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John Deere Tractors Discussion Forum

720 d fuel pressure

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06-28-2020 14:36:27

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I just had my engine apart on my 720 diesel. I'm having a time getting the fuel system bled. It seems to be running on 2 cylinders now but im showing 0 fuel pressure at the filters. The transfer pump and return fitting were recently rebuilt.

Think I just need to bleed it more?

Is it possible maybe the return fitting has dirt in it, holding it open at that might not be letting it build pressure? Or is that not how it works?

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wore out

06-28-2020 15:27:06

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 Re: 720 d fuel pressure in reply to JL2510, 06-28-2020 14:36:27  
Is it returning a significant amount of fuel? If returning fuel it is getting through adapter or relief valve without building pressure, if little or no return, the transfer pump may be weak.

I can't remember the exact details, but there was an "upgrade" kit available to a different pressure relief valve, raised fuel rail pressure, IIRC?

You mention having the transfer pump "rebuilt", what was done, new gear/shaft to seal it up? Really nothing else that could be done if the housing is worn?

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06-28-2020 16:13:11

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 Re: 720 d fuel pressure in reply to wore out, 06-28-2020 15:27:06  
The early 720s had lower fuel pressure and no return line to the tank. The later ones and the 730s had higher pressure and a return line. Mine is an early 720 but I upgraded everything to the new style, high pressure set up and sent my transfer pump to Renaissance Tractor for rebuilding. I forget now what he did but he said he was getting 45psi out of it. I'm showing nothing now though.

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wore out

06-29-2020 08:05:31

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 Re: 720 d fuel pressure in reply to JL2510, 06-28-2020 16:13:11  
So, have you checked, is there a significant return flow coming out of the valve?

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