Upgrade the OEM lift pump

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.


Rember this...........you cant have any fun ifin yer scared.

Cheers, Kevin

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Last edited by Andy : 03-24-2007 at 02:52 PM.

[94Matt]

I would add, just to be on the safe side. It doesn't hurt to use the ecm plug to switch a relay with dedicated power going to the pump. This all but eliminates the possibility of low voltage hurting the pump.

That is how my Fass II wiring harness came, and I feel it's a good idea no matter where or what pump you're using.


Matt

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08 Dodge 2500 Q/C 4x4 long bed manual
07 Chevy 2500 crewcab, 4x4, D/A, long bed
93 Ford 250, 4x4, with 03 Cummins and manual

[Gary - K7GLD]

Originally Posted by 94Matt

I would add, just to be on the safe side. It doesn't hurt to use the ecm plug to switch a relay with dedicated power going to the pump. This all but eliminates the possibility of low voltage hurting the pump.

That is how my Fass II wiring harness came, and I feel it's a good idea no matter where or what pump you're using.


Matt

YUP - that;s what I do with my Carter 4600 pusher setup, has worked great for nearly 4 years and 40,000 miles so far...

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White '02 Quad cab, NV5600, GAUGES! Comp, Walbro, DTT SS intake, Rip's 4 in. exhaust, Don M's 1.6's, DSS, Frantz oil bypass & fuel filters, Amsoil air filter, MOBILE Ham Radio-IC-706, 600 watt amp, '88 Kit 24 ft. 5er, 418 HP/978 Tq., 24 ft KIT 5er.

[rweis]

Anyone else running a RASP?

Bob Weis

Originally Posted by rweis

Anyone else running a RASP?

Bob Weis

IMHO the RASP system or changing to a helix cam with fuel pump lobe/1st gen pump is the only systems out there that are better that the full phase fuel delivery I describe above..................remember my system still involves an electric pump and that is a downfall but it works for me

[94Matt]

Originally Posted by Whitmore

remember my system still involves an electric pump and that is a downfall

So does the rasp.

The rasp also leaks if you get the belt to tight. I like the idea, but as I always do, I think it's way overpriced for what it is.

__________________
08 Dodge 2500 Q/C 4x4 long bed manual
07 Chevy 2500 crewcab, 4x4, D/A, long bed
93 Ford 250, 4x4, with 03 Cummins and manual

The RASP is belt drive and goes with the RPM of the motor, this is a good thing, the only electric pump involved with the RASP is for priming a dry system (its the OEM l/p) it also is there for backup if you plumb it right

[94Matt]

The lp is used upon startup, and then shutoff via a pressure switch once the rasp gets going. In my opinion, that is more complication, and more things to potentially go wrong and leave you stranded someplace far from home, like Douglas.

__________________
08 Dodge 2500 Q/C 4x4 long bed manual
07 Chevy 2500 crewcab, 4x4, D/A, long bed
93 Ford 250, 4x4, with 03 Cummins and manual

OIC...........I didnt know it was used during startup ...........this is different, I guess it has to since the RASP cant pump fuel till the Cummins is running.

Thanks for the clarification Matt

[rweis]

Automatic backup not a good thing? Well, ok. Leave it off, but if the RASP quits for whatever reason you best switch off the engine within a few seconds.

Then you could crawl under the truck (generally dark and raining when this happens) and power up the lift pump on the frame rail. No problem.

OR you could connect it as an automatic backup and say "Opps, something happened to the RASP. I'll check it when I get home". (RASP belt is a cog belt, designed to be loose.)

Bob Weis

With all the lift pump activity going on I thought I would bring this back to the top as just another fueling option.

IMHO the 1psi of head pressure that is feeding the suction of my supply pump is key to the longivity of any fuel pump.

Like I said above no pump likes a vacumn

[Superduty]

Like I said above no pump likes a vacumn

That is a myth. It is false.

The only difference between a pump operating at 1 PSI of inlet pressure and 1 PSI of inlet vacuum is that the absolute pressure at the pump inlet is 15.7 PSIA versus 13.7 PSIA. It makes NO difference to the pump itself, provided the inlet pressures are sufficient to keep the pump full without cavitation. NONE. ZERO.

The only reason I comment on this is so that people understand the basics.

__________________
In Cummins we trust.

'99 Ford Superduty CC with 05 Cummins 325/600, BHAF, Donalson M090544 and ZF6 transmission. Tone ring mod.
Walbro 392 lift pump. 2 micron fuel filter on engine with filter lid pressure gauge.

I've been running a Walbro 392 since 2000. How long did your fuel pump last ?

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http://common-sense-diesel.blogspot.com/