Engine/Transmission (1998.5 - 2002) Why do LP's fail....??

[Behr]

A couple of questions regarding lift pumps and VP44.



I have been be hearing alot about defective lift pumps and was just curios to know if anyone knows just exactly what breaks down on these pumps. Is it just a question of "TIME"... . or are they just made "POORLY" ... . or could the "FUEL" have a bearing on their premature breakdown?



Also I don't quite understand why if the lift pump dies this would be a sure thing that the VP44 is about to die also.



I agree on the idea of having a fuel pressure gauge ... . but I would like to find out just why these pumps die pre-maturely. Do other vehicles have this problem... ?? Gas or Diesel... ??



Next question is just what percentage of LP's actually do fail. . ?



At this point I have not had any problems in regard to the fuel system.



Would love to hear any comments from the TDR Members on this...

 

[Ncostello]

From what I've seen and read here, and with my own failed lift pump, it seems there are multiple reasons.



For one the LP is an electric motor with brushs etc... and it is likely that some simply wear out or do not produce the power needed. DC electric motors do have a limited life span and eventually will give up. I have no idea how long our electric motors were designed to last. Its hard to gauge in miles. . probably better to look at hours on this issue.



On some pumps, the drive hub for the sliding vane impeller breaks. Thus the motor cannot transfer its power to the impeller and just spins uselessly. The impeller hub (metal) has a plastic insert in which the motor shaft inserts. As to why these break... . who knows? Bad plastic, junk jamming the vanes?



On some it is believed the rubber gasket under the pump top cover leaks air... whether the bolts come loose or the gasket just fails. The solution for this is often to turn the gasket over and retorque the hold down bolts.



And other times it is blamed on the internal bypass valve. It is a spring loaded ball valve (I think) that is set to bypass at some pressure above 15 or 16 psi. Some claim that the restrictions in the fuel lines between the lift pump and the injector pump is the cause of "overuse" of the valve... which then causes the spring to weaken over time and simply bypass fuel all the time. This kills the output pressure and volume. Maybe this is true, maybe it isn't but thats what I've read. It would make sense however if the valve was constantly bypassing fuel that the spring would weaken over time thus changing the set pressure at which it activates. This is hard to check because it requires destructive disassembly of the pump.



That is all I know and I'm sure there are better answers.

 

[Ncostello]

Forgot this too... the VP-44 is fuel lubricated. Thus if the LP dies you lose your ability to supply adequate fuel for cooling and lubrication. The engine runs OK because the VP44 is able to pull enough for that on its own. But not enough is supplied to protect the VP.



I've heard that the ISB requires a deliery rate of 0. 7 GPM (42 GPH) to run and keep everything cool and lubricated (. The stock LP was most likely chosen because it appeared able to do all of this according to the numbers.



The older injection pumps (P7100-12V engines 2nd Gen) were crankcase oil lubricated. If your lift pump went out you maybe lost power but the injector pump was mainly unharmed.

 

[Lsfarm]

Poor Location

Hello Behr, I suggest a search on 'lift pump' 'pusher pump' and 'fuel pressure'. Be prepared for a lot of reading,



The factory lift pump is being used in a location that is out of spec for the pump. The pump is designed [I believe these are the right specs] to pull fuel from a fuel source not further than three feet, and not lower than sixteen inches.



As installed in our trucks, the distance is around seven or eight feet, and the lift is between sixteen and twenty four inches. If the fuel tank is kept near full then the lift distance is minimized.



When a pusher pump is instaled just in front of the fuel tank, the combination of the two pumps seems to provide a reliable combination. I believe that just moving the factory pump down in front of the fuel tank has also provided a more reliable setup.



The problem is this: PUMPS LIKE TO PUSH, not to suck!! Positive pressure from gravity or a pusher pump will allow a pump to last as long as it can. Having to suck fuel from a low and distant fuel tank creates a 'made to fail' situation.



The fleet wide failure rate is unknown, most CTD owners either don't know or care about their lift-pump. Within the TDR I suspect the failure rate is around 50%.



For myself, the failure rate is 300% one at 15K, the next at 18K, and the third got weak a few thousand miles later, at which time I instaled a pusher pump and 12K later both are functioning fine.



If you don't have a fuel pressure gauge you have NO CLUE if your pump is healthy. Or if you have any fuel system issues. There are usually no indications when the lift pump fails, the VP44 just starts sucking fuel and starving for enough lubricaton and cooling and failure of the VP44 is the result, sometimes very soon, sometimes not for tens of thousands of miles later. Running with the fuel tank near empty will cause any failure to be sooner than later



I'm not willing to have my life disrupted by a failure that I can't fix on the roadside, so I have a full time fuel pressure guage, a pusher pump, and keep my fuel tank above 1/4 full usually above 1/2 full.



Most gasser vehicles have an in tank fuel pump, [they last virtually forever]. I don't know of a diesel application that has a submerged in-tank pump. I suspect the problem is the large variation of viscostiy that diesel fuel goes through with the temperature extremes our trucks opperate in.



Hope this helps, get a fuel pressure gauge installed!!



Greg L The Noise Nazi

 

[Behr]

I want to Thank you both Neil and Greg for the info.



Neil... in your post you mentioned on the older 12 Valve trucks the injection pump was lubricated by the crankcase oil. The 24 Valve is lubricated by the fuel itself. So it would seem one thing to look at would be some kind of extra lubrication to add to the fuel.



Question now is ... . the LP's on the 12 Valve just as prone to going south as the ones on the 24 Valve??



Greg - Question's for you ... . if I were to put a push pump down by the tank... would it be recommended to use an OEM - Cummins lift pump there and totally remove the existing LP from its present location... ?? If a push pump is installed... . will this void or affect DC factory warranty... ?? What is your opinion on having the push pump by the tank AND having the lift pump where it is now... ??



Does Cummins sell fuel pressure gauges... . or do I have to look for an after market source??

 

[Ncostello]

12V lift pumps are mechanical in nature and are driven off of a camshaft lobe. 24V engines do not have provisions for a mechanical pump, thus the electric one is onboard. They also seem to last much longer that the electric pumps. Totally different animal... much more reliable.



The use of a fuel additive is very recommended although Cummins states it is unnecessary. Low Sulfur fuel does little in the way of lubricating the VP-44's internals. Plus there are other benefits of additives such as lower smoke, increased cetane, and cold weather protection.



I use Stanadyne Performance Formula. Power Services is another available. Many out there.

 

[Behr]

Neil... I have been using off and on the Stanadyne additive... both the Performance and the Lubricity. I am also very careful only to buy fuel from brand names dealers... shell... Esso (Exxon) etc.



Now I did my first fuel filter change a few months ago... and I did notice that the fuel filter housing was quite clean. Did NOT see any kind of sediment in the bottom... and even the fuel that I drained from the housing prior to replaciing the filter look good and clean.



I know I should have changed the filter sooner... . but this was my first time... . did it at 18K miles. Was advised to change it every other oil change.



Do you have a push pump on your truck Neil... ?? or you just using the factory set up... ?

 

[Ncostello]

Actually I'm moving my stock lift pump down to the frame rail so it can push fuel more than it pulls fuel. Having it down at the same level (and closer) as the fuel itself is the biggest single improvement I believe. Plus it will make any future pump replacements 10x less messy and 10x faster because of the easy access to the pump. But it will be a single pump setup with larger hose (3/8") all the way around. I'm working on it currently.



Last night I was working on a custom frame bracket using my old lift pump as a guide for fitment and placement.

 

[Lsfarm]

Gauges and pusher pumps

Hi Behr, do a search on 'gauges' and you will have lots of info. Most Cummins shops don't sell aftermarket gauges, you can find many places to buy your gauges, PM or email me and I'll recommend a few.



The problem for me to remove the factory lift pump and mount it back in front of the fuel tank is that I still have only one pump, and if I had a warrantee issue, I would have to move it back to the factory position and this is a fair amount of work.



I added a 7psi high volume pusher pump and used this to pull fuel from the tank and push the fuel up to the factory pump. [look for Steve StLaurent's photos/post] I have proven to myself that fuel will flow through this pusher pump and allow the factory system to get fuel in the event the pusher pump or wiring dies. Some folks have provided bypass plumbing around the pusher pump. I don't feel this is needed, but I do carry a precut length of fuel hose with clamps to use to bypass the pusher pump if needed.



I'm sure that a dealer would try it's best to deny warrantee if the factory lift pump was removed and relocated. This is the main reason I have left the factory one in place. Adding a pusher pump is not a major project.



https://www.turbodieselregister.com/forums/showthread.php?s=&threadid=19767



Greg L The Noise Nazi

 

[JR2]

Ncostello (and anyone else thinking about moving the stock pump) - do not remove the bracket for the stock lift pump from the side of the engine. It actually covers a hole in the block where a mechanical pump would go. . The 24v trucks have a hole for the mechanical 12v pump, just no lobe on the camshaft. . that is unless you have an aftermarket cam shaft but that is another subject. .



I moved my stock pump to the frame rail back by the tank. Used an L bracket from Home Depot (galvanized bracket). It cost around $3 and all I had to do was drill a couple of extra hole s in it.





John

 

[Whitmore]

Re: Poor Location

Great job Greg,



The factory lift pump is being used in a location that is out of spec for the pump. The pump is designed [I believe these are the right specs] to pull fuel from a fuel source not further than three feet, and not lower than sixteen inches.



As installed in our trucks, the distance is around seven or eight feet, and the lift is between sixteen and twenty four inches. If the fuel tank is kept near full then the lift distance is minimized.



The problem is this: PUMPS LIKE TO PUSH, not to suck!! Positive pressure from gravity or a pusher pump will allow a pump to last as long as it can. Having to suck fuel from a low and distant fuel tank creates a 'made to fail' situation. sometimes not for tens of thousands of miles later.



Greg L The Noise Nazi



Greg is absoluty correct in the above statement, I firmly believe that the OEM lift pump is the best pump available to us at this time but also think that the setup is the problem, as Greg states NO pump likes to pull a vacumn but prefers a positive head pressure, the OEM setup is the problem, the pump is on a constant vacumn from pulling up to 2 feet and from up to 8 feet away, there is not a pump on the market that will survive this kind of application. I am sure I will catch some flack over this but IMHO a pusher pump is only a bandaid at best and with 2 pumps you then have twice the chance of failure. With that said once again there is only one fix for this, You MUST install your L/P lower than your supplied fuel source and the less line between the fuel and the pump the better, You MUST also have addequate delivery lines to and from the pump, at least 1/2" line to be safe, some of you may comment that the inlet and outlet of the pump are like 3/8" and that is true but trust me here larger line is necessary in order to supply the least resistance as possible.



Here is what I have done to correct my OEM fuel delivery system. I purchased an auxillary inbed fuel tank, this is my MAIN supply to my delivery pump ( no longer a lift pump ) I have installed a ball valve at the bottom of the tank for maintenance purposes and 1/2" line to the pump, 1/2" line to the OEM filter housing in its original location and 1/2" line from the filter to the VP-44... ... ... ... ... ... ... ... ..... RESULTS ARE I now idle at 15 psi of pressure and cruze 75 mph at 15 psi!!! and at wot I can only pull it down to 12 psi!!! As far as fuel usage from my Cummins I have 275 injectors and a comp box, the above stated readings are with the comp on 5x5. I now use my OEM fuel tank as a storage and transfer tank, I use a small 40 dollar pump for this task, something interesting here is at first I used the oem line from the OEM tank to the aux tank and it took about 30 minutes to transfer its contents up to the aux tank, I didnt like that so I installed 1/2" line and now I can transfer in 13 minutes!!! That tells me alot about fuel delivery lines because the transfer pump and its location didnot change, I simply reduced the resistance of the lines.



I really wish I had a amp load reading from the pump from before and after this mod. I know it is less because the pump is not working near as hard now.



OK OK, I know that this setup is not for everyone but the same logic can be applied to this concept on the OEM tank as a main fuel delivery system. It is not very expensive and will help alot.



Good Luck, Kevin

 

[Ncostello]

Thanx JR2. . I remembered that from posts long ago. I was going to make a flat cover plate to replace the bracket. But my pump bracket will be a totally custom deal with some shielding plates around the pump to protect from debris and spray. My goal is to somehow make it look like its factory installed... yet outperform the stock system.

 

[Ncostello]

Here is one for the pro's of LP conversions. Do you think the newer version of the fuel canister is better in the overall picture of fuel delivery?? It certainly is easier to change the filter on the newer one.



By looking at them, it seems the fuel comes in towards the top then flows downward and out the bottom level. This outlet location is more in line with the VP and makes for easier plumbing.



On my 99, the fuel enters the top, flows down through the filter then has to make a trip back out the top then back down to the VP. Seems like one more "big" turn for the fuel path to follow. I realize the difference may be slight if any but there should still be a difference.



I was wanting to replace my canister with the newer style but the cost is kinda prohibitive. The complete setup is expensive from dodge. I was also considering moving the stock canister I have downwards to lessen the height the LP has to pump to. But then filter changes become more difficult.

 

[Behr]

Kevin... ... thank you very much for your input.



I guess my concern as I said earlier in the thread is what affect any kind of mods will have on my warranty. Dealers I am sure are like insurance companies... . if they can find a way out of not having to pay... . they will.



I like the idea of having the pump down close to the source... . or even just a bit lower than the tank... . but also the idea of using increased line size sounds good to.



I don't why DC has not moved the pump back closer to the tank... . surely they have had a couple of years to see the evidence.



I am not able to put an inbed tank on my truck... . so will have to stick with just the factory one.



I will phone cummins up here and get a price on a new lift pump... . then when I am ready will install it down by the tank. I see from other posts they run about $150. 00 US so will be interesting to see what they charge in Canada...

 

[Mtngoat]

Isn't it incredible that owners of (fairly) new trucks have to carry an extra pump and tools with them in case the pump goes out, or resort to adding additional pumps to keep thier trucks running? Does Dodge not see the problem?? Surely someone has taken them to task for an answer!! Does anybody know what Dodge's response is or was???



Robin

 

[Mtngoat]

Isn't it incredible that owners of (fairly) new trucks have to carry an extra pump and tools with them in case the pump goes out, or resort to adding additional pumps to keep thier trucks running? Does Dodge not see the problem?? Surely someone has taken them to task for an answer!! Does anybody know what Dodge's response is or was???



Robin

 

[Mtngoat]

Isn't it incredible that owners of (fairly) new trucks have to carry an extra pump and tools with them in case the pump goes out, or resort to adding additional pumps to keep thier trucks running? Does Dodge not see the problem?? Surely someone has taken them to task for an answer!! Does anybody know what Dodge's response is or was???



Robin

 

[WadePatton]

DC will not admit the problem. They rarely have LP's in stock and will generally take 2 days to diagnose the low pressure CLEARLY indicated on your gauge.



Which is REALLLLLY stupid. The more LP's they can replace--the fewer VP44's they HAVE to replace.



It's a pity that for the unknowing consumer (most of them) that DC is tarnishing the Cummins name with this sort of failure.



I'm moving my LP to the back.

 

[krs]

I never see a mention of any filtration installed before a liftpump though I know that some members have added them in one form or another. DC does not include such a filter either.



If you get a new Carter fuel pump in it's box there will be a sheet of instructions for it's use. Amongst those is a very clear warning that using the pump without prior filtration will void the pump warranty.



I think that this points to a main cause of liftpump failure. The pump, including the 7 psi Carter often selected as a pusher can be destroyed by fuel contaminants and tank debri.

 

[Mad Bomber]

lift pump

I had the 2 LP system and lost the stock one at 36K. This weekend I just put in the PE 4200. I know that many poeple are good luck with it 20K. We shall see. Eric