I thought I'd post about my "outlier" of a lift pump.

Lift pump durability is one of the most oft-posted topics of discussion on this or any other board where VP44-equipped Dodges are discussed.

Before I offer my comments, may I offer to you some reasons to consider my opinion?
-- I have been the one owner of this truck since the day it was sold in August of 2002 as a late-production '02 model.
-- I have been around B-series engines and this Cummins/Dodge obsession since the year before the purchase of my truck.
-- Though my job at Cummins has changed, I have experience with fuel system engineering at Cummins-- specifically with the Federal-Mogul pump used on our very trucks. That experience was testing the reliability and durability of the F-M pump for the 2010 ISX. I have seen the Federal Mogul engineer presentations. I have torn these pumps apart and seen exactly how they fail and why. The poor performance in testing is why the 2010 and newer ISX doesn't have the FM pump any more!


The FM pump is a sliding vane design that primarily fails one of a couple ways:
1) The wires to the brushes fail from vibration-related fatigue
2) The brushes wear irregularly on the commutator (due to vibration) and induce either brush failure or shaft/bearing failure.
3) The sliding vanes gall the inside of pump (the "wiping" surface)
4) The vanes gall in the pump rotor itself will no longer "slide" out to make contact with the "wiping surface."

There are also other, far less common failures related to the cheap zinc housing of the pump and how poorly suited it is to the design of a robust pump, there's also the tendency towards momentary spurts of excessive current draw that can cause motor failure.

But by and large, there's one single, overwhelming cause of LP failure in my opinion: vibration.

Almost without exception, pumps that are required to have a long life are Gerotors, Gear Pumps or (slightly less durable) roller vane pumps. Each of these designs is much more robust to vibration.

In hindsight, a very cheap sliding vane pump bolted directly to a high-vibration engine is not a recipe for reliability. I don't know a single person at Cummins who had experience on the engine program at the time who would claim this was a robust solution.

My understanding is that Chrysler insisted on avoiding the higher cost of a more robust pump.



Still, IF THE VIBRATION IS REDUCED below a certain threshold, these low-cost FM pumps can, in fact, leave reasonably long lives and perform acceptably well.

I believe my truck's original LP is still going because it has had less vibration throughout its life. This is my opinion, not empirical fact. It is also a single, solitary data point-- an anecdote. Extrapolate at your own risk.


Why has my truck had less vibration?

I put in aftermarket injectors when the truck only had 11,000 miles on it. The Diesel Dynamics (remember them??) Stage 2 injectors were advertised as a 90hp gain for the HO trucks. Immediately I noticed that the truck had far less "clatter" at idle. The combustion pressure rise was not as fast-- probably because the atomization of the extrude-honed nozzles was inferior to the stock injectors.

I ran these injectors for 3 years until I moved up to a larger "Mach 4" injector from Don Morrisson's F1 Diesel. I continue with these injectors today-- they have pulled daily driver duty for almost eight years now with remarkable aplomb (including an unplugged start a few weeks ago at -15F).

Both the DD injector and then the F1 injectors made the engine quieter than it was before each was installed. The continued trend of larger injectors with lower injector pressure reduced engine noise by slowing down the combustion event.

On a VP44 truck, a higher flowing injector will always lead to lower peak injection pressures. Having the pop pressure set towards the lower end (as most aftermarket injectors do-- the F1s are set just under 200 bar while the the factory spec is 207 bar) will slightly exaggerate this, but pop pressure doesn't determine peak injector pressure.

Injection pressure on a PLN system builds up because the pump is flowing more fuel than the open nozzle will accept at the given pressure. The pressure in the injector rises -- even after the injector is open and spraying-- until the flow rate into it and the flow rate out of the injector achieve equilibrium. Thus, a higher flow injector achieves this equilibrium at a lower injector pressure.

When you install larger injectors, you can drop peak injection pressure rather quickly. Anyone who's removed the thumb from the end of the hose knows this intuitively.


There was a time when relocation of the lift pump was a popular reliability enhancement, and I think failures in those cases were pretty rare. In my opinion, the reduced vibration-- not the reduce pump lift-- was the main reason.


While transfer pump reliability problems are mostly relegated to older trucks like mine and those that came a little later, I hope this helps those of you who may be on the fence as to how to improve pump reliability.

 

Nice write-up HOHN.

I lost my original lp and had the dealer installed in tank unit on warranty...It gave 10 psi at idle and dropped to around zero if I wailed on it. Until I could afford a better pump I just avoided WOT applications. I noticed it started to slip to 8 psi and changed the filter to regain 10 but didn't see it so I ordered a FASS and mounted it just outside the tank on the bed rail and now have a steady 16 psi at idle and not below 9 ish at WOT.

Congrats on your original lp. Any thoughts regarding push/pull operations? Are you planning on replacing it soon, or waiting for it to fail?

 

Justin, it's good to see you posting again but my experience has been different with these lift pumps. Mine died early on and now have an older Raptor on the frame just in front of the rear tire and it does well. My bud's '99 used the OEM for years and I kept telling him he needed a pressure gauge. He finally stopped by with the rig and I suggested we go over to Eric's (Vulcan) and check his fuel pressure and put a gauge in. I pulled the plug on top of the filter and guess what??? No start because no fuel being pumped. Who knows how long. That was several years ago and it is still on the original IP. We ended up stuck @ Erics and put a replacement pump on there. And he spent a whole bunch more $$$ than just a gauge would cost but at least he was not on the side of the road or at the mercy of somebody servicing his filter and not knowing what was really going on. He sure wouldn't have known even though I had been warning this would happen for several or more years.

I used these pumps on gassers back in the 60's and they failed just as badly or worse. I took one apart then and now and they appeared no different now than back then. MHO?? They were junk then and are junk now!!

 

I agree, most people's experience with these questionable pumps has been very different than mine.

I'm not trying to say the pump is a good one at all. I'm trying to say that I think I know why they generally fare poorly and why I think my case may show how reduced vibration can help (but not sure) the LP problems.

I assure you that if my LP does die, as indeed it inevitably must, I will NOT be using a factory replacement.

I have a couple Walbro Solenoid pumps that are rated 10k hours plus reliability. They just don't have very good flow curves, so I'd have to use two of them in parallel.


The pumps failing on a gasser is not that surprising since the sliding vane has very high friction in gasoline.

 

I always wondered how vane pumps in gasoline lasted as long as they do...

I can see the vane style getting off kilter by engine vibes and biting the housing over and over enough to finally fail.

I'm proud of your stock pump. My FASS is supposed to go 50K hours...we'll see.

 

Interesting writeup HOHN. I enjoy reading your material because of the information you include actually pertains.

In regards to overall OEM lift pump reliability, over the past decade or so I've read a few different approaches, opinions, and reasons as to what the high rate of failure for these pumps.

In short, because I'm not in the mood to type for hours, these are the basics I remember.....

1) the pump mounted to the engine causes excess vibration which basically vibrates the pump to failure. Something along the lines of what you just described and people have found that moving the pump helps with reliability.

2) the pump is mounted to the motor which is sitting slightly higher than the fuel tank and the pump is then forced to "suck" fuel rather than push fuel. Again, moving the pumps to the frame has proven to be better than on the block. So obviously pumps like to push more than work under a vacuum but putting that rule aside since most pumps will suck just as much as push, these pumps have internal pressure bypass systems built in them which consist of merely a checkball and spring. At approximately 15 psi the spring and ball allows internal pressure to bypass but because of poor pump housing material and/or poor design all together the ball eventually burrows itself into the housing. Over time the farther and farther the ball makes its way, the less pressure the pump can make since the ball is remaining in a permanent state of "bypass" keeping fuel from pumping.

3) the pump vain is made of plastic and is mounted to the metal pump shaft via an adhesive material. This "glue" can deteriorate and/or from vibration, working under a vacuum, or because of changes in the diesel fuels chemical structure attack the glue and.....also running caustic biofuel. None are listed as the specific and one and only cause for the glue to fail but in point, the impeller detaches from the shaft and the motor free spins but no pumping.

Now in saying all that I am willing to bet that ALL failures happen and what one person finds to be the reason may or may not be the reason for another. Or.....they're all wrong. Either way, its not a pump I'd use anymore on these engines.

 

I thought the pump would probably work better with diesel than gas because of the greater natural lubricity of diesel. That has proven to not be the case for whatever reason whether it is because of vibration, pump location or anything else one might think of.

 

I took my original lift pump out when it's pressure reduced to 14psi idle and 7psi WOT.

After trying other pumps, including the Carter 4601HP that I installed on the frame rail and lasted 7 years, I'm still searching.
Last summer on the way to the local round track races, the one in service at that time failed/0psi.
I took the spare from under the seat, the genuine original pump, plugged it in and got the 14psi idle and 7psi WOT just the same....lol
Made it to the races on time too.

 

i wish i had 14/7 on my setup...i have the campaign pump on the frame with another campaign pump in line on the frame as a backup.
http://s276.photobucket.com/user/joh...ml?sort=3&o=80

 

12 years and 108,000 miles on my original lift pump but I drive like an old man.....