rnb_cattle

I had to go to the dealer for a engine light, (MAP SENSOR LOW VOLTAGE) turned out to be bad connection to the map sensor. Anyway, I was talking with the mechanic (who seemed to be pretty knowlegable) and was talking about Fuel Pressue. He told me that Dodge does not care anymore about the old spec. of 7psi supply pressue. He said they switched over to a flow rate which they measure by taking a line off and measuring the time it takes to fill a certain amount. Basically he said all they claim the pump needs is to make sure the filter canister is full and the FP will be ok.

Has anyone else been told this.. and also, I would think that if you are measuing PSI at the FP intake, then there would be correlation to flow??

CNeubauer

That seems to be the story Dodge is going with these days and I think it has to do with them going to the in tank fuel pump but with the same sized fuel lines flow and pressure are directly related and unless there is zero back pressure in the fuel line (which there isn't) it would be impossible to maintain the correct flow rate while dropping the psi. My personal opinion is Dodge is getting tires of warranty claims on the VP-44 and they know the in tank fuel pumps aren't up to the task but they figure that by the time that problem catches up to the truck owner's the trucks will be out of warranty so it won't be their problem.

hotdram

Flow rate (volume/time) is the measurement they now use to determine if an LP is bad or not. Just had my VP replaced under warranty and they told me that when the stock LP got hot, the volume was below minimum spec (forgot what spec was). They wanted to replace the stock LP with an intank pump for $800. I said no. I replaced the stock LP with a Cummins campaign pump for a temporary fix and now have a 95 GPH FASS HPFP sitting on my work bench waiting to be installed.
FWIW, my fuel pressure was always good, the VP-44 just went bad. I had dead pedal and hard starts. I was running Smarty s/w 5 when dead pedal happened the first time. I put it back to stock and ran if for about 500 miles with no dead pedal issues, but the occassional extended crank times (hard start). If the dealer hadn't replaced it under warranty, I would probably still be driving with the VP-44 that went bad until it totally crapped out.

~Rob

Thomas

Probably most dealers have been told: TSB 14-002-03

Bratkid63

I purchased an interactive CD rom from Bosch that describes in detail, and has a lot of good graphics, the operation of the VP44 pump. I am going to present some information here directly from the CD, along with some personal interpretations and I welcome input / criticism.

I quote from the CD: "The fuel must be supplied from the tank to the interior of the pump. In all three pump types, this task is accomplished by a vane type supply pump" (Note: The CD also covers the VP37 and VP29/30.) The vane pump they are referring to is the one internal to the VP44, not any external pumps.

What does this mean? Apparently in most applications, the internal vane pump within the VP44 is sufficient to draw the fuel from the tank, and is actually the case on some automobiles it is used on, such as the Audi A6 TDi. I would suggest the reason for the additional lift pump on the CTD is the fact the fuel tank sits rather low and far away from the VP44 as installed in the Ram. Vane pumps do not draw well without at least minimal head pressure, and would be difficult at best to pick up a prime if the fuel system were to leak back into the tank after sitting, engine off, for an extended period of time.

So what about adding additional lift pump pressure at the inlet to the pump? The inlet to the pump feeds directly into the VP44 vane pump inlet cavity. The size of this cavity increases in size as the pump rotor rotates. (This is what draws the fuel into the VP44 on vehicles without a lift pump.) It would seem as though the vane pump will only allow a defined amount of fuel into its cavity, and increasing the lift pump pressure from say 5 psi to 20 psi would have no effect on this volume as fluid is essentially non-compressible. (Even if the fuel pressure existed at 20 psi within the vane pump chamber, this would not correspond to any additional fuel being "pushed into" the vane pump.)

So what happens to the excess pressure delivered by an upgraded lift pump? Based on my reading on this forum and others, I believed this excess fuel somehow was used for additional cooling and lubrication of the VP44. The fact is, this extra pressure does nothing but reside within the fuel lines and filter(s) between the lift pump and the VP44 and/or is internally regulated within the lift pump. The fact is, the VP44 will only draw in as much fuel as the internal vane pump allows, and additional pressure will not change this, unless it is high enough to exceed the design limitations of the vane pump.

What of this pressure control valve, you may ask? Again I quote from the CD: "Since the delivery quantity increases as the engine speed increases, and the delivery pressure thus also rises, pressure limitation must be provided for within the pump. This task is taken over by a pressure control valve. If the pressure in the pump becomes excessive, the force of the valve spring is overcome and the fuel can flow back into the intake from the pump interior for purposes of pressure compensation."

The inlet of this valve within the fuel circuit is at the outlet of the internal vane pump, and the outlet of the valve is at the vane pump inlet. What this means is in VP44 applications that use no lift pump or a lift pump with an output pressure below the rating of the pressure control valve, excess fuel pressure is short circuited right back to the VP44 inlet. However, if a lift pump has a higher pressure rating than the pressure control valve, fuel pressure entering the high pressure pump of the VP44 will be higher. What does this accomplish? Nothing that I can see, except possibly increasing the possibility of leakage.

Now, why does a failed lift pump destroy a VP44 when there are vehicles operating without a lift pump at all? When a positive displacement pump (vane or gerotor) stops operating, it also stops or seriously impedes the flow of fuel the VP44 is desperately trying to draw. I would suggest that a lift pump that quits and completely blocks fuel flow is better than one that allows a minimal amount of fuel to bypass it's internal parts. The one that blocks flow completely will kill the engine immediately and possibly save the VP44 from destruction, whereas one that allows minimal flow will cause the VP44 to cavitate as the engine struggles to run.

One thing the CD didn't touch on was any cooling effect the fuel has on the electronics atop the VP44. Based on what the CD did cover, it becomes obvious extra fuel pressure will not generate any additional flow through the VP44.

In summary, it would seem any positive pressure that exists (at all RPM's) at the inlet to the VP44 would be sufficient for it to operate as designed. I have somewhat proved this as my truck has had the so-called upgraded in-tank pump installed by the dealer. The fuel pressure gauge indicates 8 psi at idle, 6 psi at cruise and about 3 psi wide open. This pressure only deviates from these readings when the fuel filter starts to clog. I have operated this truck for many miles with these pressures without any problems. (Truck is bone stock performance wise, and will probably stay that way.)

I need a real expert to tell me what I'm missing, and why I need to upgrade my fuel system.

blackdiesel

I think the intank is just fine, for a stock truck. If you have a in tank and a chip, bigger sticks or both, I think a helper pump is needed. JMO

Carp

I agree with Blackdiesel and I have the same CD. It was very informative. I have the in-tank pump, and with my chip and bigger sticks the fuel pressure could be drawn down to almost zero, leaving no room for a restricted fuel filter. The VP 44 needs a positive pressure on the supply side. I installed an additional pump but also a regulator to prevent "deadheading" the pump.I am going to run it @ the current pressure setting unless I get a premature failure of the Carter (they have a rep). If that happens, I will lower the pressure and see what happens. I think Bent Valves mentioned the quality of solder being used as a possible culprit for the electronic failures atop the pump. I would like to know the reason Bosch and chrysler figure 8 psi is the acceptable pressure to run the stock truck. I am sure it is a good one. Too bad more money wasn't spent on the intank module regulator. It is the weak point.

J BODY

I still have the original lift pump on my 01. 12-13 @ Idle, can pull it down to 4-5 at wot....doesn't bother me a bit. EZ, RV275's here so no "wild" mods on my 01.

One thing I did do back in the day was to do a 20 sec volume check of my on engine pump VS an intank pump I installed on a customer ride. The intank pump put out quite a bit more volume.

VP equipped or common rail.... I have YET to have an issue with a "bad" in tank pump.

camelracer

I excess fuel is recirculated within the VP44 pump why are out trucks equiped with a fuel return line?

bentwings

I don't want to seem critical because this is a good read. But I do have some questions.

So what is being said is that whatever pressure the lift pump provides as long as it is positive and enough volume capability to supply the VP-44 at full throttle even with mods is good. Just for example say 3 psi at the very minimum. Also noted is that the fuel simply remains in the VP-44 untill used and only what is used is replaced by the lift pump. So the lift pump just churns away and provides some volume at a pressure.

According to this at 20 mpg and 60 mph there is only 3 gallons of fuel passing thru the VP in one hour. And an awful lot less when coasting.

So the questions are, why is there a return line then if no fuel is supposed to exit the VP except from the injector ports??

Why are we told that there must be lots of flow to cool the VP??

Why does the tank heat up to 125+ deg sometimes if no fuel is being returned to from the VP?? Not buying because it is hot outside, nor reflected heat from the road, nor heat from the muffler....haven't got one. Why does my tank get warm enough to melt the snow off it in the winter time??? Something is putting heat into it.

Sask

These subjects have been covered so many times in this forum and others... and still there's a lot of confusion.

(1) The rotary vane design of the VP-44 is subject to more stress than the piston designs of IP's that preceded it. Two particular stress points are the vane itself - which has a tendency to deform, and the pressure compensation valve, which can fail.

(2) Very early VP-44's did not have proper quality control in the manufacturing process. Burrs, warped shafts, and bad-sealing valves plagued these units and often caused mechanical failures. These problems were largely resolved by using better manufacturing techniques, better quality controls, and better materials after 2000 model year.

(3) All original VP-44's (through 2002) were equipped with electronic control packages that often malfunctioned after repeated thermal cycling. The breakdowns were related to the quality of materials, such as solder, and the quality of the components themselves. These problems were largely resolved by the Fedex redesign - Bosch retrofitted thousands of Fedex delivery trucks with new pumps equipped with better-quality packages.

(4) Any Bosch-approved remanufacturer is required to use upgraded mechanical and electronic parts redesigned and manufactured after 2002. Properly rebuilt VP-44's have a much better record than OEM - Bosch claims that the fail rate in 50,000 miles has been cut by 90%.

(5) Fuel flow does not cool the electronics package enough to make any appreciable difference. The problem is thermal cycling breaking down the components of units that are not built to withstand more than a few thousand cycles. Most of the damage caused by thermal cycling occurs as the engine warms up, and after it is shut off. In both cases, fuel flow makes no difference. Either you replace the package with a more durable one, or you somehow keep the package at the same temperature all the time....

(6) Fuel is used to lubricate and cool the mechanical components of the VP-44, and is recycled through fuel return lines. That's why the temperature of the fuel in the tank rises, and why it is not a good idea to run below a quarter of a tank on a hot summer day. Lubrication is more important to pump longevity than cooling. On the other hand, hot diesel fuel does not lubricate mechanical parts as well as warm diesel fuel.

(7) Low fuel flow will contribute to the chances of an internal mechanical failure, but the VP-44 can draw enough fuel from the tank to forestall failure for tens of thousands of miles. Rather, the problem has to do with how the lift pumps fail. If they fail and fuel flow is partially blocked, the IP will fail faster. Or, if the check ball valve in the lift pump fails (the ball will fall out of its seat and literally bounce back in and out as the pump operates), then fuel pressure to the IP will be erratic - causing pressure surges which can deflect the VP-44's vane, wear the shaft bearings, and spring the valves fairly quickly.

I understand the logic behind DC's in-tank lift pump fix, although I don't think it's good logic. If it fails, the in-tank pump will not impede the VP-44 from sucking fuel directly from the tank. If it fails, the in-tank pump does not have the same check-ball valve design which will cycle pressure surges erratically. But the real solution - which DC did - was to abandon the VP-44, which was a bad design for the application.

HOHN

The VP-44 was never actually intended for the CTD application.

In fact, when it became apparent that the P7100 could not meet the future emissions requirements (mostly due to lack of computer control), the main engineering thrust was applied to the High pressure common rail design. The HPCR was the goal all along.

However, the HPCR was simply not ready in time to meet the emissions regulations that took effect 1 Jan 1998. Hence Bosch used on off-the-shelf solution in the already designed VP44. The goal was to use the VP until enough time could pass to make the HPCR a mature design that was production-ready.

All of what has been previously posted is accurate and true, imo. No need for tons of FP at the VP-- you can't force the Vp to take more than it wants. Give it clean fuel at positive pressure under all conditions and it's happy, imo.

The main consideration imo is to ensure that any LP will "stay out of the way" if it fails. Many guys have setup their LP rigs with a bypass check valve on them that would allow the VP to suck right from the tank if the pump fails. This is a good feature, imo.

bent valves

Here is a link to a Bosch web site that shows the VP-44 was designed for passenger cars, light commercial vehicles, buses, small off-highway engines (stationary engines, construction and agricultural machinery)

http://rb-k.bosch.de/en/fieldsofappl...utorpumps.html

Reading down to the power ratings it says the design supports between 45 KW to 25 KW per cylinder. In our Dodge trucks that works out to be between 360 HP and 201 HP.
At 360 HP it is injecting 175 mm^3/stroke or 0.000046 gallons/stroke. At maximum engine RPM, 3200, the VP is injecting once for every 2 engine revs or 0.0736 gallons. Converting this to gallons/hour I get 4.42 and this is the quantity of fuel burned per hour at full power if you max out the VP.

My SO VP is rated to inject only 92 mm^3/ stroke when it is making 235 HP. It’s no wonder when you tap the pump wire and add big sticks to make 500 HP like I have done, it is just a matter of time before something pops.