Engine/Transmission (1998.5 - 2002) upside down lift pump

[Fishin Guide]

Yeah, I was just tryin to be funny.



I have lowered the amount of vacuum I pull by doing the Draw Straw and big line to the inlet of the pump. Since fuel pressure went from 22psi to 37 psi at WOT, I know it did some good. Also, it would bury a vacuum gauge at idle with the stock module.



I would have no doubt that cavitation or more likely, aeration was taking place in my old setup. I know I have good clean flow as I have checked it against a head pressure like Gary has with clear tubing.



Gary is right. The entire fuel system has points that could be addressed. I think by looking to the simple is better thought process, we could solve lots of these issues.



However, the stock pumps are not exactly the best for the job. If the factory really wanted to do us a favor, they would have put large pumps in the tank from the beginning. They could bypass excess pressure into the tank and use the fuel for a heat sink.



Now we have to pull some of that fuel up and out of the tank. Even though a partial siphon helps, there is no getting around the fact that those tiny module fittings only flow so much fuel at a given rate.



But I am geting off track. This situation sounds like the pump is bad. I had exactly the same thing going on and thought I was sucking air. Turns out the internal bypass could not reseat itself and raise pressure unless I floored it taking the fuel pressure off the bypass. It would reset and might be fine for a while, but usually would repeat this process. New pump, issue gone.



I am not saying cavitation is not happening. Especially after having a module apart. But, I just don't think that's the underlying cause here.



JMO



Dave

 

[BTowler]

On a cam driven pump, those are pullers, not pushers. Electric pumps are pushers... ever see an ols ford with a cam fuel pum on the engine? Puller...



I hae a FASS located on the rame by the tank and have 15 psi and that is regulated. I don't see less than 12 when full throttle. 15 at idle and cruise... has been on over a year and no problems. only runn the fass and no carter pump.



Gary, am I right that the 10 micron filter on the fass is the same size for the stock canister? I still use the canister but I heard it was not needed. . that true? and how long should I go on the FASS filter miles wise?

Whether a pump is mechanical or electric has nothing to do with being a pusher or puller. That is dictated by pump location and whether it is flooded or has to draw head. To say that placing the pump closer to the tank makes it a pusher is incorrect also, it still has to draw head to get the fuel, but it has less distance, reducing the work it has to do. If it was fed from a wet sump it would then become a pusher since it is getting pressure at the pump due to gravity feed.

 

[Gary - K7GLD]

OK perhaps not as laboratory-like as some might insist upon - but here's a video example of cavitation in action - focus on the PSI in effect, not the method it was obtained - it all works out the same, whether the PSI is obtained while the pump is installed on the engine, or on a test bench...



Click here to watch Cavitation



It's worth mentioning that even with NO restriction related to clogging, kinked lines or others, these Carter pumps WILL cavitate at 15 PSI or so, even if the OEM system is relatively free and open - the solution is to either provide for better overall system flow, or provide a method to reduce overall system PSI to some point BELOW 15 PSI or so, such as a PSI regulator. The pump used in my video demo has operated flawlessly on my truck for 50K miles - but the rest of my system has enough mods to not allow cavitation problems - that same pump pictured will operate pretty much endlessly down at 12-13 PSI - but you can see what another 2 PSI causes to happen!

 

[dsherman]

OK perhaps not as laboratory-like as some might insist upon - but here's a video example of cavitation in action - focus on the PSI in effect, not the method it was obtained - it all works out the same, whether the PSI is obtained while the pump is installed on the engine, or on a test bench...



Click here to watch Cavitation



It's worth mentioning that even with NO restriction related to clogging, kinked lines or others, these Carter pumps WILL cavitate at 15 PSI or so, even if the OEM system is relatively free and open - the solution is to either provide for better overall system flow, or provide a method to reduce overall system PSI to some point BELOW 15 PSI or so, such as a PSI regulator. The pump used in my video demo has operated flawlessly on my truck for 50K miles - but the rest of my system has enough mods to not allow cavitation problems - that same pump pictured will operate pretty much endlessly down at 12-13 PSI - but you can see what another 2 PSI causes to happen!

Gary,

Really a nice job testing that pump

 

[GHolcomb]

Hey Gary... nice job! That looks like one of my experiments!



Here is a technical definition of cavitation that may help. I didn't realize that you could have "Suction" cavitation as well as "Discharge" cavitation. Both conditions can exist for the LP as Gary has stated.



Suction cavitation - Input side is restricted

Suction cavitation occurs when the pump suction is under a low pressure/high vacuum condition where the liquid turns into a vapor at the eye of the pump impeller. This vapor is carried over to the discharge side of the pump where it no longer sees vacuum and is compressed back into a liquid by the discharge pressure. This imploding action occurs violently and attacks the face of the impeller. An impeller that has been operating under a suction cavitation condition has large chunks of material removed from its face causing premature failure of the pump.





Discharge cavitation - Output side is restricted

Discharge cavitation occurs when the pump discharge pressure is extremely high, normally occurring in a pump that is running at less than 10% of its best efficiency point. The high discharge pressure causes the majority of the fluid to circulate inside the pump instead of being allowed to flow out the discharge. (kind of like a blender) As the liquid flows around the impeller it must pass through the small clearance between the impeller and the pump cutwater at extremely high velocity. This velocity causes a vacuum to develop at the cutwater (similar to what occurs in a venturi) which turns the liquid into a vapor. A pump that has been operating under these conditions shows premature wear of the impeller vane tips and the pump cutwater. In addition, due to the high pressure conditions, premature failure of the pump's mechanical seal and bearings can be expected. Under extreme conditions, this can break the impeller shaft.



However... with all of our new found understanding of cavitation... I still think there is also something is going on with the electric motor. I think I am going to try a set up like Gary's and see if I can find variation in the motors.



I know there are several good fixes for this problem out there, but I am just curious about what all the failure modes are for that pump!



Greg

 

[EricBu12]

Btowler,



my understanding is that a mechanical pump can pull more than it can push, with the lifting action of the cam... that's why EVERY mechanical pump is on the engine. . that's the design.



EVERY car out now has a small electric pump because they push better than they pull. that's why a lot of them are IN or NEAR the gas tank.



DC decided to mount an electric pump where the old mechanical pump used to be... this is lazy engineering. now they have an in-tank electric pump... took awhile for them to wise up... .



I have the FASS and yes it can pull but the siphon action helps it and the return from the regulator keeps a small head pressure to keep the pump from working too hard... So far,... 0 problems!... good pressure, good flow, no problems with my VP44 after 82K miles and mods to total 400 hp.

 

[Gary - K7GLD]

I have received a followup PM in regards to my above LP test video - and the questions and comments it presents are worth sharing with the rest of the members:



=====

Hi Gary,



I posted a response to your video, but I wanted to get your thoughts on a couple more questions.



1. With a LP that starts out at 15 psi, goes into cavitation, pressure drops to 3 psi... what happens as you slowly release the restriction? Your video cut that part just a bit short, so I am wondering if the pump ever recovers to a smooth pumping state? I am thinking this would simulate going from idle to higher rpm where there is more flow required.

USUALLY the PSI will rise back to it's "normal" value when PSI/flow is restored - BUT, it's not uncommon for the cavitation air blockage to NOT allow restoration of PSI, and the pump must be completely shut down and restarted for normal operation to resume - in fact, that was EXACTLY what happened in my demo, and that's why there was a break between the first and second section of the cavitation demo - the pump would not resume proper operation when I removed the restriction, and I had to shut it down to continue the demo.

2. Where could there be a restriction on the output side of the LP if you are reading 15 psi on the output side of the fuel filter? From there it goes straight into the injector pump. I'm thinking that the cavitation you demonstrated on the bench may be for pumps that will actually reach 15 psi, but if you have a pump that tops out at say 13 psi, it will not cavitate. What I am saying is that maybe there is not a restriction on the output side, it's just that the pump is capable of 15 psi at idle, which in turn leads to cavitation. Bottom line is back to your point, the pump is not a good fit for this application.

The VP-44 itself is a "restriction" down at low RPM (idling) engine operation - and the actual PSI seen back at the LP can easily be at the threshold of cavitation under those conditions - especially if assembly tolerance of a specific LP bypass valve places it's bypass PSI at some value ABOVE 15 PSI. BUT, you are correct - if the pump will only see a PSI of 13 or so, danger of cavitation is reduced - too bad the bypass section of these LP's isn't adjustable!

3. What happens on your bench test when you install the "by-pass"? If you put the pressure gage after the by-pass, what is the initial downstream pressure and then I would love to see what happens to that pressure as you crank down on the clamp. I would expect that you would not see cavitation and the sudden drop from 15 psi down to 3 psi. My guess is that you may not see the 15 psi initially either.

If the operating PSI of the LP is reduced by ANY method to a value below it's natural cavitation point, it will not cavitate.

I have two pumps I want to test. One demonstrated exactly the same characteristics as your bench test. The second one came off my brother's truck and it was registering 0 psi at idle and negative pressure at higher rpm. New LPs were installed in both cases and the situation was remedied. I now realize that at least one of the pumps is probably still good, not sure what is up with the other one.

 

[BTowler]

Btowler,



my understanding is that a mechanical pump can pull more than it can push, with the lifting action of the cam... that's why EVERY mechanical pump is on the engine. . that's the design.



EVERY car out now has a small electric pump because they push better than they pull. that's why a lot of them are IN or NEAR the gas tank.



DC decided to mount an electric pump where the old mechanical pump used to be... this is lazy engineering. now they have an in-tank electric pump... took awhile for them to wise up... .



I have the FASS and yes it can pull but the siphon action helps it and the return from the regulator keeps a small head pressure to keep the pump from working too hard... So far,... 0 problems!... good pressure, good flow, no problems with my VP44 after 82K miles and mods to total 400 hp.

Actually, mechanical pumps are on the engine because they need an external source to power them, if you put a motor on it, then it becomes an electric pump. They also are not usually impeller pumps. I should have stated that the pump design itself has a major bearing on push/pull ability. An impeller pump is better at self priming, but still has head issues to deal with, which can be overcome by proper sizing as in your FASS. A piston pump generally can't self prime and is not good at drawing head, some can't no matter what without assistance, but can generally produce much higher pressures. Any time you reduce the distance a pump has to draw it will work more efficiently, pusher or puller.



I deal with pumps all the time, I have my own brand of Misting Systems and assemble pump units that run 800-1200psi, flow . 5-5gpm, rated from 12-24 hour duty cycle. Hmmmm... I wonder?:-laf

 

[WyattEarp]

How hard is it to move that LP to the frame or lower than where it is now? My Lp went and my Inj. pump went about a week ago, im attempting to fix it myself, seems pretty straight forward, just wondering while im fixing what else i can do as far as preventive maint. moving that lp closer to tank or simply putting it lower than current locations.



Thanks

 

[GHolcomb]

You can get a nice relocation kit from Geno's Garage made by Vulcan. This puts the lp down on the frame and closer to the tank.



You should look at the "Cavitation is not your vp-44's friend!" thread. There are some good pictures of what other guys have done in relocating the lp, creating a by-pass and installing other brands of lift pumps.



Greg

 

[JKinney]

How hard is it to move that LP to the frame or lower than where it is now? My Lp went and my Inj. pump went about a week ago, im attempting to fix it myself, seems pretty straight forward, just wondering while im fixing what else i can do as far as preventive maint. moving that lp closer to tank or simply putting it lower than current locations.



Thanks

I moved mine to the frame a couple years ago, As others have posted each pump lasts about a year and then cavitation starts, ie: cruising at 70 mph fuel pressure sitting on 12 psi as it has for a year and then you glance at the guage and it sais 6 psi (cavitation). Put on a new pump runs great numbers then cavitation. I just installed a walbro with bypass.

 

[PAckley]

I lost a vp44 just after installing an Edge system and noticed the stock fuel pressure dropping below 5 psi at wot. I immediately installed a Vulcan big hose system, with relocated new Carter pump. It was too late, the VP44 failed from previous abuse. This was a used truck so prior history unknown.
I installed a HOVP44, which provides amazing power making the Edge stages used as much as the "hotrod" VP44 makes a striking difference.

The vulcan system would also give me situations where fuel pressure would drop below7 psi under wot. It always would be at 13 psi under idle.

I changed to the Glacier System with the Walbro pump. Now my idle pressure is 19-20 psi always. WOT is never lower than 13 psi. This has to be the best solution. Discussions about cavitation must be the issue with other style pumps.