Copyright 2019 Discovery Owner's Association, Inc.

ISB Lift Pump Replacement

This is for those with early vintage Discovery's with the 5.9 Cummins ISB 24 valve engine.

I just completed installation on the lift pump on my 2000 vintage D. The pump is very easy to access from the bottom of the coach just below the upper fuel canister.

After much discussion, and studying the issues, I chose the Fass DDRP-02 model pump which I purchased new on Ebay from JD Auto and Truck in Westport Maine for $235.00 including shipping. It has a 4 year warranty.

I was warned to not use the Carter OEM pump because of the historic problems with this unit. Also since the VP44 injector pump depends on a good supply of fuel, and no less than 12 PSI of fuel pressure, it made the Fass system the choice. Fass has a very good reputation in the hotrod and power enhancement diesel market, and they have a very good technical support team that will discuss the issues, and advise on your particular problems or questions. Something lacking in today's mechanical world.

Prior to installation, I contacted Fass, and requested a pressure spring modification they will furnish. I got the spring by priority mail, and installed it prior to installing the pump on the coach. This spring will boost the output pressure of the pump by 3-5 psi. No charge for this spring. The pump is a direct replacement bolt on to the OEM bracket of the Cummins ISB 5.9 engine. It sits horizontally instead of vertical as the OEM Carter does. The line from the pump to the upper fuel filter is replaced with the banjo fittings furnished, and the special teflon 1/2 inch tubing.

The instructions are quite complete, but I discovered something that made the job much easier during my installation.

If you remove the upper fuel filter canister (remove the pump to filter banjo fittings as required) and the banjo bolt to the injector pump, unplug the water in fuel sensing wire, and the drain tube on the bottom. Two bolts removed from above removes the filter canister. When you do this, the 3 nuts holding the OEM pump are totally accessible from the top, and the new Fass pump much easier to install. I made a short stub bolt by cutting the head off a 5/16" bolt, threaded it into the Fass base, and allows you to align the other 2 holes to thread the supplied attachment bolts. Remove the stud, and install the 3rd retaining bolt.

I purchased a 30 psi fuel pressure gauge(Warner) from an Ebay vendor, and a 60 inch stainless 1/8th inch fuel hose and adapters from a local hot rod shop, so I could monitor the fuel pressure from the rear hatch of the engine compartment while hooking up. I also re-installed the idiot light to warn of low pressure which is visible from the pilots chair in the coach. This fuel monitoring system is installed on the banjo between the upper fuel canister, and the VP 44 injector pump to monitor the filters and pump function. A 1/8th inch Brass Tee and short nipple was necessary for this hookup, available at NAPA auto parts.

I now have a pump that supplies 18 psi to my VP44 injector, and 75 gpm which will guarantee the VP44 will have adequate fuel flow and pressure. The pressure holds steady at WOT.

The job would have been much easier with 2 guys, but I completed the job in 2 short days, and a lot of stiff joints after the fact. This was a very greasy job. Total cost of the job was less than $300.00

Prior to the installation, I checked the fuel pressure on the original installed Carter pump and it was 7psi. I know this was a high reading because my idiot light was blinking at 5.5psi. Had I not changed the pump, I would have possibly been installing a new VP44 injector pump at lots of bucks. Low pressure and low fuel supply is a killer of the VP44.

Submitted by - Gary Bogart


The DISCOVERY OWNERS ASSOCIATION, INC, was formed to promote the sharing of information and the camaraderie of fellow Discovery motorhome owners. Membership in the club is limited to owners of Fleetwood Discovery motorhomes.


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