Engine/Transmission (1998.5 - 2002) Walbro flow rate, Amprage draw (14 PSI)

[Gary - K7GLD]

In another related thread, Bob Weis was considering use of a Walbro GSL-392 fuel pump, and asked as to "real world" flow rate at a nominal 14 PSI, as some use as a target PSI with the required bypass regulator.



Since I have a spare 392 waiting installation, I decided to fabricate another working complete system, including the automatic flow bypass I use on all my own installations, and a regulator/bypass that returns unused, excess fuel PSI back to the fuel tank. I got all that assembled, then set it up on a test bench for a "live" test:



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The operating PSI looked like this:



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Right on target!



Set up as above, the fuel flow worked out to 1 gallon in exactly 45 seconds - 80 GPH, and the amp draw was measured at slightly over 6 amps. Here's the Walbro flow/PSI/amp chart for the 392:



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All the above was interesting to me - I had assumed current draw was in the 5-7 amp range, which is well within the 20 amp contact rating of the control relay I use in my setup - glad to see my assumption was right!

 

[RJWEST]

Great,,,
?? The can at bottom was the " Tank " ???

?? The pump picked up the fuel from a dry state ??
IE: Lot's of suction

 

[Gary - K7GLD]

Great,,,

?? The can at bottom was the " Tank " ???



?? The pump picked up the fuel from a dry state ??

IE: Lot's of suction

YUP - the 5 gallon can was the supply - and yes, the Walbro primed itself and ran flawlessly - MAN these things are QUIET!



I didn't have enough hose to raise the tank higher, and if anything, the Walbro would perform even better at a lower location, such as many of us do by mounting pumps back on the frame rail right close to the tank...

 

[RJWEST]

Thanks, Looks Like i'm headed in that direction...

I have a GM type solenoid LP, May use it as a check valve,
emergency pump,
It seems to be directional.
Less Pressure , but ok for low power emergency...

 

[rweis]

I have done some research on internal gear pumps (gearotor) and external gear pumps (parallel gear mesh type (RASP, Fuel Boss, MITUSA) and they generally can lift (suck) a pretty long way, ESPECIALLY if they have ANY fluid or moisture in them. Most of the tolerances are . 0005 (1/2 of a thousanth).



One I am particularly researching:



RPM Speed to 900 RPM (You slow it down to get the GPM you want)



Pressures to 200 PSI



Flow rates to 26. 8 GPM (300 RPM = 1. 4 GPM @ 50 psi 0. 10 HP motor required)



"Suction Lift: Up to 28" Hg / 31 feet depending on the type of liquid being pumped. " Would not have to mount this thing down on the frame rail to pickup fuel. How about mounting you fuel pump where ever you want. What a novelty!



It can pump 32 SSU to 100,000 SSU. Diesel is 39 SSU, 100,000 SSU is like molten lead. Will tolerate 25 micron size particles. Self lubricating using the pumped liquid.



It is physically small: 3. 00 Wide, 3. 69 High, 6. 25 Total length including the shaft. Foot mounting



You can get Rebuild kits, Gear sets, Bearing sets, Seal kits. Basically you can rebuild the pump to a like new condition. You can also send it back to the manufacturer and have them rebuild it for you.



There are some interesting possibilities out there. Just have to find the one that is most correct for our application.



Bob Weis

 

[RJWEST]

Gary/Bob, another question.

With the Walboro, what happens if the Pressure Relief
sticks closed, will the pressure Kill the VP44
I have a feeling the VP44 Bypass valve can not return enough
Fuel to keep the pressure down... ?
( Bob, I know thats not a problem for you with 2 relief valves )

I know, a little late to the table, but I'd like to only redo the fuel
system 1 more time...

? Would you need a high pressure sw to turn off the LP, ?

 

[Gary - K7GLD]

Gary/Bob, another question.



With the Walboro, what happens if the Pressure Relief

sticks closed, will the pressure Kill the VP44

I have a feeling the VP44 Bypass valve can not return enough

Fuel to keep the pressure down... ?

( Bob, I know thats not a problem for you with 2 relief valves )



I know, a little late to the table, but I'd like to only redo the fuel

system 1 more time...



? Would you need a high pressure sw to turn off the LP, ?

Pretty unlikely mine would stick, but yes, if it stuck closed, WAYYYYy to much PSI at the VP-44!



I suppose a person COULD install a "too high" pressure switch - but probably overkill...

 

[rweis]

Well, the pressure relief brass bypass is a mechanical spring loaded cone against a sealing surface. If the pressure started to increase it would put even more pressure on the face (pointy) end of the cone. Short of the cone jambing cockeyed in the relief valve internal cavity I am not sure it could even happen.



This is one of the reasons to go with the Kinsler bypass valve. The design of the inside cone has a lot of cylinder length to assure alignment before it is shaped into the sealing cone shape. The actual fuel bypass of the cone is not down the sides of the cone between the cone and the sides of the valve body, but through holes around the perifery (sp) of the cone shape head just below the metal to metal seal and the fuel is directed into the center cavity of the valve.



Think of the valve as a bullet mounted into a very close fitting cylinder. The bullet nose is pressed up into a sealing surface of the valve body (where the bullet nose meets the body of the valve) by the spring under the bullet nose. The spring seats up into a cavity inside of the bullet nose so the spring maintains parallel alignment and centered with the valve body. The other end of the spring sits in the inside cylinder of the valve with the far end flat of the spring sitting on a 1/8" wide ledge (ie pleanty of ledge for the wire spring to sit parallel to the inside valve body) that has the outlet flow into the AN-6 male fitting machined into the valve body. The bullet nose is about 1/2" long so it stays aligned with the inner cavity of the valve body. The bullet nose has bypass holes in it that bypass the fuel into the center cavity of the valve body. As soon as the input fuel on the bullet nose overcomes the spring tension and starts the bullet nose to travel down the valve cavity the holes that are just slightly further down the bullet nose than the sealing surface are now exposed and start bypassing fuel into the center of the cavity relieving the pressure on the bullet nose.



One of the reasons I went with the Kinsler bypass valve is they are designed to withstand like 60 psi opening pressure. Our requirement of 13. 5 psi is almost trivial to the design characteristics, and the first one I ordered they thought I had gotten the psi wrong or they had written it down wrong, huh? 14 psi?, you mean 64 psi don't you?



The Kinsler units are very well made and function very well for the couple of years I have run them. Whenever I have had an occassion to open the Kinsler bypass I look for scratches or any deterroiation of any kind and have never found even the slightest deterroiation of any kind.



The DTT bypass is designed pretty close to the same, but I could not get different spring sets and shim sets so I could get exactely the repeatable psi I wanted. The Kinsler springs do not fit quite right into the DTT bypass body. The spring flat end does not sit as parallel inside the DTT body, and I did not want any possibility of the spring getting cocked off to one side and causing the very problem you bring up.



I use parallel bypasses so the spring travel is more linear and over a shorter distance and is more repeatable. I guess it is also a backup in your scenario, but that was not the primary reason I went that way.



Bob Weis

 

[rweis]

The VP44 outflow bypass is almost tiny in comparison. The VP44 outflow "bypass" is comprised of two bores. A throttle bore about maybe (guessing) 1/32", and a bypass bore about maybe (guessing) 1/8". The input to the VP44 "bypass" valve from the VP44 side of the valve about maybe (guessing) 1/4".



The guesses are based on looking at the picture of the VP44 outflow valve in the Bosch "Distributor-Type Diesel Fuel-Injection Pumps" 2003 edition of the Bosch Yellow Jackets series and equating the picture size to the physical size.



No the VP44 outflow "bypass" valve could never handle the Walbro 392 flow. Neither could the fuel return lines to the tank either.



Bob Weis

 

[Gary - K7GLD]

About the only scenario I can visualize for the bypass/regulator to get stuck closed would be in freezing weather - but in that scenario with gelled or freezing fuel, I'd suspect enough other related fuel system issues as to substantially outweigh the regulator itself.



In any event, and with our own winter zero degree weather, placing mine underhood next to the engine is probably the best insurance against it freezing up as is readily available:



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Some guys place theirs back under the truck bed, near the fuel pump - but that area also sees lots of unprotected exposure to cold air movement in cold weather - and greater potential for freeze-ups...

 

[ERuhl]

No the VP44 outflow "bypass" valve could never handle the Walbro 392 flow. Neither could the fuel return lines to the tank either.

I'm using only the stock return line for mine. I Tee'd the Mallory return into the stock return, and seems to work just fine as far as I can tell. Is there something I should be concerned about?

 

[Gary - K7GLD]

I'm using only the stock return line for mine. I Tee'd the Mallory return into the stock return, and seems to work just fine as far as I can tell. Is there something I should be concerned about?

The size of that OEM return line is pretty marginal to handle both the VP-44 returned fuel, as well as the additional excess the Walbro 392 pump puts out in a typical install - dunno about other brand pumps...

 

[NoSeeUm]

I'm using only the stock return line for mine. I Tee'd the Mallory return into the stock return, and seems to work just fine as far as I can tell. Is there something I should be concerned about?

I used a separate line and tee'd it into the tank fill hose. This was just my mind set when I did the install. No particular reason really other than I felt the Walbro would be recirc allot at idle and I wanted to make sure I had no back pressure on the OEM return line. In your case, I would think that if it is working, then it is working!



Jim

 

[rweis]

Well, depends where you T it in.



At the engine T:



The VP44 and the injector drain line meet at the engine T inputs. The output leg that goes down to the frame is a flex tubing inside of a rather large rubberized loose sheath.



The output of the engine T is 1/4 steel tubing that is double swegded and a nylon line fits INSIDE of the 1/4 tubing. The tubing is like the tubing that is on your refridgerator water line just smaller and I am sure a different material.



The nylon line fits INSIDE the 1/4 OD and like 7/32 ID tube. The nylon line has wall thickness of about 4/32 (total for both sides of the nylon tube) leaving about 3/32 to 4/32 (1/8) for the ID of the nylon flex tube where your cooling fuel returns to the tank.



Then the nylon flex tube goes down to the steel fuel return line and fits INSIDE the steel return line.



IF you T'ed the steel line you should have enough ID to work with.



IF you T'ed into the VP44 line before the engine T, if might be iffy.



I do not remember where, somewhere on TDR I remember several years ago that the VP44 return line should NOT have more than 10 psi in it. Of course it dumps back to the tank cannister and should be at zero psi, but ??? A couple of guys (me included) have replumbed from the engine T back to the tank. I did mine by cutting the double swege off the return leg of the engine T and puting that tube INSIDE a AN-6. 3 small hose clamps (remember no psi), done. I run mine back through 4 fuel coolers to get the VP44 internally generated heat out of the fuel before it goes back into the tank.



I also run my VP44 major fuel bypass back to the tank in a DIFFERENT line, just so I know the VP44 return is not competing with anything else to get the fuel back to the tank.



Bob Weis

 

[rweis]

Thanks Gary, I think there are enough Walbro 392's out there to give it a try. Appreciate the test bench workup, actually better than I expected it would be. See comments about fluid lift capability above. I bet the Walbro could lift maybe 5' - 10' pretty easily.



IF you want to see what it will lift and it is not at least 5' - 10' I'll send you mail for a 6 pack of your choice. I am pretty confident that GOOD internal or external gear pumps can do WAYYYYYYYYY more than we think. See above (31' of verticle lift) on the industrial external gear pump I am looking at as my RASP replacement if the RASP (75k and still pumping right along) ever fails. It may be a project that never needs to be done



Bob Weis

 

[ERuhl]

Well, depends where you T it in.

At the engine T:

The VP44 and the injector drain line meet at the engine T inputs. The output leg that goes down to the frame is a flex tubing inside of a rather large rubberized loose sheath.

The output of the engine T is 1/4 steel tubing that is double swegded and a nylon line fits INSIDE of the 1/4 tubing. The tubing is like the tubing that is on your refridgerator water line just smaller and I am sure a different material.

The nylon line fits INSIDE the 1/4 OD and like 7/32 ID tube. The nylon line has wall thickness of about 4/32 (total for both sides of the nylon tube) leaving about 3/32 to 4/32 (1/8) for the ID of the nylon flex tube where your cooling fuel returns to the tank.

Then the nylon flex tube goes down to the steel fuel return line and fits INSIDE the steel return line.

I first removed the plastic return line that runs from the hard line at the back of the head down to the hard line on the frame rail. Mine is a late 02 (non-disconnect version of the front D60) and I honestly don't recall this being a very small tube like you describe, in fact I remember it being a lot like the supply line that I replaced between the frame and the factory lift pump (now the Mallory regulator) back when I swapped out all the banjos for AN fittings. The hose I remember looked like it was a shrink-fit install on the outside of the hard line, not on the inside. It's been a little while, so maybe I'm confusing the two? I do seem to recall fighting a quick disconnect at the upper end of the plastic return line? Anyway, whatever it looked like, I removed the plastic line and replaced it with -6 hose clamped on the hard line at the head and the hard line at the frame, and tee'd into that using AN fittings. I used the factory hard line on the frame rail back to the tank where again it switches to rubber hose to get back up to the fuel tank module.

A couple of guys (me included) have replumbed from the engine T back to the tank. I did mine by cutting the double swege off the return leg of the engine T and puting that tube INSIDE a AN-6. 3 small hose clamps (remember no psi), done. I run mine back through 4 fuel coolers to get the VP44 internally generated heat out of the fuel before it goes back into the tank.

Sounds like we did the same thing, except that I reused the hardline on the frame versus the fuel coolers.

I also run my VP44 major fuel bypass back to the tank in a DIFFERENT line, just so I know the VP44 return is not competing with anything else to get the fuel back to the tank.

My original plan was to run the Mallory return in its own line back to the tank (I was going to use the capped auxiliary port), but once I mounted the Mallory in the factory lift pump location that plastic return line was right there and replacing that made for a much simpler and cleaner install. The factory hard line and the -6 hose seem (IMO) plenty big to supply the return flow from the Walbro. When I first primed it (bump the key, engine off) I had the Mallory set as low as it would go and I saw well below 10psi on the gauge. Since the engine wasn't running, all the fuel was going back the return line at well under 10 psi, so it seems I'm ok. I promptly adjusted it up to 15psi idle and didn't pay much attention to what the unrestricted return pressure was, I just remember it was "very low". I suppose it's easy enough to repeat the test and see, that's where an externally-adjustable regulator shines

 

[NoSeeUm]

My Mallory is mounted on the frame with the WalBro.



I notice allot more interest in the 392, vice 391 (like mine). Any reason besides availability? Overkill?



WalBro Curves



I run Mach 4's and a TST, plus the Mallory regulator and I cannot pull my fuel pressure below 14 psi (AN -8 hose and fittings). According to the curve the 391 is making 50 gph @ 15 psi. The VP44 is pulling 45 gph at max fueling / rpm?



Jim

 

[NoSeeUm]

I must have jinxed myself. Just about no sooner had I typed the above message that I was driving home. I looked down and my fuel pressure was acting up. I even pulled the pressure to zero once. Amazing how fast I re-aquired the nervous twitch of looking at fuel pressure almost as much as looking at the road. Holy Cow!



The weather was pretty cold here and I had just bought some diesel from my not regular station (Fred Meyer). The tank was currently about 3/8 so I added a cup of PS winter formula. Much much better, but still pulling fuel pressure below 10 psi. I was starting to think that maybe the regulator was sticking.



Replaced the fuel filter, no change.



Cleaned my pump suction strainer and the problem appears solved.



I did notice a small amount of metal and plastic finds that refused to blow out of the strainer. Those would have have been pretty hard on the GS391. Glad I put the strainer in.



Odd though that nothing really indicated much plugging in the strainer. So I am not sure what exactly plugged me up. Some kind of diesel goop / slime that I couldn't see well. Not that I can ever see well these days. I am just glad that it is working normal again.



My fuel pressure is back to 16 psi idle and 14 psi WOT.



Jim

 

[gtwitch]

Gary, Reading back to one of your old posts, Did you use the Walbro pump and how was its life. Do you know what the VP 44 flow requirement is (stock 99 truck) I know that later in this series that Dodge had not only a pressure requirement but a flow test vs time. I can't remember what this was. I am putting on my 2nd Holly blue but it is noisey!



gtwitch in Wyoming K7NOI ham call