Whit
Registered User
From 98.5 to 2002 the Cummins 5.9 has an OEM (original equipment manufacturer) lift pump #3990105 mounted on the drivers side of the block, The track record of the OEM pump on these models is poor.............very poor, I consider this OEM setup to be completly out of wack and often wonder what the heck Dodge/Cummins was thinking. The problem is that if the lift pump fails ..........not if but when is more like it, then the VP-44 injection pump will lose its cooling and lubricity that 70% of the lift pump duties are. A failed 150 dollor lift pump will most likely result in a code of PO181 Fuel injection pump failure at the cost of a bit over a grand if you do all the maintenance work. Thie Lift pump is expected to pull fuel from up to 10 feet away and also lift it about 20 " by my measurments, I can tell you that NO pump likes to operate at a vacuum and the end result will be death of the pump. I can also tell you that 27" of water column makes a pound so do the math here and you will understand what this pump is going thru and inturn understand why it doesnt seam to last long. Many have done their own R and D (research and development) to better the system, some have done OK but in the end the results arent much different. I have a fix of somewhat that worked for me for a few years that I am willing to share, this fix is not to spendy and the proven pressure results are much better then the OEM numbers, SO go to you local Cummins store and get an electrical pigtail for lift pump #3990105, for about 8 bucks, I am sure the Dodge dealer could get one but at a much higher price. Now this pigtail is about 4" long and plugs into the lift pump on one end ans the feed wire from the ECM on the other, OK now get some dirty close on cuz diesel stinks and you will get it on you before this is over, The Lift pump is located on the block, drivers side just under the fuel filter, Remove the fuel line banjo bolts (dont loose the gaskets)going into and out of the lift pump, there are 3 nuts on the bracket holding the lift pump on, use a 10mm wrench and take them off, also unplug the wireing, LEAVE THE BRACKET THERE, it has a gasket on the back side and if this bracket is removed you have an open crankcase. Now the original lift pump will need to be mounted on the frame rail back by the fuel tank so you have to fab up a bracket in an "L" shape so the pump can hang from the top of the L just like the old bracket, once the bracket is mounted and the pump is hanging you need to hook up the inlet and outlet fuel lines, This requires a bit of imagination but what I did was to get some metric hose barb fittings so one could simply cut the OEM fuel line and splice the barb fitting in there, Do the same for both inlet and outlet. Now the pigtail come to play, the new one you bought cut it in half, splice the pump end of the wiring in with long wires and make sure to use butt connectors and shrick tube to ge a good seal on the wireing, plug into the pump and run the wiring up to the original lift pump location where you will cut cut the wires to length and splice on the other end of the pigtail and plug it into its original wiring, NOW with this done the ECM will tell the pump to run just as it always did. The result will be now that you have better fuel psi and alot better WOT (wide open throttle) psi as well.
Phase 2 of this mod
Do same as above with the exception of ordering a fuel line kit consisting of all needed fuel line (Bigger too) and all needed fittings . This will also have a new pickup for inside the tank, a definate plus.
Phase 3 of this mod
Buy an inbed tank and plumb from it to the suction side of the lift pump................Whats that you say??? If there is fuel ABOVE the lift pump then the pump wont have to lift fuel anymore??? Thats right, rember 27" of water column makes a pound of pressure, yep thats right with a full tank of fuel in my bed tank I show a bit better that a pound of pressure with the pump OFF. Keep in mind that the fuel return line will now have to be relocated to flow into the inbed tank as well. Its also nice to have a level gauge in the cab so you can see what you got. Piece of cake.
Phase 4 of this mod
Now you have a totally worthless fuel tank under the truck thats not in use.........OH I have an Idea lets use it for storage and transfer the fuel as needed at a flip of the switch, cool idea and works so well.
Final phase of this mod
Use the OEM lift pump as a transfer pump from OEM tank to inbed tank and install a FASSII on the frame rail, The FASSII will recieve the OEM wiring from the ECM and the OEM lift pump will need new wiring and a switch in the cab.
Remember this...........you cant have any fun ifin yer scared.
Cheers, Kevin
Phase 2 of this mod
Do same as above with the exception of ordering a fuel line kit consisting of all needed fuel line (Bigger too) and all needed fittings . This will also have a new pickup for inside the tank, a definate plus.
Phase 3 of this mod
Buy an inbed tank and plumb from it to the suction side of the lift pump................Whats that you say??? If there is fuel ABOVE the lift pump then the pump wont have to lift fuel anymore??? Thats right, rember 27" of water column makes a pound of pressure, yep thats right with a full tank of fuel in my bed tank I show a bit better that a pound of pressure with the pump OFF. Keep in mind that the fuel return line will now have to be relocated to flow into the inbed tank as well. Its also nice to have a level gauge in the cab so you can see what you got. Piece of cake.
Phase 4 of this mod
Now you have a totally worthless fuel tank under the truck thats not in use.........OH I have an Idea lets use it for storage and transfer the fuel as needed at a flip of the switch, cool idea and works so well.
Final phase of this mod
Use the OEM lift pump as a transfer pump from OEM tank to inbed tank and install a FASSII on the frame rail, The FASSII will recieve the OEM wiring from the ECM and the OEM lift pump will need new wiring and a switch in the cab.
Remember this...........you cant have any fun ifin yer scared.
Cheers, Kevin
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