losing prime

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Jul 21, 2011 | 08:48 PM

Jayme Duty

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losing prime

The truck is a 94 cc f-350 7.3DI has 288,000miles and if it sits for about 4-5days or longer it will lose its prime and I have to crank and crank to get fuel back to the injectors, What is the main cause of this

Jul 21, 2011 | 08:54 PM

F350-6

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From: Texas

Are you sure it's fuel and not an oil issue? Next time it sits for a few days, check the oil level in the HPOP reservoir to see if that's what is draining down before you try to start it.

Jul 21, 2011 | 08:57 PM

Action4478

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Most likely the HPOP res is draining down .. It can happen for quite a few reasons ..Bad Injector O rings is one of them ...

Next time it sits for a few days , look in the res before starting it . the oil needs to be 1/2 inch or so from the top of the res..

Jul 21, 2011 | 09:43 PM

Jayme Duty

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Thanks for the replies, I am completely new to the DI motor, i have always had IDI's. I have no idea what the HPOP reservoir is or where it is located. I am also confused why the oil would keep it from starting. if anybody has pics that would be great

Jul 21, 2011 | 09:57 PM

Action4478

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The res is rectangular on the front of the motor . the oil pressure srensor & a hex screw is where you check the oil ..

Jul 22, 2011 | 06:15 AM

427 fordman

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From: Plankinton, SD

The res is in the bottom of the picture. Not a great pic but its there. Rectangular like Rick said. The high pressure oil is used to fire the injectors.

Jul 22, 2011 | 06:45 AM

DIYMechanic

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From: Orrville, Ohio

HERE Is some light reading if you want to better understand the design and function of the PSD DI fuel system. Basically the injectors are driven by a High Pressure Oil Pump (HPOP) that uses high pressure oil to provide the pressure to drive the fuel injectors. The reservoir you are checking is the reservoir that holds the oil for the HPOP. The low pressure oil pump (in the oil pan) fills the reservoir, but if the level leaks down while the truck is sitting, then you have to crank the engine until the reservoir is full enough to provide oil to the HPOP and fire the injectors. The design of this system is why it is very important to our engines that you have clean, diesel rated oil.

Welcome to the PSD. We are all here to learn something.