Engine/Transmission (1998.5 - 2002) Lift pump thoughts.........

[Big White Beast]

Having an 01 I am acutely aware of the lift pump problems and have been following most threads to see what fixes work and what don't.



Most people it seems haven't autopsied their pumps to see what destroyed them. I'd be curious as to what the most common problem is. I know the lift pump has a long way to pull from the tank but it seems even some of the after market ones by the tank are failing. I have also read that people destroy their gauge sender units from the VP-44 hammering. I could actually hear it loud and clear in the cab when I had my mechanical fuel pressure gauge installed. Is diesel like water, where it won't compress hence sending the shock all the way back?



Here's my thought, if this hammering is part of what's destroying the pumps would it be feasable to put some kind of check valve in after the pump to try and save it? I know with the constant flow of the lift pump a check valve probably wouldn't be able to do it's job. I don't think a snubber would allow enough fuel flow. Possibly something like a water hammer protector, where it traps air that can be compressed?



Am I way off base here? I just think there has to be a way of saving the pumps from self destruction.



Any people out there more versed in fluid dynamics that could think of a way to stop the hammering from coming back up the system?



Anyway that's my thoughts, I would love to hear yours, good, bad or indifferent.



Garrett

 

[lsenus]

Wow. I've read that every one isolates thier guages with rubber hoses of some sort to dampen the pump pulse effect, but the lift pumps have the steel banjo lines connected. Hmmmmmmm.

Has anyone who installed the Aeroquip hose and fittings had a pump failure? Also, what is the max flow rate of the VP44? Can the lift pumps keep up with it?

Just thinking again.

 

[M Evan]

That is very interesting thoughts. Maybe just replace hard line from filter to inj. pump with flex line will give lift pump longer life. Maybe mount lift pump from engine to the body and connect with flex line, but still leave on front will help to. Ohh, I love this TDR board, always something new every day to think about.

M

 

[JPittman]

M Evan

On my '99, there is a rubber hose in the middle of the hard fuel line from the filter to the injection pump. Sounds like they have eliminated this section of rubber hose on the newer models. Probably did it to save $$, but what could 2 clamps and 6" of hose cost?

 

[M Evan]

JPittman, that is interesting, did you change your pump already ? And if so , after how many miles ?

M

 

[JPittman]

M Evan,

Original pump (knock on wood) with 31,000 miles.

 

[Big White Beast]

Interesting......

So the 99's and possibly the 00's had that rubber hose in line. Because it does seem that the pumps you hear about the most are on the 01's. Any other ideas out there??



Will a rubber hose providing enough relief from the hammering?



Garrett

 

[15w40]

If you do a search in the archives on lift pumps, there are lots of ideas on how to keep lift pumps alive. I believe you are correct in thinking that the pressure pulsations will kill the pump after about 50K miles (or 1200 hours) but that is only one mechanism of failure. Both the rotary vane pump at the input of the VP44 and the rotary vane lift pump itself will cause pulsations. These pressure pulsations will cause the lift pump, spring loaded “spill-over” valve to fail. This will show up as low pressure and fluctuating pressure readings.



Another way these lift pumps fail is when the plastic coupling between the electric motor and rotary vane pump break. Pressure will drop to zero. Reports have been made here where people have changed the fuel filter and are unable to refill the canister using the lift pump. This failure mechanism may be caused by a piece of trash jamming the rotary vane pump, but this is only a guess.



As long as we are stuck with the Carter lift pump, I think the best thing you can do is move it back to the tank. By getting it further away from the VP44, using a rubber fuel line, some of the pressure pulsations will be soaked up. This also makes it easier on the pump. The only problem with the move is if you operate in frigid weather. There is a chance that the fuel can jell at the pump without the benefit of the engine heat, but a good anti-jell should solve that problem.



I know I will get flamed for the next statement, but unless you are making some serious horsepower, adding a pusher pump will not help. (In my humble opinion)

 

[w-cummins]

Originally posted by 15w40

The only problem with the move is if you operate in frigid weather. There is a chance that the fuel can jell at the pump without the benefit of the engine heat, but a good anti-jell should solve that problem.

Well it seems to me that if it's cold enough to gel the fuel in the pump back by the tank, it's also cold enough to gell the the fuel in the line from the tank to the pump, the fuel tank, and the COLD pump mounted on the engine when you first start it... .



William.....

 

[TPlasek]

When you moved the stock pump back by the tank, did you change to larger "rubber" fuel lines or just use the stock ones??? Also when moving your stock pump from front to back did you see a drop in fuel psi at the VP44??? I just put a new pump on this weekend after 80 k. I will be taking my old one apart to see what went wrong. The electric motor still runs. It will build 7 psi at first and then quicky go to 0 after the engine starts. If the pulsating fuel "hammer" is causing the relief valve to fail, the futher away from the VP44 and the rubber hose should help. If it is the vane pump that has failed, the closer to the tank the better off it would be. It is much easier to push fluid the suck. Plus, air bubbles and cavitation are bad for a vane pump.



Other then fuel pressure at the VP44, anyone with some thoughts on why I should keep the pump in it stock location?

 

[lsenus]

If you move the pump, and the VP44 dies, the dealer will most likely give you a hard time about the warranty.

My FP died Weds. of last week. I put in a new FP, got pressure at the VP44, but would not start. I tried everything, see my thread:

https://www.turbodieselregister.com/forums/showthread.php?threadid=49319



I put the dead FP back in, towed it to the dealer who said the FP was dead, replaced it under warranty at 89000mi only to discover the VP44 was dead.



That is now being replaced under warranty.

 

[Lsfarm]

Help What?

15w-40, did you read the post above and read the link? Isenus has a totally stock truck, and the lift pump died during normal use, and killed the VP44.

In what way would a good functioning pusher pump feeding the stock lift pump [so that it didn't fail] not be a help to prevent the above failure of the Vp44??



History has proven that the factory lift pump is very short lived in stock trucks AND modified trucks. The VP 44 is very easily damaged by lack of cooling and lubrication when the lift pump dies.



Every CTD needs a fuel pressure gauge and a pusher pump or the factory pump moved to the front of the tank. At least then the pump will be doing it's job within the manufacturers specifications.



I'm on my third factory lift pump at 21K.



Greg L

 

[lsenus]

I've been looking for a 30 psi fuel pressure gauge. The 0-15 's don't read high enough, and the 0-100 's scale is too small for our pump pressures.

I found some marine sites and some info about diesel fule line pulsation dampeners. It seems that in order to get good flow readings, pulsation dampeners must be used to isolate the injector pump. Hmmmmmmmmm.



VP44=Lift Pump slayer?????



http://www.floscan.com/html/index.asp



then go to the Pulsation dampeners link for a diagram.

 

[Big White Beast]

Well, I called floscan.......

Their tech said that it probably wouldn't work for our application. It's a shame too because it looked like it would be simple to plumb in.



They said it is just a hammer arrestor like a water pipe one. It would have to be on the highest point of the fuel system also. Close to the hood for us. It relies on air in the system to dampen the shock. Mounting it on the feed side of the lift pump would eventually drive the air out according to their tech. He couldn't estimate on how long but figured no more than a couple of days. You could bleed it down every few days but that doesn't seem practical.



He mentioned a low pressure hydraulic accumulator. Have to look into that.



Garrett

 

[lsenus]

Garrett,

I'll also look into it as well. ... two heads are better than one right??



So far I've only found 2 manufs. that make the 2-30 psi range fuel pressure gauges, but both are black dials. I would like to get the white or silver face dial if possible, similar to the Autometer Ultra-Lite series. I'll keep looking.

 

[15w40]

Lsfarm, It is possible for the pusher pump to keep the VP44 alive by supplying some positive pressure. I don’t believe the pusher pump will help keep the lift pump alive. (I knew my statement about the pusher pump would cause some agitation. ) In my opinion the main cause of failure of the lift pump is the spring in the spillover valve that regulates the maximum lift pump pressure.



I have read posts that Carter has stated their pump were not designed to be more than a few feet from the fuel supply. The problem I have with this is; why this is true? If the pump is sucking fuel through a long, small diameter hose, there will be a vacuum at the input to the pump and as the level in the fuel tank falls the vacuum will be larger as the pump tries to “lift” the fuel a greater distance. If the vacuum is large enough the fuel will cause cavitations and erode the rotary vane pump and the volute. The rotary vane pump in my dead pump was in perfect condition and others have reported the same. This seems to rules out that there was too much vacuum when the pump is in the stock location. I do agree that a vacuum on the input side of the lift pump will reduce the pressure on the output side of the pump and the VP44 may die. If you arte making large amounts of horsepower it is better mounted near the tank.



Inside the lift pump is a constant volume vane pump. A spring-loaded spillover valve sets the output pressure internal to the pump. For a good lift pump, the pressure is about 15 PSI with no vacuum at its input port. If there is a -5PSI vacuum at the input the output will now be only 10 PSI. (I know vacuum is measured in inches of mercury or inches of water but to keep it simple I’ll use negative PSI. ) The difference between the input pressure or vacuum and the output pressure remains at 15 PSI for a good pump. Now if I add a 7 PSI pusher pump back at the tank to feed the lift pump, the output pressure will be about 7 + 15 PSI or about 22 PSI. (I am ignoring restrictions in the banjo fittings and fuel hoses. ) In this case the lift pump is still bypassing excess fuel through the spillover valve at the same rate. The spring is still flexing at about 330 cycles per second and fatiguing. This number comes from the 5000 RPM lift pump speed and the 4 vanes of the rotary pump causing a pulse as they pass the input port internal to the lift pump. It does not matter what the pressure is on the input side of the lift pump is. It is working just as hard.



The spillover valve will remain closed if the VP44 is sucking enough fuel to reduce the output pressure of the lift pump below the spillover valve cracking pressure and the spring will not fatigue. This would require driving at WOT a lot.

 

[Steve St.Laurent]

If that's the case 15w40 (and believe me I'm not trying to flame you or anything) then how do you explain my experience where between 28,000 and 60,000 miles I went through 4 lift pumps (bought the truck used with 28,000 miles). At that point I replaced the stock lift pump with a new one (not the most current variation, btw) and added a carter pusher pump back at the tank and 45,000 miles later I'm still running great. On top of that not a single one of the stock replacement pumps would maintain 8 psi at WOT (granted I'm not stock, but am hardly running a hot rod compared to many around here) yet with the pusher pump I never go below 16 psi? This experience is common with many of my friends that have added pusher pumps - they went through stock ones like underwear, then added the pusher pump and haven't had a failure since.

 

[15w40]

Steve, I kind of expected a response from you about pusher pumps and I am glad it is working out for you. But you have to understand that being an engineer and analyzing failure mechanisms is something I have been doing for many years. I try to base my theories on factual data coming from measurements. Is your situation proof of a fix? If it was shown that adding a pusher pump reduced the pressure pulses then I would believe it, but it also may just be the luck of the draw. Have you determined what mechanism caused the 4 lift pumps to fail before adding the pusher pump? I would like to tear them apart and see.



The new lift pump on your truck has seen about 45K. Although this is longer than the previous pumps that mileage is not unusual for some of the later designed pumps.



One last thought. It might be that the higher pressure, 16 PSI +, is keeping the spillover valve in the VP44 open so that fuel pulses generated by the rotary vane pump inside the VP44 is relieved and not getting back to the lift pump. If that is the case, then you may be correct, but without the measurement details who can tell. Leaving off the pusher pump and adding a hydraulic accumulator between the lift pump and VP44 could have the same or better results. I am currently using an air filled. 1-quart poly canister connected to my fuel filter to soak up the pressure pulses. It has been 20K miles since I added it with my new lift pump. So far my pressure never gets below 10 PSI and the pulsations are gone. Is this the fix? It will be a while before I know, but I would not dare claim victory.

 

[BK]

I have a bone stock engine. My lift pump is dying. 8psi @ idle, 3. 8psi@3K and 2psi@WOT.



My truck is a 99, 27K miles, just days before my 36month warranty expires.



Been changing my fuel filter every year, once a year.



I have the rubber hose in my 99, between the fuel filter and LP.

But I would imagine that the fuel filter would be a great buffer from the effects of the '44. I could imagine the vibration of the engine could contribute, beside the pump working it'self to death from drawing against a vacum more than it should.

But as someone else mentioned, we've heard about LP failure from those who put them on the frame rail... far removed from the '44 hamering and the engine's bad vibs.



After this, I'll buy a LP to keep in the truck. But as someone else mentioned earlier... I'm worried about moving a pump to the frame rail and having to fight for a warranty on the '44... . since my stealer SUCKS on warranty work.



As an engineer, I too would love to do an autopsy on my LP. But I doubt my stealer would even let me touch the one they take out.

 

[Whitmore]

15-40, I couldnt agree with this theroy more

One last thought. It might be that the higher pressure, 16 PSI +, is keeping the spillover valve in the VP44 open so that fuel pulses generated by the rotary vane pump inside the VP44 is relieved and not getting back to the lift pump.

Also from a stock set up I truely believe that the spillback spring on the check is getting fatigued and failing or opening at a lesser pressure thus we then show less psi at the VP-44 , if that were true than in theory the stock carter pump is doing just fine but the failure is in the spillback, so if we could measure the total gph from the output of the pump as well as the spillback too it would prove the pump to be fine.



One thing that I know thru my years as a process operator is that flow does not dictate pressure , in other words pressure is didtated by resistance to flow or what I would call back pressure. If this is true than what we need to be concerned with for the health of our VP-44 is not pressure but flow, the only reason we currently use pressure is because it is easy to measure, IMHO if we could measure the flow from the spillback or unused fuel from the VP-44 than we are talking apples!( hence... cooling and lubricity from that flow)



I think the best setup we could ever get would be a pump in the tank, I know I know alot of you hate the thought of it but think of this . the pump would always have a positive pressure and and the huge on in my book is no vaccumn on the suction side , also the fuel would keep it toasty in there and no problems.



My question to the crowd is what does dodge use on their gassers for a pump , hopefully a pump in tank??? and if so how much psi and how much flow??? To me the pump in tank is the ultimate as long as you dont run then dry!!!!!!!!!!!!!!!!!!!!! Kevin