Do we even need a functioning lift pump?

[Pit Bull]

TXRam





Registered: Jan 2000

Location: TX, USA

Posts: 569



Well, I just have one more thing to add right now - per the Bosch material I received, the VP44 was designed to suck fuel from the tank through a filter! No lift pump in the picture. So, I'll revert to my previous statement, as long as you have greater than 0psi at the inlet to the VP44, your pump will be fine IMHO.



Wanted to throw that out since we've been talking a bunch about pressure at the pump, higher pressure lift pumps, etc.



Got this from another thread. TXRam got the CD on the Bosch VP44 and he stated earlier in this thread that Bosch did not even include the requirement for a lift pump in the design of the VP44. Now I know that having a lift pump is a good thing but I wonder if these trucks could run forever without a functioning lift pump. Best that I can figure, is mine ran for close to 8,000 miles with a dead pump and I did not know it until I checked the lift pump psi and it showed "0". I know Bill K did some research on the and TXRam also. Just wondering if we are chasing our tails on this one. Don't get me wrong I want my lift pump to work and now that I have a FP guage I will monitor it and have it replaced if it fails but it might not be as big of a deal as we all thought it was. Flame away

 

[Shooter]

I guess my question is : if the vp44 does not need a lift pump, how much draft will it pull,or is it designed for gravity feed ????

 

[Lug-nut]

I believe you are probably correct. I have this same engine and the 4 cylinder version of it in various excavation equipment, and no lift pumps are used. The difference is that the fuel supply is usually much closer to the engine, and the power output is quite a bit less.



So... ... I have believed for a while that the lift pump may not be ASOSOLUTLY necessary, but I also will not be driving around without one on my truck. If mine fails however, I will not panic and stop immediately at the road side regardless of where I am at the time.



Just my . 02

 

[DennyDay]

No lift pump???????????????

Does anybody think, for even one minute, that if we didn't need a lift pump on our trucks, that Chrysler and Cummins would have included one?





Denny

 

[Lug-nut]

Re: No lift pump???????????????

Originally posted by C. D. Day

Does anybody think, for even one minute, that if we didn't need a lift pump on our trucks, that Chrysler and Cummins would have included one?





Denny

He** I don't know. What I do know is that when my first lift pump failed, I drove it several hundred miles until I could get a replacement, and the fuel pressure was reading zero. I also have read that Cummins as indicated by PitBull does not specify one to be used with this engine.



Why would DC included an unneeded item??? Don't know the answer, but as I indicated earlier, the distance to the tank is substantial, and maybe they are looking for a little assurance of reliability... . Too bad the pumps thenselves aren't reliable huh?

 

[Steve St.Laurent]

The other applications of the ISB also have a lift pump - for example the FL60, FL70, F650, F750. D/C's STAR hotline (the dealer help/tech line) has specified that they want to see a minimum of 8 psi at WOT under load from the lift pump and if a truck comes in and doesn't meet that spec to replace the lift pump. This was reported to us from a member that works at a dealer who got it directly from the STAR hotline. The reason given was that SOME pumps have tighter tolerances than others and on the tightest tolerance pumps less than 8 PSI at WOT can cause injection pump failures. Given all that we know about D/C and warranties I personally am 100% convinced that if they didn't feel it was absolutely necessary to see 8 PSI at WOT under load from the lift pump that they wouldn't spec that and wouldn't be replacing pumps that don't meet that. I also ran on a bad lift pump for a long time (over 20,000 miles) and my pump is still running. But if D/C is spending money to replace lift pumps that don't meet the 8 PSI at WOT spec then I for sure want to see 8 psi at WOT on my truck. JMHO

 

[Doc Tinker]

Regardless of whether they built the VP44 to draw it's own fuel. . after hearing about problems with the VP44 I sure like to have what little protection the weak lift pump will provide, as well as a pusher pump. If the VP44 was about $1250. 00 cheaper maybe I wouldn't worry about it.



Doc

 

[Pit Bull]

I read on that other thread that PSI is not what is important, but flow is what is important. Bill K proved that one lift pump, with "0" PSI at WOT the VP44 was still returning the "same amount of unused fuel" to the fuel tank as it was when a stronger lift pump that had over 5 PSI at WOT. Meaning that the VP44 was getting all of the fuel it required at "0" PSI, and that was on a Uprated engine (bigger HP) then a stock unit. Again I will alway keep an eye on my lift pump and make sure it is working. I think DC has the lift pump on our engines for several reasons. One big one would be it could make a bad VP44 last for at least 100K miles. The nice thing about having a failed lift pump is that if you had one of the marginal VP44 it would more then likely fail under warranty versus waiting to fail on your nickle. Having a bad lift pump could be a blessing in disguise, depending on the mileage on your truck at the time of failure

 

[Chipstien]

What do yall think....

Maybe the cause of the Vp-44 failing when the lift pump goes out is because when the pump isn't working it is like a plug in the line and the VP can't pull through it. Just a thought.

 

[Chipstien]

Originally posted by Doc Tinker

Regardless of whether they built the VP44 to draw it's own fuel. . after hearing about problems with the VP44 I sure like to have what little protection the weak lift pump will provide, as well as a pusher pump. If the VP44 was about $1250. 00 cheaper maybe I wouldn't worry about it.



Doc

I agree. Whether they are neccessary or not I do not want to use mine for R&D.

 

[Mr. C]

JMHO,

Could it be that the lift pump is included for primeing the fuel system after filter service or in case you run out of fuel. The older models had a little plunger pump to prime the system. It would be much faster for inital startup on the assembly line with just a few ignition switch cycles to to prime things,just my thoughts.

Mike

 

[B. Gill]

even if it is not needed, then after filter change how is the VP 44 going to pull fuel from the tank thru the filter for more than 10 feet against the gravity, so IMHO it is needed,please correct me if i am wrong

thanks

bob

 

[Don M]

The VP44 has an internal vane type pump built into the design from Bosch. Part of the design reasoning was born out of the German emission standards, FMVSS/CUR.

Germany has a tougher criteria on design of fuel systems as well.

Things like no fuel can be delivered by gravity feed, no dripping fuel can be allowed to accumulate, and many others.

The VP's vane type pump is not sufficent to meet the minimum standard for fuel delivery to the high pressure side of the VP44 in our trucks in DC's opinion.

Of course some fudge factor is designed into the minimum standard so this would explain the reasons that some guys drive around with less than optimum or non working lift pumps.



If I had a modified engine with the VP injection pump I would use more fuel rather than not enough fuel every time.



The VP also contains an overflow throttle valve to help with cooling the radial piston pump. The overall low pressure stage is so designed that a defined quantity of fuel can flow back to the tank via the pump overflow. This explains the findings of other members in fuel return.

If a guy wanted to learn about the VP44, there is a few tricks he would find out to hop it up, so to speak and get a bit more power.



Don~

 

[MidwestMotorman]

Needing a pump...

I ran about 8k miles on a bad one. It completely quit while I was towing close to 22k loaded. I had put on another few thousand miles before it was replaced. I am sure I have a good VP44 otherwise she would have melted. One can always test their lift pump by unhooking the power wire and driving around. I would want to be under warranty though...