Anatomy of a Lift Pump - A

[Gary - K7GLD]

Newcomers - and some older owners don't know exactly what a Lift Pump (LP) is, what it does, and what makes it tick - hopefully this will help towards a better understanding. Here's what a LP looks like:



This is approximately what the LP (Lift Pump) looks like as installed at the driver-side rear area of the Cummins in our trucks. 3 bolts attach the pump to a bracket on the engine, there is an in and out fuel line, and either a plug for power attachment to power the pump like this one, or on older styles, the wiring was attached to posts on the bottom of the motor. That style was eventually discontinued due to salt and other contaminents damaging connections and causing LP failures.

Below we see the internals of the actual pump section with the cover removed. You can see the vanes - this is a vane-type pump, and the rotor that holds them as they rotate inside the walls of the pump housing. This is the ONLY part of the pump that can be disassembled for any sort of cleaning or service.




Here below, is a closer look at the disassembled pump rotor, with the vanes laying in front - those vanes simply float in their respective slots, and press against the walls of the pump by the rotational force of the pump rotor. Occasionally, those vanes might become sticky and not float freely in their slots, reducing or stopping fuel flow.

Inside the pump housing can be seen the end of the pump motor shaft with the milled end that engages the matching slot of the nylon insert pressed into the pump rotor. Occasionally, the nylon shaft coupling will fail, and fuel flow will stop, even though the motor will still spin. No known means or replacements are available to replace a damaged one - so the pump usually must be replaced when this occurs.

Also seen, is the fine stainless steel mesh filter strip formed around the outside of the pump cavity to provide filtering of any coarser trash that might enter that housing



(MORE below.)

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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.

[Gary - K7GLD]

(continued)

Below, we see the disassembled motor section on the left, next to the pump section on the right - as previously mentioned, the only way to disassemble the motor is to cut it open, which totally destroys it for further use. In the housing seen above the motor armature, on the left side, is the spring-loaded ball check valve used to regulate fuel pressure.

This is a VERY common failure point, when either the spring fails, or the ball beats the seat out of the housing, allowing fuel to merely circulate between the pump and motor, with none or little actually getting to the VP-44 injection pump. And as can be seen fuel actually does flow thru the motor as well as the pump inself in normal operation.



Here's a closeup shot down the inside of the motor, showing the bottom bearing and the green circuit board with electronics to eliminate static radiation in normal operation - also note the excellent condition of the brushes and other components. This pump had 110,000 miles on it when removed from service, and that only as a maintenance procedure, since it was still operating perfectly!



SO, there you have the anatomy of a LP, how it works, and some of the more common failure points!

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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.

[Gary - K7GLD]

Some additional issues as they apply to the stock LP. I have personally had *2* instances where the power plug to the LP became erratic, or lost connection completely, causing the engine to nearly die of fuel starvation - all that was needed to correct the situation, was to re-seat the power plug, and normal LP operation was restored.

A second area to keep watch on, is the push-on type hose connections to/from the LP - they have been noted for air leakage, especially after a LP has been changed and the original factory seal broken. Added to this, is the occasional tendency for fuel line splits, often right down inside the fuel tank where they can't be seen - those breaks usually reveal themselves when poor truck operation regularly occurs when the fuel level gets down to a point below where the line is split and leaking.

And finally, one of the best upgrades to the stock LP. is the addition of what is referred to as a "Pusher" pump - usually a Carter 4600 pump nearly identical in appearance to the stock LP - which is also a Carter item.

The added pusher pump enhances and assists operation of the stock LP, and is especially beneficial when power mods to the Cummins are added, and require a more abundant and reliable fuel flow.

Another thread will describe that mod...

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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.

[Monster Truck]

this is off a 24v im guessing?

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Dads: 99 2500 Ext Cab Longbed 4X4 3.55s CTD, 5'', 47re, BHAF Outerwear Heat Sheild, Turnbuckle Wastgate, Fuel Pressure, Sucnoast Tripple Disk TC with custom vb work.
Mine: 95 Ext Cab SLT, Loaded, 5spd, 3.54s, Leveled 5'' Lift 35'' Toyos, 4'' Straight into a 5'' bed kit with 6'' Mitres, Super B 57/66/14, Stage 2 Sticks, 3GSK, #60 Valve Springs, Stage 2 clutch, Custom Intake, Plateless, Boost and EGT on the pillar.

Originally Posted by Monster Truck

this is off a 24v im guessing?

Yes George its from a 24v.This pump is all the same on years 98.5-02.....the 12 valvers are mechanical


There would be a different lift pump on 03 and up vintages

[Monster Truck]

so when you get anew one is just swap and go right?

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Dads: 99 2500 Ext Cab Longbed 4X4 3.55s CTD, 5'', 47re, BHAF Outerwear Heat Sheild, Turnbuckle Wastgate, Fuel Pressure, Sucnoast Tripple Disk TC with custom vb work.
Mine: 95 Ext Cab SLT, Loaded, 5spd, 3.54s, Leveled 5'' Lift 35'' Toyos, 4'' Straight into a 5'' bed kit with 6'' Mitres, Super B 57/66/14, Stage 2 Sticks, 3GSK, #60 Valve Springs, Stage 2 clutch, Custom Intake, Plateless, Boost and EGT on the pillar.

Originally Posted by Monster Truck

so when you get anew one is just swap and go right?

Yep its just swap and go but ya hafta prime the system just like when ya change a fuel filter.

By the way the OEM pump is non servicable, Gary had to cut it open to show us what was in there.........I have disected 3 of them and they are cheap

[Dr. Evil]

GREAT info Gary !

[Dr. Evil]

Originally Posted by Whitmore

I have disected 3 of them and they are cheap

More correctly, they are cheaply made...

[Gary - K7GLD]

Originally Posted by Dr. Evil

More correctly, they are cheaply made...

WELL, actually, they are pretty typical of ALL pumps in this class - and even the high-priced aftermarket alternatives seemingly have most of the same issues as the DC LP's do - in spite of hype and hoopla to claim otherwise.

If you inspect the stock LP closely, what could be realistically done to make them less "cheap"? All I can see, is better bearings - rollers perhaps, but other than that, what? The armature is as well built as any you're likely to compare against - and the field magnets are also quite adequate and typical of this type motor. The brushes and holders are fine, and after over 100,000 miles on the one shown, the brushes themselves were less than 1/3 worn. The pressure relief valves occasionall are an issue, but are typical of aftermarket valves costing more than the whole LP itself - biggest problem with the stock LP doesn't seem as much to be the PUMP design or construction, but where it is INSTALLED in the fuel system!

In reality, the motor sections used in these pumps are VERY typical of the heater and windshield wiper motors used in our trucks in most mechanical areas.

As to the pump section, all moving and mating parts are stainless steel - and again, the one I took apart showed minimal wear - the only evident weakness being the nylon shaft coupler between the pump and motor shaft.

Sure, you can pay 4-5 times as much for a FASS, or other pumps - and guess what, THEY fail pretty regularly too!

__________________
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.

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Last edited by Gary - K7GLD : 03-26-2006 at 09:42 AM.

So what is everyone running for a pusher pump? How many PSI are you holding?

Andy

[Dr. Evil]

Originally Posted by Gary - K7GLD

Sure, you can pay 4-5 times as much for a FASS, or other pumps - and guess what, THEY fail pretty regularly too!

I dunno about that...The Pumps the FASS kits use are pretty stout (especially the ones with the sealed brushes)...although I must admit ive never seen one that was cut open.

But, and this is a big But, they are $$