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Bleeding a Lucas Injector pump on Ford 755

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Bob

07-09-2001 22:34:38




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We just replaced the fuel filter and had the injectors rebuilt on our backhoe, and have gone by the book to bleed the system. First the fuel filter, then injector pump, then the injector lines at the injectors. Bleeding the filter and the injector pump worked great, but we can't get any fuel out of the injector lines (the high pressure side of the pump). We've verified that we get good fuel flow to the pump. The fuel shutoff appears to be in the correct position (based on how it has always worked).

Any ideas, short of having a tech. look at the injector pump? It seems like it should be pretty simple, so I keep thinking I'm missing something.

By the way, everything worked fine a couple of weeks ago, when we noticed it was loosing power under load, so we found one of the injectors was weeping. We had them all rebuild.

Thanks

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texadian

07-10-2001 09:59:34




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 Re: Bleeding a Lucas Injector pump on Ford 755 in reply to Bob, 07-09-2001 22:34:38  
Sounds like the rack may be stuck in the shut off position. Move the throttle to maximum speed, push the excess fuel button in the pivot shaft for the fuel shut off lever, you should hear a click as the rack springs back past its normal max fuel delivery position. Sometimes you can free the rack by removing the injection pump side cover and push the rack rearwards with your fingers. Rearwards is more fuel; forward is fuel shut off. If this works, use some diesel fuel coditioner to clean up the system.

If the rack is in full or excess fuel delivery position, the pump and filters are bled and still won't pump fuel up to the nozzles, there's something more seriously wrong with the pump.

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Bob

07-10-2001 21:57:59




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 Re: Re: Bleeding a Lucas Injector pump on Ford 755 in reply to texadian, 07-10-2001 09:59:34  
Thanks for the suggestion. The rack was stuck in the closed position. After working it a few times we were able to fire up the engine and bleed each of the high pressure lines.

Now we have another issue with the number 4 injector. When the system is at about half throttle and above and we loosen the fitting to bleed the line we get pressurized fuel coming out. However, at idle and low throttle there is nothing coming out. It appears that the mechanism that pressurizes the number 4 line is not working correctly.

Any ideas on this issue? Could diesel conditioner possibly clear this up?

Thanks again for your earlier suggestion.

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texadian

07-12-2001 14:48:52




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 Re: Re: Re: Bleeding a Lucas Injector pump on Ford 755 in reply to Bob, 07-10-2001 21:57:59  
Possibilities:
1. The fuel delivery valve, a one-way check valve on top the injection pump, for No. 4 nozzle might be leaking back; it's supposed to hold a few hundred psi of residual fuel pressure in the high pressure line between the pump and the nozzle between successive plunger strokes. You need a special 36 point (serrated) socket to remove and reinstall the delivery valve (45 Lbs-ft.torque). 2. The pump plunger and its barrel are worn. 3. Someone's moved with the fork that rotates no. four injection pump plunger (and varies the fuel delivery). I strongly recommend that you do not try to reset this on the tractor. If a new delivery valve doesn't help, get the pump to a good diesel pump shop for recalibration.

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Daryl

07-10-2001 13:10:34




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 Re: Re: Bleeding a Lucas Injector pump on Ford 755 in reply to texadian, 07-10-2001 09:59:34  
Thanks Texadian, Bob and I are working on the same 755 and we're going to take your advice. Is it significant that when we push the excess fuel button in that it does not "click" or stay in or anything? I'm thinking that this is a good indication that the rack is stuck in the "off" position.



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