Engine/Transmission (1998.5 - 2002) Cavitation is NOT your VP-44's friend!

[Gary - K7GLD]

Greg, one thing to be aware of and keep in mind about these pumps, is that the motor shaft connects to the pump rotor by way of a nylon connecting gizmo that has also been shown to occasionally fail - either due to defect, or perhaps an obstruction that blocks rotor rotation.



Here's a shot that may permit you to see the motor shaft portion where one end of the nylon/plastic coupler fits:



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That coupler fits up inside the pump rotor, and is only barely visible in the above photo.



So, there MIGHT be a possibility that longer term pump operation at elevated PSI might subject that part of the pump to enough stress to cause premature failure unless some external means is used to re-establish pump operating PSI back down to it's design limit...

 

[rweis]

Let's see if I have this correct:



Insert a sleeve in the Carter OEM lp and it will prevent CIWYM? by preventing the bypass from functioning? You used clear tubing, could you use say copper tubing so there is a better more open ID path?



I have to take a look tonight at the OEM lp spare I carry. This would be too simple, a sleeve of all things. Maybe the motor system is not well made (ie the nylon motor to vane impeller connection), but in a pinch it would work. Maybe the Draw Straw would also help the OEM lp survive by not creating a restriction the pump would have to work against like the OEM canister has the potential to create with clogged screens and restrictive ID fuel pickup hose with significant bends.



My RASP has a 12 - 14 psi bypass valve system on it at the VP44 which should serve the OEM lp to keep the psi down to design limits per Gary's comments.



Bob Weis

 

[Gary - K7GLD]

Bob, a short sleeve of the proper diameter and material will easily slip up inside the intake port on the LP, and effectively block off the bypass port that goes up into the motor section, and totally negate it's function - pretty easy to set it up in a manner to keep it in place and not interfere with normal pumping function...



(EDIT)



I'd bet that taking a short section of 1/2 inch copper tubing, and slitting it lengthwise and spreading it or whatever it takes to make it fit tightly up inside the LP's port would work.

 

[rweis]

Other than different OEM lp motor issues etc, what a simple "fix" to block the bypass. How many years have we been talking about the OEM lp? 4 years at least, all for a 1" piece of 1/2" copper tubing?



I will try to measure and construct a OEM lp bypass blocker in the am out of 1/2" copper tubing (Dremel, here I come, again )



Bob Weis

 

[NoSeeUm]

Nice job Greg!



FWIW measuring amps is the only really accurate way to determine true load on the motor. At 8 psi 60 gph 2. 7 amps seems to be a pretty good sweet spot for the pump. This is the volume over pressure arguement DC is so proud of.



I am still trying to understand your test fully and the numbers you present. Admittedly, I am not sure the amp numbers are exactly what I expected. I am still trying to get my mind around it. Generally more flow is more amps, but the increase in pressure will skew that direct relationship in a positive displacement type pump.



I will say that the 3 psi 1. 8 amp test came out the way I expected. It shows the pump is still working, just not very hard. If the pump were air locked the amps would be almost zero.



This dang pump is so small, hard to think about.



Jim

 

[NoSeeUm]

Other than different OEM lp motor issues etc, what a simple "fix" to block the bypass. How many years have we been talking about the OEM lp? 4 years at least, all for a 1" piece of 1/2" copper tubing?



I will try to measure and construct a OEM lp bypass blocker in the am out of 1/2" copper tubing (Dremel, here I come, again )



Bob Weis

Yeah maybe... .



Notice the highest amps, with the bypass blocked, with the pump barely pumping any fuel.



Positive displacement pumps don't really like to hang out at the point all that well. You would need to ensure that does not happen for an extended period of time or I would think new problems would arise. I would guess that the only reason it rotates at all at this point is because of loose tolerances between the vane tips / sides to the casing. Fuel also cools the motor, if I am not mistaken.



Possibly an external pressure regulator and control the pressure at around 8-12 psi. But to go to the that effort maybe a Walbro or some other such pump would be a better choice as it is a less expensive pump to begin with.



Jim

 

[Gary - K7GLD]

Yeah maybe... .



Notice the highest amps, with the bypass blocked, with the pump barely pumping any fuel.



Positive displacement pumps don't really like to hang out at the point all that well. You would need to ensure that does not happen for an extended period of time or I would think new problems would arise. I would guess that the only reason it rotates at all at this point is because of loose tolerances between the vane tips / sides to the casing. Fuel also cools the motor, if I am not mistaken.



Possibly an external pressure regulator and control the pressure at around 8-12 psi. But to go to the that effort maybe a Walbro or some other such pump would be a better choice as it is a less expensive pump to begin with.



Jim

I suspect Bob is referring to use of the modified Carter along with the bypass regulator he already has on hand - just external to the pump itself, and adjustable if need be...

 

[GHolcomb]

Here are a couple more amp draw numbers for you:



I disassembled the pump and took the rotor out and the motor by itself draws just about 1 amp. It is also very quiet!



I added just the rotor back and got the same 1 amp.



I added the vanes and the current draw went up to 1. 4 amps. The pump is louder with the vanes running inside. I didn't run it but just a couple seconds since it was dry. That tells me that with the relief valve popped and outlet pressure at 3psi the motor is still under a little load. Probably just circulating the fuel through the cannister at that point. For what it's worth the lowest amp draw you would ever see would be the 1. 4 amps.



While I had the pump disassembled I looked down from the inside at the exact location of the sleeve I had inserted into the inlet. To my surprise, the sleeve does not cover as much of the bleed port coming up from the relief valve as I thought. I had imagined it to be almost completely covered, but it really appears to only be about half covered. That means that I am not restricting the flow through the relief valve as much as I thought. It must be enough to keep the pump pumping fuel through and not just recirculating.



By the way, this is a Carter I am playing with. The inside of the inlet looks a little different from the picture Gary posted, but it still gets smaller farther into the pump to keep the sleeve from going in too far.



Another thing is that I am not using banjo fittings, just some customized pvc fittings for my bench testing, so I'm not sure what the exact length of a sleeve should be if you wanted to try it on the truck.



Also, I want to emphasize that this is just one pump on a test stand. I am not claiming anything beyond that! My results may not be typical and your results may be different from mine! I think there might be something to this idea, but I'm don't want to go too far too fast!



Anyone else tested the sleeve idea?



I want to try another test, but would like to check with you guys before I try it.



Here is what I am thinking:



Do a pressure and flow test on the pump as installed on the truck.



I am thinking about taking the schrader valve out of the port at the vp44 and connecting a fuel line there that has a pressure gage and a valve.



Next disconnect the plug on the lp and plug in my test stand plug that I can connect straight to the battery.



This would power the pump without starting the engine and I could measure the flow of my pump with no restriction. Then I would close the valve and measure flow of the pump at different pressures and finally see where the flow stops. This would give me a very good picture of how the lp is performing in it's everyday world.



Is there any reason why I shouldn't try this? Do I need to turn the ignition switch to the on position to power any solenoids in the system or can I do it with no power to the truck?



I just want to make sure I don't damage something here!



Greg

 

[Gary - K7GLD]

As to powering the LP independent of the engine for test purposes, I see no problem - at least that's what I do when I change fuel filters - especially the TP elements in my Frantz fuel filter - I use an extra battery I have available, and disconnect the LP leads from their normal hookup, and power the LP separately to prime the system. That works easily for me, because my pump is mounted down on the frame, and I have a regulator/bypass valve right at the VP-44 that returns excess fuel back to my fuel tank. All I need do is change filters, hook up the LP, and let it run for a few minutes to completely fill filter canisters and lines - works great, the engine always starts right up with no stumbles or related problems...



I'll be interested to hear what you find wrong with the LP from your brother's truck - and whether it's fixable...

 

[rweis]

aside, purging air from fuel sytem



I disconnect the fuel from the VP44 inlet (that has an AN-6 metric fitting) and put an AN-6 cap on the VP44 inlet. As Gary has shown in the past the cavity inside the VP44 is like a rectangular internal cavity with the PSG as its cover. I found if I did not cap the VP44 inlet as soon as I disconnected the VP44 fuel inlet (I mean like I instantely put my finger over the VP44 inlet then screw the cap on (maybe lose 6 drops fo fuel) that about 1/2 - 1 oz of fuel would run out of the VP44 inlet and the start would be a little rough until the chamber filled with fuel and it all settled down.



I then connect a length of hose (15 feet) that I can screw the VP44 fuel supply line onto (the one you just unscrewed form the VP44) and put the other end of that hose back into the fuel tank filler line opening (that has the fuel cap removed).



Bump the starter / lp, and watch the fuel flow back at the hose that is in the tank fill line for air and / or nice full clear fuel stream.



When you get a nice clear fuel stream, go back to the engine end of the tank hose, unscrew the hose (and you will see fuel right there at the end of the fitting ready to screw onto the VP44 inlet again), unscrew the VP44 cap on the VP44 inlet fitting, stick the fuel feed hose onto the VP44 fitting quickly, because it is starting to drip fuel out of the internal VP44 cavity again, and snug up the fitting onto the VP44 input fitting.



I do like the aux battery running the lp though (ECM connector off, battery connector on, because I have to bump my lp once or twice to get clear fuel flow.



Just throwing out what works for me.



Bob Weis

 

[GHolcomb]

aside, purging air from fuel sytem



I disconnect the fuel from the VP44 inlet (that has an AN-6 metric fitting) and put an AN-6 cap on the VP44 inlet.

Boy, I hate to be the new guy but... is the AN-6 fitting the banjo bolt that has the large schrader valve in the stock configuration?



I took the valve out of the inside of that fitting and hooked up my gage and valve, then unplugged my lp and hooked it up to a separate power source.



I got lower flow rates than I expected, but I think that was because of the small hole where the schrader valve sits. However, the amp readings were consistent with what I saw on the bench. The other interesting thing is that at near zero flow all I could get out of the lp on the truck was 14 psi. This was not enough to put it into position to pop the relief valve. I am going to be watching this pump to see if it creeps up in pressure at idle as Gary suspects will happen after a break-in period. If it does I will be in position to test my sleeve on the truck.



I am still using a detachable fuel pressure gage, but would like to start adding some cockpit gages. Looking at Geno's the Westach seems the most economical. I also see there is a choice between sending unit and mechanical w/isolator. Any opinions here?



Thanks!



Greg

 

[rweis]

Opps, I'm sorry, I failed to write that I have removed all the banjo bolts and replaced them with AN-6 fittings in the entire fuel system, filter, VP44 all of them.



I did it a long time ago and forgot to say exactely that. My error.



I guess that only works if you have replace your banjo bolts too.



With that said, Gary's way is better for the largest group of owners.



Again I appologize,



Bob Weis

 

[Gary - K7GLD]

I also see there is a choice between sending unit and mechanical w/isolator. Any opinions here?

I've been using Wastach gauges, and the electronic PSI sender since the truck was new - no problems!



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Sorry for the fuzzy pics - those were taken early in my "photo career"! :-laf

 

[Misenheimer]

pump bypass

I hate to flog a dead horse but I have a question.



The pop off valve located in the lift pump seems to be mounted on the inlet side of the pump and opens by pushing the ball down into the motor cavity. If this is the case then pressure will keep the ball on its seat and not allow it to open.



This bypass seems to be for allowing the VP44 to suck fuel through a dead lift pump. ?????????



I hope that Gary will not mind me using his picture with the flow arrow on the left.



Robert

 

[GHolcomb]

I hate to flog a dead horse but I have a question.



The pop off valve located in the lift pump seems to be mounted on the inlet side of the pump and opens by pushing the ball down into the motor cavity.

The relief valve actually operates opposite of how you are thinking. The ball in the relief valve has a spring on top of it to keep it seated in the down position. As the pressure from downstream builds up in the motor cavity and against the ball, it will eventually push the ball off the seat and let fuel pass back into the inlet of the pump. At this point you see the decrease in downstream pressure because the pump is in a recycling mode as it sends fuel through the motor cavity, through the relief valve and back through the pump again.



If the pump were dead and not turning at all, the vacuum from the vp would actually make the relief valve seat tighter.



I'm thinking that a dead lift pump will lead to a dead vp44 quickly because the vacuum needed to pull the fuel from the tank, through the dead lp and up through the filter will cause the vp44 to cavitate and destroy itself.



Greg

 

[Gary - K7GLD]

The relief valve actually operates opposite of how you are thinking. The ball in the relief valve has a spring on top of it to keep it seated in the down position. As the pressure from downstream builds up in the motor cavity and against the ball, it will eventually push the ball off the seat and let fuel pass back into the inlet of the pump. At this point you see the decrease in downstream pressure because the pump is in a recycling mode as it sends fuel through the motor cavity, through the relief valve and back through the pump again.



If the pump were dead and not turning at all, the vacuum from the vp would actually make the relief valve seat tighter.



I'm thinking that a dead lift pump will lead to a dead vp44 quickly because the vacuum needed to pull the fuel from the tank, through the dead lp and up through the filter will cause the vp44 to cavitate and destroy itself.



Greg

YUP - Greg has it right!



The INLET side has NO pressure - all the system PSI is on the OUTLET side - which then creates pressure thru the motor housing, and if it exceeds the spring pressure holding that ball on it's seat, it opens - allowing excess fuel PSI to be returned to the lower PSI inlet side and then recirculated thru the pump section.



Greg also is correct about a stalled LP placing deadly restriction upon the VP-44 - which is why I always add an external automatic bypass valve AROUND the LP - to open up if the LP stalls or fails, and allows near-normal fuel flow AROUND the pump to keep the VP-44 supplied.



Here's a pic of one of those added bypass valves as installed on my current Walbro which will ALSO starve the VP-44 if it fails or stalls, and the Carter pump placed further on down the line which has it's own automatic bypass valve installed.



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In the above configuration, the Carter pump is not connected to power, it's purely there for backup in case the Walbro fails - and if it does, in just a couple of minutes I can switch the power lead from the Walbro over to the Carter and continue on down the road. As it is, the Walbro is pumping AROUND the Carter thru the Carter's own added bypass, and if I need to switch pumps, the Carter will SUCK fuel from around the stopped Walbro.



It's been fully tested, and works exactly as described...

 

[GHolcomb]

Gary, you didn't say this but I would say that you have a check valve in your by-pass to keep the fuel from flowing backwards and recirculating through the lift pump?



If so, is that similar in design to the regulator that you have installed on your truck?



I think the by-pass is a good safety precaution and could save the vp44 if a lift pump goes down and you don't notice it immediately.





Greg

 

[Gary - K7GLD]

Gary, you didn't say this but I would say that you have a check valve in your by-pass to keep the fuel from flowing backwards and recirculating through the lift pump?



If so, is that similar in design to the regulator that you have installed on your truck?



I think the by-pass is a good safety precaution and could save the vp44 if a lift pump goes down and you don't notice it immediately.





Greg

Yes, it is a one-way valve - fuel flow is blocked in the reverse direction as long as the pump is operating normally, but opens if normal flow is lost.

 

[Misenheimer]

Oh well

I got the idea that it was like this from going in the inlet side with a pick and pushing the ball into the motor cavity. I also blew the picture up 400% and thought that I saw a spring on the motor side.



Sorry about that

 

[Gary - K7GLD]

Oh well

I got the idea that it was like this from going in the inlet side with a pick and pushing the ball into the motor cavity. I also blew the picture up 400% and thought that I saw a spring on the motor side.



Sorry about that

NO sweat - the primary value of boards like this to most members, is to both learn, and SHARE what we learn. Just about the time I get arrogant enough to think I have most of the answers, a new lesson pops up and hits me between the eyes! :-laf