Auto Service Professional

OCT 2017

Magazine for the auto service professional

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Page 49 of 77

48 | ASP October 2017 Technical increased in steps by the transfer pump. e transfer pump is integral to the high pressure pump and is driven by the pump's main shaft. A portion of the fuel leaving the transfer pump flows to the lubrication valve which allows the fuel to lubricate the mechanical components of the high pressure pump. Fuel that is not used for pump lubrication is directed to the fuel volume control valve. is valve regulates how much fuel enters the inlet one-way check valve and the three main pump pistons. e three main pump pistons are actuated by the main shaft's offset journal. e shaft offset uses a free-spinning hub to make contact with the three main pump pistons. e pistons start their compression stroke when actuated by the offset journal and are returned to their rest position by spring pressure. Fuel is drawn into the main cylinder while the pistons return to rest position. e outlet check valve ball remains closed while fuel is drawn in by suction. Once the pistons start a compression stroke, the inlet one-way check valve closes using spring and fuel pressure and the outlet check valve opens due to the fuel pressure increase. After the high pressure fuel leaves the three main pump pistons, pressure is controlled by the fuel pressure control valve. A portion of the fuel leaves the pump and flows to the fuel cooler, with the rest of the fuel delivered to the high pressure fuel rails and injectors. High pressure pump problem e Ford Powerstroke 6.4L high pressure fuel pumps are problematic and more prone to damage if the fuel filter is not changed per Ford's maintenance schedule. A DTC P0088 (fuel rail/system pressure too high) indicates that the fuel pressure control valve in the pump is sticking. e pressure control valve cannot be repaired or replaced on its own, as it's integral to the pump assembly. e "killer code" P0088 requires a high pressure pump replacement. Depending on the source, replacement pumps run in the area of $1,000 to $1,600. Ford techs are seeing high pressure pump issues due to metal debris contamination. One likely cause is the failure to perform proper maintenance. e low pressure fuel pump/water separator/filter unit is mounted near the tank, on the frame. A water drain valve petcock is located on this unit, which allows draining water from the fuel. Ford recommends draining water every 30 days. However, due to the unit's location and the owners' negligence in not routinely opening this drain, water builds up in the fuel, contaminating and diluting lubrication for the high pressure pump. In the The high pressure fuel pump's front housing will be removed for inspection. Note the upper fuel feed and return threaded fittings at the top. Note the black secondary fuel filter housing at the engine's front left (at far right in this photo).

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