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Regarding the VP-44 injector pump and its use in RV's. I understand that much of this information is beyond many on the Forum, but it should provide a coach owner a good source of questions. I hope that if the reader needs some clarification, they will ask questions and hopefully get some good feedback; enabling them to ask informed questions at service centers and Cummings customer service engineering help line. This injector pump was used from January of 1998 to 2002, NOTE ! Some of the 2003 year coach's where built on 2002 chassis and a smaller version was used on Diesel power cars and boats in the same time frame. I have tried to combine information from a number of sights to fill in the gaps. This is a lengthy article, if one reads all the information. It is information meant to help owners ask the right questions. Also included pictures of connectors and adapters one might need to complete a good upgrade to improve performance and reliability. Some information from Cummings, Dodge truck owner sights and sights that have collected a considerable amount of road test data while monitoring fuel lift pump pressure information and what a flow rate pressure valve on the VP-44 fuel return output line that can cause them to fail. I also added some personal thoughts highlighted in red where I piggybacked to the original authors information. I tried to clarify the differences regarding the engine applications and where some of the big bugaboo's are. There Is A lift pump Pressure sweet point one should try to reach and use. Fuel System - General Information from Cummins Link- http://dodgeram.org/tech/dsl/ISB/Vp44.htm The VP44 is an electronic fuel injection pump manufactured by Bosch®, that can vary fueling and injection timing based on input from the electronic control module (ECM). This pump has its own electronic control unit, the fuel pump control module (FPCM), which contains fueling, timing, and diagnostic data. The fuel pump control module (FPCM) communicates with the engine controller (ECM) to obtain information on desired fueling and timing. The fuel pump control module (FPCM) responds to the ECM's commands by consulting the fueling data and timing in its memory and actuating the fueling and timing solenoids. A fuel temperature sensor is located inside the VP44 pump to compensate for changes in the temperature of the fuel. The pump also contains a speed sensor (IAT) that gives the fuel pump control module (FPCM) data on the position and speed of the pump shaft. A reference pulse that marks top dead center (TDC) of cylinder No. 1 is sent from the ECM once every pump revolution. By comparing this reference pulse from the ECM to the position signal from the speed sensor (IAT), the fuel pump control module (FPCM) can reference the pump's position in relation to the engine's position. This allows the fuel pump control module (FPCM) to adjust the pump timing to compensate for minor position differences between the fuel pump shaft and the engine camshaft. If the difference between the pump position and engine position becomes too great, then a fault will be logged in the fuel pump control module (FPCM). In addition to the engine position reference pulse, the fuel pump control module (FPCM) also receives timing and fueling commands from the ECM. The fuel pump control module (FPCM) controls the timing and fueling through two solenoids located in the pump. The timing solenoid controls the position of a cam ring inside the pump by varying internal transfer pump pressure. The cam ring has evenly spaced lobes around its inner diameter. The pumping plungers ride on rollers that rotate inside this cam ring. The rollers follow the inner diameter of the cam ring and push the pumping plungers inward whenever a cam lobe is encountered, thus building injection pressure. By rotating the cam ring with the timing solenoid, the fuel pump control module (FPCM) is able to advance and retard the injection timing by making the rollers contact the cam lobes either earlier or later. The second solenoid in the pump is used to meter fuel to the injectors. The solenoid opens the fuel metering valve to allow fuel from the supply pump to flow into the pumping chamber. Once the pumping chamber is charged with fuel, the solenoid valve closes. This traps the fuel in the chamber and allows injection pressure to build. The fuel is routed to the correct injector by the pump distributor. The distribution port on the distributor aligns with one of the six outlet ports to distribute fuel to a given injector. Once the desired amount of fuel has been injected, the solenoid valve opens, causing the pressure in the pumping chamber to bleed down, which ends injection. The cycle then begins again for the next cylinder. The fuel injection pump (VP44) is an electronic rotary distributor pump. The pump performs four basic functions: Producing the high fuel pressure required for injection Metering the exact amount of fuel for each injection cycle Distributing the high-pressure, metered fuel to each cylinder at the precise time Varying the timing relative to engine speed. A cam ring with three plungers, a rotor, and an electronically controlled fueling solenoid valve is used to develop and distribute the high pressure required for injection. A worn or damaged internal transfer pump, plunger, or fueling valve can affect the pressure and the amount of fuel injected, thus reducing the power from the engine. Generally, if the fuel-injection pump is injecting fuel from one outlet, it will deliver from all outlets. VP44 Timing Principles Timing in the VP44 is controlled by an internal timing piston coupled to a cam ring inside the pump. The timing piston is moved by fuel pressure. The amount of fuel pressure in the timing piston assembly housing is controlled by an internal transfer pump and a pulsating timing solenoid valve. As the pump speed increases, the fuel pressure to the timing piston assembly also increases. Based on the inputs from the fuel pump control module (FPCM), the timing solenoid valve pulses to vary the pressure to move the timing piston, which results in the cam ring moving to the desired position to achieve the commanded timing. The more pressure created by the internal transfer pump and timing solenoid valve, the more the timing will advance; therefore, timing range capability is increased at higher rpms. The ISB engine is equipped with an electric-powered lift pump. Fuel flow begins as the fuel lift pump pulls fuel from the supply tank. This electric lift pump supplies low-pressure fuel (10 to 12 psi) to the filter head, through the filter, and then to the electronic distributor injection pump. The electronic distributor pump builds the high injection pressures required for combustion and routes the fuel through individual high-pressure fuel lines to each injector. When the high-pressure fuel reaches the injector, the pressure lifts the needle valve against the spring tension to let the fuel enter the combustion chamber. Any leakage past the needle valve enters the fuel drain manifold in the cylinder head. The fuel in the manifold exits at the rear of the cylinder head and is routed to the fuel tank. The fuel that is returned from the fuel injection pump is also routed back to the fuel tank. ONE critical point to understand in the paragraph regarding the ISB OEM lift pump pressure that is listed as 10 to 12 psi. Please remember this as you continue to read the fallowing attached information. I will try to answer your questions and if by chance I'm on the road an not on line, there are some real good members on the forum that can a good job and some are better then me and spent more time working on Diesels for sure. Rich. Fuel Pressure Specification For Bosch _VP-44.pdf