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Cummins Lift Pump 101, 201, Graduate Course
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<blockquote data-quote="DiamondSCattleCo" data-source="post: 406352" data-attributes="member: 2862"><p>I wrote this up for another list, but thought some may find some use for it here:</p><p></p><p>It seems like this topic comes up once in awhile on here, so I'll rattle</p><p>this off to clear up misconceptions and hopefully prevent guys from spending</p><p>big dollars on what amounts to a bunch of un-needed junk.</p><p></p><p>First, to clear up a fallacy I see repeated over and over again:</p><p></p><p>Dodge lift pumps, in their stock location do NOT suck fuel. Or at least,</p><p>not enough to remotely hurt an electric pump. If you don't believe me, fill</p><p>up your fuel tank and pull the inlet line off your lift pump. Leave it in</p><p>the air at about the level of the lift pump inlet and let the fuel run out</p><p>of the tank. You'll drain the 30 gal tank in about 15 minutes. Thats 120</p><p>GPH flow. The stock lift pump is only a 90 GPH pump. You do the math.</p><p></p><p>1998 - 2002 VP44 equipped trucks.</p><p></p><p>As has been mentioned, these trucks are prone to lift pump failure, even at</p><p>stock power. These pumps are a pretty basic design pump. About the only</p><p>thing fancy on them is an internal bypass valve (check ball) to prevent over</p><p>pressure.</p><p></p><p>I sat down with my local Dodge tech and pulled down a whack of lift pumps.</p><p>Well, a dozen. But it felt like a whack. On 10 of these pumps, the check</p><p>ball bypass valve was not functioning. One even had the checkball driven</p><p>through its spring and was on the wrong side of the spring. Of the other 2</p><p>failures, we had 1 failed electric motor and 1 broken teflon bushing that</p><p>holds the pump vein to the motor. In other words, only 1 failure in 12 that</p><p>could remotely be blamed on long fuel draws (the burnt motor). Since that</p><p>little episode, I've pulled down a few more pumps and seen bypass valve</p><p>failures in EVERY single one of them.</p><p></p><p>In other words, these guys yapping about the lift pump failures being due to</p><p>the long _pull_ from the fuel tank are full of crap. And that includes</p><p>Dodge with their goofball in-tank solution.</p><p></p><p>So why the checkball failures? As the VP44 is using fuel, the line pressure</p><p>between the lift pump and the VP44 drops. The VP44 and subsequent injection</p><p>system has a max flow rate of around 75 GPH in stock trim. So that means</p><p>that the lift pump is able to pump more fuel than the VP44 can consume, even</p><p>at WOT. The design of the VP44 compounds the issue, in that it doesn't just</p><p>smoothly flow fuel but rather takes little gulps of fuel at a time via its</p><p>own little sliding vein pump. Which means that the lift pump check valve is</p><p>continuously working.</p><p></p><p>However, this wouldn't normally be a problem, except for one thing: At each</p><p>joint in the fuel system (2 at the lift, 2 at the fuel filter, 1 on the VP44</p><p>pump inlet) there are banjo bolts with crossdrilled holes. These banjo</p><p>bolts, with their small holes, are not even remotely capable of flowing 90</p><p>GPH. So this means that the lift pump is trying to pound 90 GPH against a</p><p>fitting only capable of flowing _maybe_ 65 GPH. In other words, the flow of</p><p>fuel through the system is disjointed and erratic as it passes through each</p><p>joint. Which means that the pump bypass valve is flicking on and off like</p><p>mad, well past the design limits of the checkball/spring combination causing</p><p>early failure.</p><p></p><p>So how do you fix it? At stock and near stock horsepower levels, its easy.</p><p>Make the banjo bolts flow more by opening up the cross drilled holes from</p><p>the stock size of .135" to .187". I found this was plenty large enough to</p><p>allow fuel to flow smoothly in the system and reduce the stress on the lift</p><p>pump. The larger banjo bolts would reliably support 300 to 320 HP. The</p><p>only proof I can give you is that trucks putting the banjos on went from</p><p>failures every 30,000K to still running strong at 100K or more.</p><p></p><p>Past the 300 HP level or for guys who spent alot of time at WOT, we found</p><p>the banjos still didn't quite flow enough. The answer was to replace the</p><p>banjo fittings all together with custom built -8AN fittings and -8 hose. I</p><p>did this between the lift pump and fuel filter housing, and between the fuel</p><p>filter housing and injector pump. This worked very well up to around 375HP.</p><p></p><p>Past that point however, I found the stocker lift pump couldn't handle the</p><p>bursts of fuel required at WOT and eventually the internal bypasses would</p><p>fail again. The answer was simple. Find a higher flow pump, around 150</p><p>GPH. We didn't need the additional fuel flow, but these higher flowing</p><p>pumps had heavier built check valves that could handle the abuse that the</p><p>VP44 exacted on them. I preferred the Holley series and the Product</p><p>Engineering pumps, however others had great luck with Carters too. There</p><p>were alot of issues with Holley pump quality for awhile, however we found it</p><p>was simply a matter of pulling them apart and cleaning up some of the</p><p>castings.</p><p></p><p>I looked at mounting the pumps back by the fuel tank, but realized that in</p><p>the snowbelt those pumps were fully exposed to the elements, and we knew</p><p>from competitor experience and the RV market that pusher pumps often rot</p><p>away back there. Not to mention that pushing that distance was asking alot</p><p>from a small pump, and often times the teflon bushings that mate the veins</p><p>to the electric motor would disintegrate back there. It is pure fallacy</p><p>that small electric pumps can push diesel fuel long distances without</p><p>wearing on the pump drive components, but rather the pump has to be</p><p>specifically designed to do that. None of the cheap $100 pumps are designed</p><p>for this style of application. As a final killer to the idea of mounting</p><p>pumps back on the frame rail, I noticed that many pumps sat level with the</p><p>bottom of the frame, or even slightly below. For anyone driving in deeper</p><p>snow, mud, or off-roading, that pump was just ASKING to get torn off and</p><p>leave them stranded.</p><p></p><p>So I chose to mount under the hood area, up on the frame rail where it</p><p>starts to curve upwards for the front suspension. I noticed this area was</p><p>well protected from salt and water spray by the front axle, and was high</p><p>enough up that it couldn't be tore off when off-road. Also remembering how</p><p>much fuel transfer there was from the tank, and I thought I'd found the</p><p>perfect mounting spot. I called both Holley and PE, spoke to the actual</p><p>engineers in charge of designing the pumps, and verified that a distance</p><p>draw wouldn't hurt either of these pumps. Indeed, I got the same response</p><p>from both companies: Horizontal distance draws do not hurt their pumps, but</p><p>rather its the vertical draw you need to worry about. Both companies</p><p>recommended that I not draw more than 2 feet in the vertical (distance from</p><p>bottom of pickup tube to pump inlet), and I was well within that tolerance.</p><p></p><p>I built a custom bracket that used existing holes in the frame to mount the</p><p>pump, but there was no issue with drilling for a different bracket either.</p><p></p><p>Mounted in this location, I found that there was ZERO pull down on fuel</p><p>pressure, no matter what pump I used, no matter what horsepower level I was</p><p>at. I've got customers sitting at 600 - 650 HP on straight diesel, and have</p><p>been running strong for three or four years with the SAME pump in place.</p><p></p><p>As a side note, this lift pump failure syndrome is not limited to ISB</p><p>Dodges, but rather all VP44 ISB equipment. And the one thing they all have</p><p>in common are those small banjo bolts. Lift pump location varies, and they</p><p>all experience pre-mature failure.</p><p></p><p>2003 and up CP3 equipped trucks.</p><p></p><p>The little pump that comes stock with CP3 equipped trucks is a pretty weak</p><p>kneed little critter, but it is well suited to stock horsepower levels with</p><p>only a little draw down on pressure at WOT throttle loads. I never did much</p><p>experimentation at stock power levels, however I did install higher flow</p><p>banjo bolts. As I expected, they didn't do much to affect flow, as the CP3</p><p>equipped trucks are already sitting at what I considered the upper limits</p><p>powerwise for high flow banjos. I do however believe that the higher</p><p>flowing banjo would help with early failures on stock powered pickup trucks.</p><p></p><p>As soon as I started modifying the truck, I immediately replaced the lines</p><p>with -8AN lines, but left the stock lift pump in place. I found that any</p><p>kind of power increase over stock would immediately show a pressure</p><p>decrease, even with the large lines installed. So I built an adapter, and</p><p>stuffed a 14PSI 140 GPH Carter pump in the same location as we did with the</p><p>VP44 equipped trucks. End result was ZERO draw down on pressure, even at</p><p>the 500 HP level. I ran like this for a couple years, and never once had a</p><p>burp out of the cheap Carter lift.</p><p></p><p>So what can you do to your truck?</p><p></p><p>If you plan on buying an aftermarket fuel system for your truck, skip by ALL</p><p>the goofy pusher pumps. Complete waste of money, and you ruin the utility</p><p>of your truck. The FASS system and AirDog mount back on the frame rail by</p><p>the tank, and their additional filters hang BELOW the frame rails. To my</p><p>way of thinking, this is extremely bad design.</p><p></p><p>If you plan on modifying your truck past 300 HP, find yourself a system that</p><p>replaces all the lines and banjos forward of the lift pump. If these lines</p><p>are not replaced, you're wasting your money on everything else. Depending</p><p>on your horsepower level, you may or may not have to replace the pump. If</p><p>you want to build your own system (the cheapest route), contact Earls and</p><p>get a set of their aluminum -6 adapters. They're available off the shelf.</p><p>Then go to NAPA and buy some pushlock fittings and -6 diesel safe pushlock</p><p>hose. Then buy a 140+ GPH pump from favorite manufacturer and mount it</p><p>under the hood where its protected. I know I used -8 lines, but -6 would be</p><p>lots right up to 500 HP.</p><p></p><p>I hope this helps, and I hope that it saves some of you some money.</p><p></p><p>Rod</p></blockquote><p></p>
[QUOTE="DiamondSCattleCo, post: 406352, member: 2862"] I wrote this up for another list, but thought some may find some use for it here: It seems like this topic comes up once in awhile on here, so I'll rattle this off to clear up misconceptions and hopefully prevent guys from spending big dollars on what amounts to a bunch of un-needed junk. First, to clear up a fallacy I see repeated over and over again: Dodge lift pumps, in their stock location do NOT suck fuel. Or at least, not enough to remotely hurt an electric pump. If you don't believe me, fill up your fuel tank and pull the inlet line off your lift pump. Leave it in the air at about the level of the lift pump inlet and let the fuel run out of the tank. You'll drain the 30 gal tank in about 15 minutes. Thats 120 GPH flow. The stock lift pump is only a 90 GPH pump. You do the math. 1998 - 2002 VP44 equipped trucks. As has been mentioned, these trucks are prone to lift pump failure, even at stock power. These pumps are a pretty basic design pump. About the only thing fancy on them is an internal bypass valve (check ball) to prevent over pressure. I sat down with my local Dodge tech and pulled down a whack of lift pumps. Well, a dozen. But it felt like a whack. On 10 of these pumps, the check ball bypass valve was not functioning. One even had the checkball driven through its spring and was on the wrong side of the spring. Of the other 2 failures, we had 1 failed electric motor and 1 broken teflon bushing that holds the pump vein to the motor. In other words, only 1 failure in 12 that could remotely be blamed on long fuel draws (the burnt motor). Since that little episode, I've pulled down a few more pumps and seen bypass valve failures in EVERY single one of them. In other words, these guys yapping about the lift pump failures being due to the long _pull_ from the fuel tank are full of crap. And that includes Dodge with their goofball in-tank solution. So why the checkball failures? As the VP44 is using fuel, the line pressure between the lift pump and the VP44 drops. The VP44 and subsequent injection system has a max flow rate of around 75 GPH in stock trim. So that means that the lift pump is able to pump more fuel than the VP44 can consume, even at WOT. The design of the VP44 compounds the issue, in that it doesn't just smoothly flow fuel but rather takes little gulps of fuel at a time via its own little sliding vein pump. Which means that the lift pump check valve is continuously working. However, this wouldn't normally be a problem, except for one thing: At each joint in the fuel system (2 at the lift, 2 at the fuel filter, 1 on the VP44 pump inlet) there are banjo bolts with crossdrilled holes. These banjo bolts, with their small holes, are not even remotely capable of flowing 90 GPH. So this means that the lift pump is trying to pound 90 GPH against a fitting only capable of flowing _maybe_ 65 GPH. In other words, the flow of fuel through the system is disjointed and erratic as it passes through each joint. Which means that the pump bypass valve is flicking on and off like mad, well past the design limits of the checkball/spring combination causing early failure. So how do you fix it? At stock and near stock horsepower levels, its easy. Make the banjo bolts flow more by opening up the cross drilled holes from the stock size of .135" to .187". I found this was plenty large enough to allow fuel to flow smoothly in the system and reduce the stress on the lift pump. The larger banjo bolts would reliably support 300 to 320 HP. The only proof I can give you is that trucks putting the banjos on went from failures every 30,000K to still running strong at 100K or more. Past the 300 HP level or for guys who spent alot of time at WOT, we found the banjos still didn't quite flow enough. The answer was to replace the banjo fittings all together with custom built -8AN fittings and -8 hose. I did this between the lift pump and fuel filter housing, and between the fuel filter housing and injector pump. This worked very well up to around 375HP. Past that point however, I found the stocker lift pump couldn't handle the bursts of fuel required at WOT and eventually the internal bypasses would fail again. The answer was simple. Find a higher flow pump, around 150 GPH. We didn't need the additional fuel flow, but these higher flowing pumps had heavier built check valves that could handle the abuse that the VP44 exacted on them. I preferred the Holley series and the Product Engineering pumps, however others had great luck with Carters too. There were alot of issues with Holley pump quality for awhile, however we found it was simply a matter of pulling them apart and cleaning up some of the castings. I looked at mounting the pumps back by the fuel tank, but realized that in the snowbelt those pumps were fully exposed to the elements, and we knew from competitor experience and the RV market that pusher pumps often rot away back there. Not to mention that pushing that distance was asking alot from a small pump, and often times the teflon bushings that mate the veins to the electric motor would disintegrate back there. It is pure fallacy that small electric pumps can push diesel fuel long distances without wearing on the pump drive components, but rather the pump has to be specifically designed to do that. None of the cheap $100 pumps are designed for this style of application. As a final killer to the idea of mounting pumps back on the frame rail, I noticed that many pumps sat level with the bottom of the frame, or even slightly below. For anyone driving in deeper snow, mud, or off-roading, that pump was just ASKING to get torn off and leave them stranded. So I chose to mount under the hood area, up on the frame rail where it starts to curve upwards for the front suspension. I noticed this area was well protected from salt and water spray by the front axle, and was high enough up that it couldn't be tore off when off-road. Also remembering how much fuel transfer there was from the tank, and I thought I'd found the perfect mounting spot. I called both Holley and PE, spoke to the actual engineers in charge of designing the pumps, and verified that a distance draw wouldn't hurt either of these pumps. Indeed, I got the same response from both companies: Horizontal distance draws do not hurt their pumps, but rather its the vertical draw you need to worry about. Both companies recommended that I not draw more than 2 feet in the vertical (distance from bottom of pickup tube to pump inlet), and I was well within that tolerance. I built a custom bracket that used existing holes in the frame to mount the pump, but there was no issue with drilling for a different bracket either. Mounted in this location, I found that there was ZERO pull down on fuel pressure, no matter what pump I used, no matter what horsepower level I was at. I've got customers sitting at 600 - 650 HP on straight diesel, and have been running strong for three or four years with the SAME pump in place. As a side note, this lift pump failure syndrome is not limited to ISB Dodges, but rather all VP44 ISB equipment. And the one thing they all have in common are those small banjo bolts. Lift pump location varies, and they all experience pre-mature failure. 2003 and up CP3 equipped trucks. The little pump that comes stock with CP3 equipped trucks is a pretty weak kneed little critter, but it is well suited to stock horsepower levels with only a little draw down on pressure at WOT throttle loads. I never did much experimentation at stock power levels, however I did install higher flow banjo bolts. As I expected, they didn't do much to affect flow, as the CP3 equipped trucks are already sitting at what I considered the upper limits powerwise for high flow banjos. I do however believe that the higher flowing banjo would help with early failures on stock powered pickup trucks. As soon as I started modifying the truck, I immediately replaced the lines with -8AN lines, but left the stock lift pump in place. I found that any kind of power increase over stock would immediately show a pressure decrease, even with the large lines installed. So I built an adapter, and stuffed a 14PSI 140 GPH Carter pump in the same location as we did with the VP44 equipped trucks. End result was ZERO draw down on pressure, even at the 500 HP level. I ran like this for a couple years, and never once had a burp out of the cheap Carter lift. So what can you do to your truck? If you plan on buying an aftermarket fuel system for your truck, skip by ALL the goofy pusher pumps. Complete waste of money, and you ruin the utility of your truck. The FASS system and AirDog mount back on the frame rail by the tank, and their additional filters hang BELOW the frame rails. To my way of thinking, this is extremely bad design. If you plan on modifying your truck past 300 HP, find yourself a system that replaces all the lines and banjos forward of the lift pump. If these lines are not replaced, you're wasting your money on everything else. Depending on your horsepower level, you may or may not have to replace the pump. If you want to build your own system (the cheapest route), contact Earls and get a set of their aluminum -6 adapters. They're available off the shelf. Then go to NAPA and buy some pushlock fittings and -6 diesel safe pushlock hose. Then buy a 140+ GPH pump from favorite manufacturer and mount it under the hood where its protected. I know I used -8 lines, but -6 would be lots right up to 500 HP. I hope this helps, and I hope that it saves some of you some money. Rod [/QUOTE]
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