Engine/Transmission (1998.5 - 2002) I suspect a lot of money has been wasted on Lift Pumps

[Lube Man]

After extensively researching as many threads as possible concerning lift pumps I suspect that many have been needlessly replaced.



The LP is an electric motor driven pump. This means that it's output is not directly affected by engine speed. It is affected only by the flow on the output side. Flow on the output side is affected by the amount of suction created by the injection pump as it adjusts to load and throttle settings.



At idle the injection pump places minimum demand on the LP. To limit the amount of pressure that the LP can develop I am lead to believe there is a pressure relief valve that is set at 14 PSI. As the throttle is applied the injection pump requires more fuel. I am also lead to believe that the injection pump pulls suction on its inlet to the extent that the LP pump is almost not needed. This causes the pressure drop on the outlet side of the LP pump.



The question that should be asked of Cummins or Bosch is what pressure if any is required on the inlet side of the injection pump. If the pump truly can operate without an LP then I would expect the answer to be a negative PSI (or vacuum). At some point it is possible that the LP actually might inhibit the flow required by the demand on the injection pump. This condition probably never occurs on a stock engine but most likely occurs when you bomb the engine requiring greater fuel flows than stock.



The LP actually is working hardest at idle because that is when the injection pump would be creating minimum suction at its inlet, thus creating maximum pressure on the outlet side of the LP pump. That is why the Dodge Service Manual only calls for checking the LP pump at engine idle. That is when it is actually working the hardest. While a good new pump should be putting out 14 PSI I assume that there is eventual wear in the pump so Dodge has set 10 psi as the minimum allowable pressure at idle.



Sometimes a little extra knowledge is not good unless the knowledge is understood. Most owners do not have FP gauges and drive around ignorant of fuel pressure. Then they go out and install one and right away go into a panic over readings that they do not fully understand. Instinct would indicate that pressure should increase with engine speed just like oil pressure. But that is not the case here.

 

[John - K5AWO]

A good job on the description. To answer your question on the suction pressure on a VP44, Bosch states that it can pull 2" of vacuum and be quite happy.



I don't believe that you will find anyone willing to run their VP44 without a lift pump though IF they were knowledgeable of that fact. I won't. I would also prefer to move the lift pump to the tank to get it away from the engine vibration and make a pusher out of it.

 

[Steve St.Laurent]

Dodge for several years had a spec of a minimum of 8 psi at WOT under load directly from the STAR hotline. Your service manual reads different than mine for my 98:

With the engine running, the pump has 2 modes of operation: Mode 1: 100 percent duty-cycle with a minimum pressure of 10 psi except when the engine is cranking. Mode 2: 25 percent duty-cycle with minimum pressure of 7 psi with the engine cranking.

I've talked directly with Bosch, Dodge, and Cummins engineers a few years ago when I was having lift pump problems and at that time they ALL said that you never wanted to see less than 8 psi and the more the better to a point. All of them said 20 psi (what I was going to be running and still am) was no problem with the exception of having a possible hard start problem. Since that time a Bosch engineer at the TDR nationals said you didn't want to see more than 12 psi - but didn't have any explanation on why the factory pump puts out 15 psi and has a bypass at 14 psi. Dodge now tests the lift pump by volume - not pressure.

 

[EBoyts]

I understand that a fuel delivery system operating under vacuum may induce entrained air into the fuel, and that this is why its better to 'push' the fuel to the injector pump rather than 'pull' it. Anybody know about this?

 

[Gary - K7GLD]

Biggest issue *I* have seen during some flow testing I did with a stock LP, was it's tendency to cavitate when flow was severely restricted, such as when the engine is idling - once fuel demand is increased and decent flow is restored, things are fine - but that cavitation at low demand can create some severe PSI fluctuations - and in some cases, once flow is lost due to cavitation, it will only be restored by shutting down the engine and restarting - at least that was what I saw on mine... Sure is interesting to see actual fuel flow in these systems when using clear hose - a little scary even...



A pusher pump seems to greatly overcome this issue, since it functions at lower PSI, and actually FORCES fuel flow to/thru the stock LP, eliminating the cavitation problem...

 

[mediccummin]

Lube Man why dont you test your theory out for us and run your truck with no LP, then get back with us in a few weeks while your truck is in the shop getting a new VP 44 installed. Or just keep running your pump at zero and see what happens. :-laf

 

[Lube Man]

I just spoke with Steve in Cummins Customer Service Department. He confirmed everything I outlined above. He said that the injection pump does draw input and under certain load conditions it is possible to experience vacuum between the LP and injection pump. As long as the LP pump shows adequate pressure at idle there is nothing to worry about. Again, the Dodge Service Manual refers to 10 PSI as the minimum criteria. THIS IS IDLE PRESSURE NOT WOT!! I am done with this thread. Any further comments I suggest you first call Cummins at 800-343-7357

 

[Greg Boardman-RIP]

I just spoke with Steve in Cummins Customer Service Department. He confirmed everything I outlined above. I am done with this thread. Any further comments I suggest you first call Cummins at 800-343-7357

Why would you even start a thread like this if you don't want to discuss it Lube Man? This has been hashed out for years and now you found out the holy grail? Come on man.



Greg Boardman

 

[Gary - K7GLD]

"Don't confuse me with well-proven FACTS, my mind is made up, and supported by that smart fella at the local Cummins shop who drives a Ford... "



Hey, like the fella said above, REMOVE that troublesome POS LP, and let the VP-44 operate all by itself as Bosch and Cummins planned it from the start...



THEN get back to us in a few months and let us know how it's working out for ya!



C'mon, I *DARE YA*!

 

[mhenon]

Don't go yet...Lubeman

I think we all know there are applications where the VP44 pump doesn't have a lift pump. I would guess they're marine engines, or something, where the fuel tank is above the engine and gravity feed is just fine. So... it doesn't take a lot of inlet pressure to run right.

Enter. . the Dodge Ram... . with the fuel tank below the engine... a screened primary filter within the tank (you can't even inspect this screen)... . a lift pump in the wrong place (should be by the tank)... questionable electrical connection to the lift pump (Gary has brought this up a few times)... and who knows what other gremlins are plagueing the system.

Lubemen has a point... . when things go bad... we change out the lift pump.

I just had a bad pump sent to me and have checked it out... somewhat. The symptoms were: low pressure at idle. . dropping off to 0 pressure at WOT.

I disassembled it and found nothing wrong. After getting it back together and running a few clippy wires to the power leads... it pumps fuel just fine. Is the pump really bad... . hell if I know... . but I'll keep it for a spare anyway.

There's more to this fuel system than the lift pump. I've got a feeling this Carter pump works OK. It gets a bad rap and "is" the cheapest and easiest thing to replace. If you have a one time pressure problem and the lift pump fixes it... it's probably the lift pump. But, those guy's who go through lift pumps like ***** through a goose (love that line)... you've got something else wrong and need to look somewhere else.



JMHO... ... ... ... ... ... ... Mike

 

[rblomquist]

There's probably some truth to everyone's point of view on this one but we all know for a fact that there are thousands of folks driving these trucks on the road right now that have no clue their LP has quit working and you probably couldn't convince them otherwise.



My old neighbor had a 99 like mine and for over 2 years I heard him cranking the heck out of his truck after a fuel filter changout. I finally basically forced him into plugging in my test gauge one day to prove to him his LP was dead. He couldn't believe it; to him the truck was running great (no different than ever). He even made me go over and hook up the test set on my truck in front of him to prove that something was indeed wrong. He put at least 20k on that truck during the time I first met him and when he got his LP warrantied out and God only knows how many thousands of miles it was dead before I moved next door. BTW, that was almost 2 years ago now and his VP44 is still trucking along with over 100k on it.



I would not intentionally run mine with a dead LP but to take the position that any amount of time with even a weak LP will ruin a VP44 is (to a degree) a bit disengenuous/untrue. We get so engrossed with every minute detail provided on the TDR that sometimes we need to step back and look at it from a larger perspective. Again, I won't run mine w/a dead LP but I also won't overreact as long as there's positive pressure feeding the VP44.

 

[DKothe]

Overpressure for cooling??

I was under the impression that the added fuel pressure was for cooling purposes on the VP44, the relief valve let the fuel cool the pump off and sent the heated fuel back to the tank.

Is this anywhere near a correct assumption??

 

[radar doctor]

Just Thanks For This Data

Thanks to all who wrote on this problem. What about on the 03 ???? Are they having any Problem's?? Doc

 

[Gary - K7GLD]

I was under the impression that the added fuel pressure was for cooling purposes on the VP44, the relief valve let the fuel cool the pump off and sent the heated fuel back to the tank.

Is this anywhere near a correct assumption??

YUP - close enough for government work...



As to folks driving for extended miles and periods of time with bad pumps - sure, probably happens fairly often - found a few at local meetings where I took my mechanical guage to do spot checks. Is it advised, or a good idea? NOT by a long shot!



Might be you would get 100,000 miles that way - but MIGHT have made a million if the LP was functioning properly, too. Pumps get changed when other faults are the real problem? Sure, don't doubt it a bit.



But *I*, for one, won't play Russian Roulette, or try to dodge freeway traffic just because I *might* survive - I fully KNOW what the weaknesses are in the VP-44, and since I can't easily remove or alter those weaknesses, it only makes sense to do my best to avoid well proven situations that place even greater stresses on a weak system - regardless of what some new Cummins or Bosch "expert" claims - they have THEIR duds just like any other company, and NONE of them will be around to pay my bill if my VP-44 goes TU...

 

[mediccummin]

Man the guy talks alot of crap then backs out of the discussion when he realizes how wrong he is, I guess we wont see him posting anymore threads. He must be related to the guy that said injectors are a waist of money and dont add more power. :{ :-laf

 

[Lunkerman]

WOW! I must be one of the thousands! Saturday I decided to change my fuel filter as per Bob Patton's instructions in the latest issue of TDR. Up to this point, I have only been swapping out the filter and not draining the whole canister. So i cleaned it out, put the new filter in and closed it up. Did the bump start thingy and then tried to start it. CRANK CRANK CRANK, NO START.

Unscrewed the cap, DRY AS A BONE! So I poured some kerosene in it and cranked for a while til it started. Soooooooooooo, How long have I been driving around with a dead LP? 72k on the odo and never had a problem other than when my crank sensor died. Mileage has improved to 22mpg. Heading for the dealer tomorrow for a new LP under warranty. I'll request he check my vp44 also.



John

 

[RussW1911]

I just want ot know what lunkerman is doing to get 22 mpg :--)



And, I was told by a well known vendor (to TDR atleast) that anything under 10psi on the fuel pressure is wasted horsepower. I idle at 14-15 but can really drag down the psi if I have my COMP on. Don't have it on very often. Need a clutch.



Russ

 

[rweis]

On the DTT site they talk about Bosch wants 12 - 14 psi into the VP during engine running.



My thinking is to regulate the pressure to the VP to be as consistant as possible and in the 12 - 14 psi range. Hence my theory of the bypass regulator after the lp and set at 12 psi.



I want the VP to see a very stable smooth even flow (psi) of input pressure regardles of idle or WOT.



I only have 37k on the test, and time will tell. even if I replace a lp every 4 or 5 years ( 100k miles ) just because I think it is about time that is cheap.



I just pulled my 13k 5er through the Smokies for a week and had WOT for up to 30 minutes up 7% grades steady (1250*) and the lp and VP pressures held just fine. I am satisfied with the setup until proven otherwise.



Bob Weis

 

[rblomquist]

Some of these threads are getting a little out of hand lately IMO. The greatest thing I've enjoyed about the TDR is the interaction, brainstorming, and ingenutiy of the members.



We shouldn't be flaming someone who brings another outlook to the table, especially if they have done some research. Doesn't mean that it's to be taken as gospel but we should be able to bang around theories & experiences without slamming each other. Maybe I'm just reading into a tone in some of the posts that isn't there but it sure seems like I read more and more threads with name calling posts in them than ever before... ... ... ... ... .

 

[Gary - K7GLD]

Gotta be VERY careful with posting theories, especially on sensitive and somewhat controversial issues. Many newbies here, and casual readers as well, might tend to take opinions as gospel, and act accordingly. Much of the basic knowledge floating around here is based on time proven fact - much of THAT derived from failures by those who thru ignorance or stubborness, chose to "do it their way"... Until they learned better...



To accept a course of action solely because a single Cummins or Bosch employee suggests it might be sorta foolhardy - I personally have heard 3 DIFFERENT operating theories direct from Bosch "experts", and one from a guy who works on them daily at an authorized Bosch center - I'll take the opinion of the guy who actually WORKS on them daily over that of an engineer in a glass cubicle any day - but HE can be wrong too!



One tree doesn't make a forest - and one opinion doesn't rate acceptance as an iron-clad FACT, either!



And to allow radical opinions that go against all known and established facts to go unchallenged is foolish, and unfair to those new truck owners who as yet haven't been fully exposed to a larger baseline of knowledge gained from past experience.