2nd Gen Non-Engine/Transmission Walbro 392 pump - How much current does it take?

[rweis]

You guys that are running the Walbro 392 inline pump.



What kind of current does that pump take to maintain 14 psi to the VP44? I can not find the answer anywhere.



When I find a Walbro current vs fp graph, to pump 45 gph the current seems to be 11 amps, but the psi is 77 psi (a "tad" high). I must not be reading the graph right I think. When I read 15 psi it is at 20 gph, not enough to properly feed the VP44.



Confused



Bob Weis

 

[rweis]

Well, the purpose of the question is because I am going to change the OEM carter the RASP uses as a backup to the Walbro 392. BUT, Gary has a good idea, that instead of running this pump wide open then trying to do something with the heavy output, to manage the pump to a level that it is producing what the VP44 needs plus a little bit.



The PWM (Pulse Width Modulator) we had been using on the VP44 blower is rated at something like 7. 5 amps max. I was trying to findout if the Walbro 392 was in that range. I think it is not.



I dug around the internet and found a more commercial PWM that will manage 15 amps that should do the trick. Mount the rheostat in the cab (Gary's idea) so you can dial in the psi you want for the load condition you have rather than run the pump wide open and try to deal with the high output.



I do not think the RASP should ever fail, BUT if it does I do not want my VP44 at the mercy of an OEM Carter that may or may not function correctly, when I can emergency shift to a much higher quality electric pump that I can manage the output psi the VP44 sees from the cab.



I would still like to know what the Walbro 392 needs as far as amps to double check the value I read in the pump graph data.



Bob Weis

 

[NoSeeUm]

Bob, I don't know how many amps. But GD does sell a nice relay with OEM connectors. It takes all the load off of the ECM.



You can make your own for cheaper, but this is the one I used.



Jim

 

[Bob4x4]

I don't think I would try to use pwm to drop a 90 psi pump down to 15psi. Just run a regulator to return the excess psi back to the tank.



Bob

 

[Gary - K7GLD]

I don't think I would try to use pwm to drop a 90 psi pump down to 15psi.

Bob

Not sure I would either - but who has proposed that?



For my part, I'll probably end up using a PWM to drop system PSI to about 25 PSI, and then use my regulator to bypass excess PSI above 18 PSI or so as measured right at the VP-44 under the heaviest load I can place upon it.



As far as running the Walbro wide open, and then passing over 50% of it's output back to the tank, there's been enough scattered related problems reported with fuel foaming and air in the lines, fluctuating PSI and such, to convince me that vastly too much PSI and GPH isn't the way to go either...

 

[mmyers1]

Not sure I would either - but who has proposed that?



For my part, I'll probably end up using a PWM to drop system PSI to about 25 PSI, and then use my regulator to bypass excess PSI above 18 PSI or so as measured right at the VP-44 under the heaviest load I can place upon it.



As far as running the Walbro wide open, and then passing over 50% of it's output back to the tank, there's been enough scattered related problems reported with fuel foaming and air in the lines, fluctuating PSI and such, to convince me that vastly too much PSI and GPH isn't the way to go either...

OK, this thread is full of acronyms that I have not IDEA what they mean!! I got PSI and GPH... what are the others?



Thanks!



Mark

 

[Gary - K7GLD]

OK, this thread is full of acronyms that I have not IDEA what they mean!! I got PSI and GPH... what are the others?



Thanks!



Mark

Perhaps the acronym that you are unfamiliar with is "PWM" - or Pulse Width Modulator - which is an electronic device that essentially is capable of feeding a DC motor with adjustable "pulses" of power to change their RPM without creating excessive heat as would be the case if reducing voltage was used to vary RPM.

 

[mmyers1]

Perhaps the acronym that you are unfamiliar with is "PWM" - or Pulse Width Modulator - which is an electronic device that essentially is capable of feeding a DC motor with adjustable "pulses" of power to change their RPM without creating excessive heat as would be the case if reducing voltage was used to vary RPM.

That was definately one of them!! In an earlier part of the thread, you said:



For my part, I'll probably end up using a PWM to drop system PSI to about 25 PSI, and then use my regulator to bypass excess PSI above 18 PSI or so as measured right at the VP-44 under the heaviest load I can place upon it.



As far as running the Walbro wide open, and then passing over 50% of it's output back to the tank, there's been enough scattered related problems reported with fuel foaming and air in the lines, fluctuating PSI and such, to convince me that vastly too much PSI and GPH isn't the way to go either...



Can you explain this some more? You are an excellent teacher as is evidenced by previous threads you have been involved in. I am new to all of this, and as you have said, I want to avoid throwing money blindly. I have 109K on my girl. At your, and others recommendation, I have ordered a full compliment of gauges from Geno's (Westach EGT/Boost, Fuel Pressure, and transmission Temp w/A-piilar triple mount and speaker). Once I have these guys mounted, I am going to look at the alternatives for the LP. At this point, I am strictly stock, but who can say what is in the future! I would have put gauges in earlier, but was trying to avoid the DC warrantly 'Finger of God'!

At least until the warranty expired! I avoided Bio for the same reason... . I did not want to give them ANY excuses... .



Everything that those with experience can provide I appreciate. I just have to scale the info to my known variables and work within the confines of my situation.



Thanks again!!!



Mark

 

[Gary - K7GLD]

Can you explain this some more?

WELL, as good as the Walbro pump in particular seems to be, I'm sorta uncomfortable using a 110 PSI or so pump to supply a system that only requires about 13-15 PSI for normal operation - and then has to return a vast amount of unneeded fuel back to the fuel tank.



Instead, I plan to try installing a PWM to adjust the actual operating RPM and PSI of the Walbro down to a threshold point slightly above the volume/PSI the VP-44 actually needs for proper operation. Theoretically, this reduction in operating RPM and load on the Walbro pump would cause it to run cooler and last longer - always a worthwhile goal...

 

[mmyers1]

WELL, as good as the Walbro pump in particular seems to be, I'm sorta uncomfortable using a 110 PSI or so pump to supply a system that only requires about 13-15 PSI for normal operation - and then has to return a vast amount of unneeded fuel back to the fuel tank.



Instead, I plan to try installing a PWM to adjust the actual operating RPM and PSI of the Walbro down to a threshold point slightly above the volume/PSI the VP-44 actually needs for proper operation. Theoretically, this reduction in operating RPM and load on the Walbro pump would cause it to run cooler and last longer - always a worthwhile goal...

Thank you! Is there a specific manufacturer/model you are looking at, or are you going to home-brew one?



Thanks!!



Mark

KE5APN (just as unhandy with HAM as I am with CTD!)

 

[Gary - K7GLD]

Thank you! Is there a specific manufacturer/model you are looking at, or are you going to home-brew one?



Thanks!!



Mark

KE5APN (just as unhandy with HAM as I am with CTD!)

Mine is a kit, available thru:



Kitsrus.com Main page



Kit #67 - I believe they may also offer it as a wired assembly. but it's not hard to assemble. If you do an Internet search for "PWM kits", you will get a few other vendors as well. This will be my second use of one of these, the first one is used to control blower speed for cooling my VP-44, and looks like this as assembled and installed on my truck - the assembly on the left:



#ad




Since I have these installed in my engine compartment, I have them individually enclosed in Radio Shack boxes that I have drilled for ventilation:



#ad

 

[GHolcomb]

Has anyone tried grabbing the RPM signal and using that to vary the voltage to the LP? This would make the LP act like a mechanical, cam driven LP. High flow at high RPM, low flow at low RPM.



Greg

 

[Gary - K7GLD]

Has anyone tried grabbing the RPM signal and using that to vary the voltage to the LP? This would make the LP act like a mechanical, cam driven LP. High flow at high RPM, low flow at low RPM.



Greg

Sorta depends on your target PSI at the extremes - the lower PSI is easy enough with the OEM LP's, but the high end will never go above 15 PSI or so - you'd get better "overhead" and room for adjustment with something like the Walbro that has enough capacity to work across a larger spread.



Personally, I have no problem with any steady PSI below 20 or so, and 12-15 is even better... Less complicated, too! :-laf

 

[BTowler]

Gary, if I remember correctly, what you are proposing will also reduce the gpm rating of the pump as well.



Also, I have not seen any of the negatives you have reffered to, and have been running a Walbro for over 6 months now.

 

[Gary - K7GLD]

Gary, if I remember correctly, what you are proposing will also reduce the gpm rating of the pump as well.



Also, I have not seen any of the negatives you have reffered to, and have been running a Walbro for over 6 months now.

It's true the GPH will be reduced - but available flow down at the PSI required by the VP-44 is WAAAYYyyy more than needed. As to "negatives", I get on several other boards besides this one, and HAVE seen several issues related to the large volume of fuel that necessarily MUST be bypassed on 2nd generation, VP-44 equipped trucks.



Here on this board, there are a few Walbro failures - and while the ones I point to here were not apparently directly related to flow issues, they WERE failures :



https://www.turbodieselregister.com...missions-2003-2007/180381-walbro-failure.html



Nothing to get terribly overwrought over I suppose, but since I like to experiment anyway, reducing the Walbro output to bring it more in line with my actual needs seems a good place to start. My comments concerning the Walbro are more as an observation, rather than a criticism...

 

[BTowler]

If it works, let me know.

 

[Gary - K7GLD]

We were both posting at the same time - I had edited to include a thread on Walbro failures:



https://www.turbodieselregister.com...missions-2003-2007/180381-walbro-failure.html



It will probably be a few weeks before I get my PWM kit assembled and installed - I want to get some good baseline data on the Walbro installed at full DC power anyway, so no big rush - so far, the Walbro is functioning perfectly - and I'd have NO qualms at just continuing to run it as it is...

 

[LKothe]

Walbro 392

I purchased the Big Dog kit from Wide Open Diesel, installed it and regulated my pressure down to 18#. It works great returning the excess to the tank. Not only do you have a real consistent pressure to the V-44 but the fuel returning to the tank tends to warm the fuel in the tank. I believe this will help the fuel heater after running the truck for a while then shutting it off to restart later. I've noticed my heaters do not come on after running the truck for a while. Plus, if you need extra fuel, the regulator is simple to reset. The only drawback that I have seen is that if you trottle it fairly hard while the engine is cool, the pressure will drop somewhat. Once the fuel has returned for a short time, it's 18# whatever I do to it.