Long-Term RASP Pump Use and Pressure Decline

[MacGreenie]

1998 Dodge Ram 2500 4WD extended cab w/ bone-stock motor. 200K on original motor and transmission.
Been running a RASP system since 2004.


Got tired of boost pump (failing) issues and installed a Westach gauge displaying dual fuel pressures for pre-and post filter. So now I could keep track of the health of my overworked Carter lift pump (an obvious and well-documented weak link).


I did install a larger fuel flow line from the filter housing to the VP 44. I guess that helped on the supply side of things… I never really had any problems with the engine bucking due to lack of fuel but in any case I put one of those on. So there’s that.


In order to get around the ticking time bomb of a failed lift pump killing my VP 44, I installed the RASP system from DTT in 2004. Yes, I was an early adopter and it has been a great system but apparently after over 100,000 miles that Li’l pump seems to have developed an inefficiency at low rpm. I can only achieve five PSI at idle ; and it takes about 1100 to 1200 RPM to get to a solid 12 psi which matches what a healthy Carter lift pump will do at idle. When the system was new, I could get 12 to 13 at idle on the FASS pump alone. I have used three separate mechanical test gauges to make sure that I’m getting a proper reading of this low pressure condition. All three of those gauges have been consistent… This was to make sure I wasn’t chasing any bad data I might get from my Westach pressure sensors because they have a history of reading about a pound and a half to 2 pounds high.


I have done all sorts of troubleshooting to include disassembling the check valve and the fuel pressure regulator that dumps back to the tank… I think that spills fuel back to the tank at about 12 psi… And it’s none of those things. It truly appears that the FASS Pump gears have worn and it now bypasses internally at 900 RPM at idle. The system has been on for over 100,000 miles so I assume somewhere that internal wear (would/could/might) be inevitable?


My interim solution was to change the pressure setting on the Hobbs switch so that at idle RPM the electric lift pump will cycle and maintain 10 psi. Once you get the RPM to 1250, the RASP pump takes over and satisfies the pressure requirements for 11psi and above for driving conditions from 25 miles and upwards. For reference, I get 16 psi at wide-open throttle with the RASP providing all of that.


Not sure how many of you are still using the RASP system or similar designs like the MITUSA or Fuel Boss. Both of these systems seem almost identical to what DTT was putting out with the original RASP. All the plumbing works quite well and everything has been extraordinarily reliable… Except for this low RPM inefficiency that I seem to be experiencing twenty years later. Of course, five psi at idle is perilously close to the point that you’re risking your VP 44‘s future health. I have examined and tested the fuel pressure regulator to make sure that it is not opening prematurely (or is jammed open by debris) and dumping fuel back to the tank and thereby mimicking a low pressure condition.


I’m interested in anybody else’s opinions regarding using the Hobbs switch to fool the system into providing sufficient pressures until the RASP can take over at higher RPMs.


Because the RASP is already pulling fuel from the tank on the same line that the Carter pump uses to pull from, I like to think that the RASP pump is making it easier for the Carter pump to provide filter-can pressure ; so, because of this lift/assist effect, the Carter pump mounted on the engine in the stock position may last longer than normal, methinks.


At the end of the day, I could order a new pump from Glacier Diesel and likely solve the problem. Their pump on their Fuel Boss system seems to be identical to the RASP.


I’m just wondering if I can limp along playing sleight-of-hand with the Hobbs switch. I have nothing to lose and I have always carried a spare Carter lift pump in case everything goes south on me.


Even more, I wonder if anyone else is experiencing long-term wear on the same type of positive displacement pump… I’ve been running one for 20 years so that’s a pretty good data point for determining failure/degradation of service.


Your thoughts?


MacGreenie

 

[petersonj]

Of course, five psi at idle is perilously close to the point that you’re risking your VP 44‘s future health.

This is not true. The lift pump on VP44 fuel injection system has the same exact duties as the mechanical lift pumps have had for many decades before the VP44 system was developed. That duty is simple, to provide a positive fuel pressure at the VP44 inlet to ensure there is a plentiful supply of fuel. That is the only duty of the lift pump. Nothing else. So, if there is a positive pressure at the VP44 inlet, the VP44 is getting adequate cooling flow under all operating conditions.

It is the internal positive displacement vane pump (driven by the engine at camshaft speed) that provides all the flow needed for all internal VP44 functions and for the return fuel flow to fuel tank via the 14 psi overflow valve. Any fuel flow that is not utilized is returned back the inlet of the internal vane pump via the pressure regulating valve inside the VP44.

When VP44 engines first came out, many failures of the lift pumps occurred. Many failures of the VP44 also occurred. An immediate association was made between the two components and very quickly VP44 failures were blamed on faulty lift pumps (the beginning of a myth). To make matters worse during that time, it was assumed that the 14 psi overflow valve inside the VP44 was directly connected to the lift pump. So, another myth evolved from many sources stating that if one didn't have more the 14 psi lift pump pressure, then there was no cooling fuel passing through the overflow valve in the VP44 and returning to the fuel tank. Simply, not true.

What was not told was that Bosch recognized that several serious problems existed inside the VP44 that needed to be addressed. Some of those problems were seized rotors (lack of quality deburring process), ruptured diaphragm for dampening pulsations (inferior materials), timing piston and bore sticking / seizure (inferior materials), PSG soldering quality, etc., just to name a few. To Bosch's credit, these problems were fixed and these remanufactured pumps replaced the faulty OEM VP44's, but the public was not made aware of the improvements. As a result, the myths continued to grow gaining support through many forums.

Some members of forums have gone out of their way and with some expense have tested the VP44 return flow circuit using a flowmeter. I, too, performed flow tests using a different method that clearly shows there is no relationship between lift pump pressure and fuel returning to tank via the 14 psi overflow valve. The diagram below shows how I set up for the test:

Both tests were done at engine idle.

During the first test the lift pump was operating - return flow measured 19 gph.

During the second test the power to the lift pump was disconnected. Return flow measured 19 gph. Nothing changed. The VP44 internal vane pump drew fuel from the tank through the one-way check valve, thus bypassing the non-operational lift pump.

I even took it one step further and drove the truck to town and back (28 mile roundtrip) in the second test mode. I shut the engine off several times and restarted it during the trip. I performed several wide open throttle applications. No stumble, no lack of power, just smooth operation like always. This is with RV275 hp injectors and a Smarty mild tune.

So, I mention all of this because, although you may want to make your current system operationally reliable, there is another option which I believe to very reliable and simpler to install and maintain. That would be using an electric frame mounted lift pump of your choice with the lift pump bypass circuit installed, and a low fuel pressure warning light system installed. Of course, if you should entertain this idea, you would have to dismiss the above-mentioned myths. That could be hard.

Just so you know that I practice what I am posting, here is a brief history of my truck regarding the fuel system:

November 2001 - truck new

July of 2004 at 67,000 miles - 0214 code (timing piston failure) in Continued to drive truck for one year.

August 2005 at 87,725 miles - (yes, 20,000 miles later) - VP44 and Lift pump Replacement by Dealer - Warranty covered VP44 and in-tank lift pump conversion (VP44 failed, OEM lift pump did not fail).

OEM lift pump: 12 psi @ idle, 7 psi @ 2500 rpm WOT.

New in-tank lift pump: 6 psi @ idle, 3 psi 2500 rpm WOT.

If I would have believed in the above-mentioned myths, I would have run screaming back to the dealer. I did not because 3 psi is a positive pressure and the internal vane pump takes over from there.

April 2016 at 251,000 miles - installed used FASS frame mounted lift pump (somewhere between 60-90 gph). In-tank lift pump has now logged 163,000 trouble free miles and is working fine. I made this modification just in case the in-tank lift pump failed. It would much easier to replace a frame mounted lift pump should a failure occur while on the road. FASS lift pump 12 psi at idle, 6 psi at 2000 rpm

Today at 364,000 miles - frame mounted used FASS pump has logged 113,000 trouble free miles. Remanufactured VP44 has logged 276,000 trouble free miles.

I apologize if I provided too much information, but I have been trying to break the myths surrounding the VP44 fuel system. I can't achieve that unless I can back it up. And, of course, everything I wrote here is just my opinion.

Something I forgot to add. I left my lift pump bypass fuel circuit in place in the event I have a lift pump failure. If that happens, the VP44 internal vane pump will continue to draw fuel from the tank and no harm will come to the VP44 injection pump. My low fuel pressure indicator lamp will light, but I will be able to continue driving. As hindsight, I should have installed this feature 20 years ago!

With what I have learned over the years and with a lift pump bypass circuit in place, and with the improvements Bosch has performed on the VP44, I now believe the VP44 fuel injection system is very reliable and will provide a long service life.

- John

 

[Turbo Terry]

I had a rasp from the early days 2003? It work very well for the most part. I had some leaking on the shaft but put little shaft collars on to keep the dirt out and replaced the rasp pump. No more leaking. I wore out a couple cog wheels dirty roads etc and few belts. Ran them very loose. 17-18 lbs pressure idle and up constant. Glacier fuels still sell them and told me rather recent they still sell quite a few. Little expensive but never changed another lift pump after install .Before rasp changed out 11 lift pumps at $175 a piece Could do it in about 40 minutes I got so good at it. Sold 99 last year buyer didn’t know arasp from a hole in the ground. Good luck to him

 

[MacGreenie]

Thank you both for your well-researched response(s); and I especially appreciate the effort that you put into determining the truths and the myths surrounding the VP44 failure conundrum.


In researching this, I watched a video on another website of a fellow doing a bucket test in various modes of operation to determine how much fuel was bypassed back to the tank by the VP44… And it absolutely falls in line with all your information and experience. Very revealing indeed!


Yes, I will have to let go of the notion that more pressure at the VP44 is better. It appears that my current set up, while not producing the idle head pressure it did when it was new, is still sufficiently capable. 5 psi at idle should be enough to keep the system happy.


It is without a doubt true that any amount of head pressure to the VP44 will keep the pump healthy. The 14 psi bypass at the VP44 pump created an opportunity for a well-circulated yet totally false engineering concept regarding head pressure to take hold in our community.


I am intrigued by the bypass check valve design that would prevent the VP44 from cavitating should an electric boost pump fail.

My RASP system has gauges that show me if the primary pump has failed which would be my signal to then activate the electric pump for continued reliable/safe/non-cavitation operation.


Yet, I like the simplicity of the check valve/bypass design which takes over automatically and provides a clear and unobstructed suction pathway for the VP44 to draw fuel in the event of a lift pump failure.


I guess at this point, I could continue operating my system as installed and readjust my Hobbs switch back to the original 4 psi setting. Apparently, there is no need for me to bump up the cut-out for the stock lift pump to 10 psi (other than to make myself feel good!) because I’m getting a solid 5 psi at idle already.


Such food for thought you have provided…


I hope others read this thread and discover the disconnect between causation and correlation as regards VP44 build quality and the actual/intended role of the lift pump pressure output.


I’ve been on this site for over 20 years, and it is the best money I have ever spent. TDR members are always helpful and exceedingly well-informed. Thank you both for your time.


Safe motoring.


Regards, MacGreenie

 

[Turbo Terry]

So I had a interesting issue with the rasp that needs to be talked about. The brass in-line thing. Cant remember the proper name. The thing that held the spring and washers to adjust the fuel pressure It had nozzle end that seated etc. bypass valve I think you might call it well I use anti gell in the winter but got a bit of #2 that had gelled up a bit in some 5 gallon jugs . My rasp had the warning light that would come on and the start the lift pump would come on about 8-9 psi. Also I had a fuel pressure gauge. This bypass valve was located and connected at the bottom of the fuel filter housing a real bad place to get to especially on a hot engine. On a major road trip north of Whitehorse I lost fuel pressure the light came on. We camped and let it cool off took the bypass valve off opened it up rinsed in some gasoline put it back on and we’re good to go. Seems a bit of waxing got on the seat etc I stopped Yukon Pump in Whitehorse and they helped me by making up a hose to move the bypass up to the top of the motor easy to get to even when hot very nice. I called Glacier fuel and bought a spare bypass to carry in a small jar ready to go. When I got home and changed the fuel filter you could see the gelling on the filter. Little bits been getting off and going to the seat and opening it and making my fuel pressure drop. Normal was 17-18 lbs So the seat can get something stuck in it etc and always carry a spare fuel filter and use antigel properly

 

[Turbo Terry]

Clean your bypass pressure valve maybe that will help you

 

[petersonj]

@MacGreenie , I appreciate your well thought out response. I also appreciate that you did some checking on your own.

Either way you go, I think that you will find a good solution. If you keep your current configuration, I recommend to consider removing your engine mounted electric lift pump and installing it on the frame rail near the fuel tank. Two benefits - 1. Gets the lift pump away from heat and engine vibration. 2. The lift pump will become a pusher pump and its inlet will be charged with fuel with a fuel tank half full or more - much less stress on the lift pump. It will also be easier to install a lift pump bypass circuit should you decide to go that direction.

Also, here are some of my thoughts on a fuel pressure gauge versus a fuel pressure warning light. Both work well and it really becomes down to being a personal decision. I prefer the warning light system mainly because it will likely catch my eye when the light comes on, or even flickers. A fuel pressure gauge will allow for monitoring slow changes over time, but an indicator light will offer a similar observation as well, for instance, the warning light stays on longer than usual after starting the truck, or under hard pulls a flickering of the light occurs. In my setup I use an adjustable fuel pressure switch to dial the warning light operation into a useful operating zone.

Be sure to let us know how you resolve your issue.

- John

 

[GAmes]

I noticed that the myth of 2SO increasing the life of the VP44 wasn't mentioned. Has that bologna finally gone the way of a dial telephone?

 

[petersonj]

@GAmes, I have never challenged the use of 2 stroke oil mixed into the fuel and its effects, primarily because I have nothing to base it on. If I don't have any facts, then no challenge.

My truck receives the far majority of its fuel in the state of Oregon. Oregon mandates a minimum of 5% bio diesel and that mandate has been in effect for years. Some subscribers of the Mopar1973Man site swear by the 2 stroke oil addition and say that if biodiesel fuel is used, then 2 stroke oil is not necessary.

I can tell you that I don't add any 2 stroke oil when I am out of state on long trips. So far, it has not seemed to have affected the life of the VP44 currently on my truck.

- John

 

[GAmes]

Actually, the perveyors of the myth had nothing to base it on. That is why I found it so strange.

 

[Turbo Terry]

2 stroke one ounce per gallon made my 1999 24 v purr like a kitten.

 

[Turbo Terry]

But 2 stroke oil is expensive and getting harder to find all the time. Try a quart in your old 5..9 and see what you think

 

[GAmes]

2 stroke one ounce per gallon made my 1999 24 v purr like a kitten.

I actully sourced a sound meter and measured the sound levels with and without 2SO in the tank (my boat hated me for wasting it's oil). Not one iota of difference in sound levels. I attribute the myth to a placebo affect. You expect the engine to sound different so it does. The synthetic 2SO for my new boat costs way too much to waste it in a diesel tank

 

[BarryG]

I had a rasp on for several hundred thousand miles. When mine did as you described I would need to change the bypass valve internals or clean it. Take the valve apart and you can get to the seat. Some are all brass and precision lapped to fit. Some have a rubber seat. You can get just the parts you need from kinsler.com. Look up jet can, primary or secondary bypass valves on their website. They are very helpful on the phone or at least used to be.
I found that after many thousands of gallons of fuel the piston or seat starts to erode just enough to keep the valve from closing or I have even found debris In there and a cleaning may fix it

 

[Turbo Terry]

Yes and yes

 

[Topzide]

I would think that if you wanted to add some lube to your fuel, why not just add MMO(Marvels Mystery Oil) and not waste your 2SO. I've added MMO to the diesel tractors fuel due to age of tractors, small engines to help prevent the corrosion that occurs due to ethanol based fuel of today. Have had good results in small engines and hard to tell in tractors but will keep using in either case. JM2C and what I've encountered. Like they say, "your truck your choice". Just keep them running!!!!!!!!!!!!!

 

[Turbo Terry]

Yes I have used mm oil also.

 

[MacGreenie]

Thank you all for your inputs. Good info to be sure.

Here are my possibilities:

Bypass valve: Yes. I have disassembled and checked this seven times….including adding a shim to increase peak pressure. In the past, rapping the bypass valve with a screwdriver handle would return the idle pressure to normal. And then disassembly would be required at other times. In my recent experience, if I clamp off the output to the bypass at idle it has no effect. At higher RPMs with clamp on the tank return line, the pressure spikes to upwards of 30 psi. So the bypass valve appears to be operating properly. So I will not purchase a new bypass valve yet.

I guess this points to a weak or internally bypassing RASP. But with 5 psi at idle and a steady 12 to 14 under normal driving conditions, I am satisfying the VP44 need for head pressure. Conceivably I could do nothing and soldier on under present conditions (RASP at 5 psi at idle). Petersenj, thank you for your input/experience/wisdom on actual VP44 pressure needs.

So pursuing added head pressure (the mythical 14 psi at idle) is merely a feel-good measure. And to feel good, I can pay $328.00 for a new pump. A possibility to be sure.
At present, I have the lift pump bumping along at 10 psi courtesy of the Hobbs switch…one way of making myself feel good! Now, interrupting the power repeatedly to the lift pump may cause some wear….but I’m willing to see what happens. I will report back on the thread what happens in this regard.

 

[petersonj]

In my recent experience, if I clamp off the output to the bypass at idle it has no effect. At higher RPMs with clamp on the tank return line, the pressure spikes to upwards of 30 psi

If there no slipping of the belt, this test clearly shows that the pump has lost much of its volumetric efficiency. Internal leakage is so great at idle that the fuel is leaking around the gears inside the pump and so much flow is being lost that relief pressure cannot be reached.

It would be interesting to know the volume output of that pump - as in cubic inches per revolution. With that information, the output volume could be calculated exactly for any given engine rpm. But, alas, it seems that none of the lift pump manufacturers (mechanical or electric) want to provide that information.

If you ever disassemble the pump and you are curious to know, pump volume per revolution can be calculated. There are pump volume calculators on-line that will provide the formula to find the pump's volume output in terms of cubic inches per revolution. They also explain how to measure the gears in preparation for using the formula.

You've done good work so far!

- John