I want all the ideas and input I can get on this, so don't hold back even if you don't consider yourself an expert.

Basically we run our fuel psi anyplace between 5 and 20 psi, depending on who you talk to. Our VP44's not only need enough fuel to supply the injectors but it also needs extra that will return to the tank to dissipate heat.

Now, that being established. The VP44 is designed to maintain an internal pressure of 14psi at all times during operation.

Now, I AM NO MECHANIC OR SCIENTIST, but I am a tinkerer and like to apply common sence to things. With this in mind, my common sence says that if the pump has to maintain 14psi to keep the engine running right, then how can we be running anything less than 14psi. Anything less and you are not keeping enough fuel supplied to the VP for it to maintain it's pressure.

To expand on this thought. If we also need additional fuel to flow through the VP and back to the tank for heat dissipation, then we need more then 14psi for a healthy VP. So it seems to me that in an ideal situation we need to maintain between 16 and 20psi at all times to ensure we are getting the most out of these pumps.

Now tell me if you agree or dissagree and why. I wanna know if I'm missin a part of this equation and if I'm not then we need to establish some more diffinitive guidlines for our fuel supply system.

 

That sounds about right. The thing that would have to be figured out is how many gph the vp 44 flows to the injectors and exactly how much is sent back to the tank. So what would have to be done is the supply it with 14 psi at all times....but if it sends 80 gph to the injectors (just a figure) and 15gph back to the tank(again just a number) then you would want a 95 gph pump that can put out 14 psi. See this is where I can see a benefit of the rasp pump. Regulate it at say...15 psi. That way it stays 15 no matter what, idle, 1500 rpms,3000 rpms. But as far as how much fuel is used for each function it would be variable as we slow down and speed up. now for a genset it would be easy to figure out as they stay at certain rpms for hours at the time. But it's a good question. That's my two cents, whatchya think?

 

I think you added more questions, thanks Phil. That's the kinda stuff I'm lookin for though, keep em comin.

 

I wish I could recall where I read it, but isnt TOO much pressure also bad. I read some where that over pressure can cause issues too with the VP. I need to spend some time trying to backtrack on my reading. I do know I talked with a performance tech a while back and he said flow is much more important for the VP than having high pressure readings. Mainly cause flow means fuel is there or it isnt. You can have a high pressure reading but that doesnt always mean the amount of fuel pumped is adequate. So like what Phil was saying about the Rasp pump and regulator does seem to make more sense.

 

To much psi is deffinately just as bad, if not worse then not enough.

I don't think flow is gonna matter much in this case though. GPH and psi in this case are gonna be tied to each other. When your talking about an opening of less than 3/8" on the incoming fuel side of the VP44 you have a pretty good restriction there. So in this case you can't have flow without psi, they go hand in hand. If we were talking about a larger diameter hole to flow through it would be more of a question, the larger the hole the more pertinent GPH would become. Hope I explained my train of thought right.

 

yes, to much pressure will cause hard start problems and eventually lead to tears in the diaphragm of the pump. But the thing is the flow must be there. I know that when you have flow you have pressure. I've got the questions...and a vague understanding for answers...but I'm no pro at this, hopefully one will chime in.

 

I dont claim to be an expert at anything....but, Im curious, where do you get the 14 psi figure from?

 

A year or so ago my truck was dead for almost a month with fuel supply problems. Dodge and Cummins both gave up and just wantred to throw parts at it, so me and the pulled every single part that touched fuel and re-built it from scratch, piece by piece. During all of this I was dealing with a local company that is a diesel injection shop and authorized Bosch re-builder. I was using them for questions and to test parts and pieces as we got to them. They are the ones that told me about the fuel regulator and holding internal pressure at 14psi. Also that a good number of VP44 cores they get in are completely fine. This regulator just goes bad, so they change out a $1400 part instead of a $14 one.

 

Well if this is true about the regulator, how does one know the difference and save themselves that unneeded cost or exchange of the VP?

 

I rigged up a tester. It was a 2" long pipe nipple, welded a nut to one end to screw the banjo bolt into and an air fitting in the other end. By setting the air compressor I could measure the psi it took to open it up. I only went through that much trouble because I was proving a point. Normaly I would just stick a nail in there and guesstimate it. If your gonna change the VP out anyway you also need to chenge this fitting. So if your having VP problems just try the new one and see if it fixes it. It's less then $15 from the dealer, takes 10 minutes to change and your gonna need it anyway when you change the pump.

How many times on these boards have people installed new pumps just to still be having the same problems afterwards. When I ask them if they changed this fitting, it's always a no.