Ultimate Diesel Builder's Guide - - Contents - Text/pho­tog­ra­phy: Chris Tobin

Up­grad­ing the fuel sys­tem on a Cum­mins-pow­ered work truck

Proper oper­a­tion of the fuel sys­tem in any diesel en­gine is of vi­tal im­por­tance, es­pe­cially with mod­ern, high-pres­sure com­mon rail en­gines. Get­ting the fuel from the tank to a Cum­mins com­mon rail en­gine ef­fi­ciently in­volves uti­liz­ing a low-pres­sure lift pump in or near the tank feed­ing an en­gine-driven, high-pres­sure CP3 pump to pres­sur­ize the fuel rail and feed the in­jec­tors.

Roy Dorn’s 2006 Dodge 3500 work truck has more than 207,000 miles on the odome­ter and seemed to have a hard time keep­ing up with the de­sired rail pres­sure in the hot­ter tunes that the crew at Beans Diesel Per­for­mance in­stalled in the truck. When the truck was strapped to the dyno and run­ning through the new EFILIVE tunes, it made much more power than stock in all five of the tune po­si­tions, but strug­gled to main­tain de­manded rail pres­sure es­pe­cially at higher rpm.

Af­ter driv­ing the truck for a few thou­sand miles, Dorn no­ticed it started to feel as though it was los­ing power in tune 3 and some­times in tune 2. He took it to Beans Diesel Per­for­mance where the team, know­ing that the orig­i­nal fac­tory fuel sys­tem had more than 200,000 miles on it, de­cided it was a good time to up­grade both the lift pump and high-pres­sure CP3. They also rec­om­mended that the new Air­dog II-4G fuel pump and fil­ter sys­tem be in­stalled with one of their own BDP fuel tank sumps and a Fleece Per­for­mance Engi­neer­ing Pow­er­flo 750 CP3.


In­stalling the Air­dog II-4G not only by­passes the fail­ure-prone and typ­i­cally weak in-tank fac­tory lift pump on this model Ram with a stronger pump, it also re­moves en­trained air from the fuel, fil­ters the fuel and re­moves wa­ter. The fourth gen­er­a­tion (4G) de­sign uses a self-align­ing, low am­per­age mo­tor that is more ef­fi­cient and lasts longer than pre­vi­ous de­signs. It also fea­tures an in­ter­me­di­ate pump shaft that sep­a­rates the pump mo­tor from the fuel in the dual-feed gero­tor pump. Rather than suck­ing fuel from the tank us­ing a draw straw or us­ing the in­ter­nal pick-up, the team at Beans sug­gests us­ing their fuel tank sump in­stalled in the bot­tom of the tank to grav­ity feed the Air­dog pump. Since the Air­dog uses

an easy-to-ac­cess fuel fil­ter and wa­ter sep­a­ra­tor, we also opted to use a Fleece Per­for­mance Cum­mins fuel fil­ter delete block to elim­i­nate the fac­tory fil­ter, which is hard to reach for ser­vice and no longer nec­es­sary.


The Fleece Per­for­mance Engi­neer­ing Pow­er­Flo 750 CP3 is a new Bosch CP3 that the team at Fleece mod­i­fies with a 10mm stroke cam (up from 8.5mm stroke in a stock CP3) to en­hance flow ca­pa­bil­ity. The Pow­er­flo 750 also elim­i­nates the 3,000 rpm fuel flow re­stric­tion that is in­her­ent in the fac­tory CP3 de­sign, al­low­ing it to de­liver more fuel at higher rpm where you need it most.

As the name im­plies, it is ca­pa­ble of keep­ing up with the fuel de­mands of a 750 rear-wheel-horse­power en­gine with the proper com­ple­ment­ing up­grades (they have mea­sured as much as 822 hp to the wheels in a sin­gle Pow­er­flo 750 in­stal­la­tion). They are each in­di­vid­u­ally tested in-house to make sure they are ready to de­liver right out of the box. Since the Pow­er­flo 750 is a com­pletely new unit, there is no need for a core charge, al­low­ing own­ers to sell their old CP3 to help off­set the cost of the new unit.


Af­ter we brought the truck and our shiny new parts up to the Beans Diesel Per­for­mance shop in Wood­bury Tenn., Jack Grubb went to work on the big truck. To di­ag­nose the poor run­ning Dorn had been ex­pe­ri­enc­ing over the past few days, Grubb con­nected a shop lap­top and flashed the tun­ing back to stock and the truck was still feel­ing slug­gish on the top end of the tach.

Since the trou­ble stayed with the truck af­ter the EFILIVE tun­ing was re­verted to stock, he knew the prob­lem was with the truck and sus­pected the fuel sys­tem. Some data log­ging re­vealed that it was now hav­ing trou­ble main­tain­ing rail pres­sure even with stock tun­ing show­ing that the truck re­ally needed a fuel sys­tem up­grade.

Grubb com­pleted the fuel sys­tem up­grade in about five and a half hours, in­clud­ing the typ­i­cal slow­downs re­lated to our pho­tog­ra­phy. Ex­pe­ri­enced Diy­ers should be able to com­plete the in­stal­la­tion in about a day with­out too much dif­fi­culty. Al­ways be sure to prac­tice safe shop tech­niques, es­pe­cially when rout­ing hoses and wire har­nesses near hot or mov­ing items in the en­gine bay or un­der­neath the truck. Fol­low along over the next few pages for an over­view of the in­stal­la­tion process.

6 Be­fore BDP diesel tech­ni­cian Jack Grubb gets starts re­mov­ing the old CP3, he sprays off the area sur­round­ing the fuel lines with brake cleaner to pre­vent de­bris from en­ter­ing the fuel sys­tem. No­tice that the fac­tory fuel fil­ter (see ar­row) is...

1 The AEM in­take is the main thing you see when you open the hood; in this ar­ti­cle, we’ll be ad­dress­ing is­sues that aren’t as easy to see while we up­grade the fuel sys­tem.

2 A new Fleece Per­for­mance Engi­neer­ing Pow­er­flo 750 CP3 high-pres­sure fuel pump is the heart of our fuel sys­tem up­grade. The 10mm stro­ker pump will have no prob­lems keep­ing up with the fuel de­mands in Dorn’s truck, even if he up­grades to larger...

3 To get the fuel from the tank to the CP3, Dorn opted to go with the new Air­dog II-4G fuel pump and fil­ter sys­tem, which will be re­plac­ing the weak fac­tory in-tank lift pump.

5 Rather than suck­ing fuel out of the top of the tank, we in­stalled a Beans Diesel Per­for­mance fuel sump to let grav­ity help us get the fuel from the bot­tom of the tank. The kit even in­cludes the prop­erly sized hole saw to cut the hole in the bot­tom...

4 Since the Air­dog’s fil­ter and wa­ter sep­a­ra­tor are eas­ier to get to than the fac­tory fuel fil­ter, we chose to in­stall a Fleece fil­ter delete that even comes with a cool koozie to keep your fa­vorite adult bev­er­age cold un­til af­ter you fin­ish the...

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