tell me if the primer pump on this tractor has anything to do with maintaining fuel pressure to the pump or is it simply for priming. As far as I can tell it only operates when manually pumped and it does that just fine. I don't want to replace it for no good reason. It's goes before a Lucas CAV injector pump, I can find no other lift pump or a low pressure supply pump. I tried a small electric fuel pump from the tank up but it made no difference.
 

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That primer pump does not maintain pressure and is only for priming. Have you tried checking the fuel flow coming out of the tank? If that is partially plugged in the tank the primer pump may be creating enough suction to over come the blockage.
 
It looks like the parts are no longer available from New Holland. If Dieseltech chimes in perhaps he could offer some help. You had asked about using an electric fuel pump and that may work but I don't know what you would need for pressure and flow rate.
 
I found those three parts online for $116 + tax and shipping. I'm an old time auto mechanic, do yo think I should give it a try?
 
It looks like you only need to take the back off the pump so it is worth a try. Worst case you will need to remove the pump and send it out to be rebuilt.
 
Thanks mhb@ufe for the help, the pump parts you described where in good shape and working properly. The problem was in the end plate assembly that covered those parts, there's a small piston in there that was hung up and once I loosened it up the tractor came back to life. I would never have found it without your help, thanks again.
 
Thanks mhb@ufe for the help, the pump parts you described where in good shape and working properly. The problem was in the end plate assembly that covered those parts, there's a small piston in there that was hung up and once I loosened it up the tractor came back to life. I would never have found it without your help, thanks again.
Glad you found the problem and it's always a relief when it turns out to be an easy fix.
 

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