Agreeing with uncle bubba fully

 

Myself I live by the Dodge FSM book more so...



I tend to suggest 10-20 PSI range as a norm... Being most AirDog's and FASS pumps come out of the box at 17-18 PSI factory set. After 20 PSI most people complain about hard strarting issues. Like my AirDog 150 idles at 17.5 PSI and 15 PSI at WOT.

Most people that allow pressures to fall below 10 PSI will fail the TSB Volume test by Dodge. (TSB 14-002-03 Diesel Transfer Pump Diagnosis)


Here is how to test cranking pressure...

 

25psi will not hurt a thing. There are guys that have been running that much or more since BOMBing began. If you get hard starts, then you will need slightly lower pressure. There is much less to fear from high pressure than low pressure. Give me 25psi over 10psi any day.

Regarding the overflow valve, it's function is NOT to regulate internal case pressure for the VP44 but rather to prevent some fuel from draining back from the case. In other words, there is no direct connection of the overflow valve to inlet fuel pressure.

You can have 20 psi at the inlet of the pump without even running an overflow valve. It's just to slow the rate of the bypass fuel and keep the case full. In my estimation this is for cooling purposes rather than fuel pressure control.

And yes, I am still running 45psi at idle and 37psi at WOT.

Dave

 

And Dave how would you asses the benifits of running this much higher than normal fuel pressure. Of course we know air cant be removed from it at that pressure. Are there other benifits? I've seen multiple trucks come in with high fuel pressure hard starts and not soon after pump failure of 1 year old pumps. I'll be honest, I disagree. I know some folks run a higher pressure, but considering I took a SO-vp pretty much to the limits that have been set with the SO on 15 psi? I'm really not trying to be rude in anyway, just stating my opinion. I completely respect your opinion! Not to mention as said before, Bosch specs say no more than 15, We all understand your prespective on the O/F valve , that makes sense to me. I ran a higher pressure for a while with no evidence of any gain or increase. There's really little damage to be done to the pump with high pressure and I understand that but even if, whats the point of extra load on the pump?

 

Good point... I do think going that far is a bit to much... But Congrads to you for making it work at that pressure but I don't think I'll try it will mine...

 

There is absolutely no point of running high pressures as I do. The point is that many guys do run high pressures with no ill effects. I am not offended by the perception that lower pressures are better, but it's only someone's opinion.

Here's the deal. Bosch has never stated in any form of print what acceptable pressures, if any, are acceptable. I see the same Dodge FSM page reprinted over and over. And the truth about that is, why listen to Dodge when they couldn't get the fuel system right in the first place? I have heard rumors Bosch has a spec somewhere. I am hoping it can be produced. But after years of debate, still nothing.

With the number of cams I have installed running an unregulated 12Valve lift pump and a single failure to date, I am sold on the higher pressures NOT hurting the VP. I have guys that wanted a regulator and most of those chose to go to 25psi. Not saying it's right or wrong, but those are choices different individuals have made.

As far as additional wear, until the VP fails, I can't say that I have experienced any additional wear. It would stand to reason that more pressure equals more wear. I can't dispute that. But, with over 80K on this pump, I don't know how much wear I have added. I am sure it'll fail someday and when it does I will finally install the regulator I built years ago.

Regarding the advantage to higher pressures, for most there probably is not any. With this pump, I picked up 35HP with the higher pressure. So if it works or not for others, it works for me.

Again, I am far more worried about low pressures for anyone looking for a fuel pump solution. To me, keeping pressures at a minimum of 16psi at minimum seems to be the most consistent for power. While I am convinced higher pressures do not hurt anything, it is reasonable to assume that the added pressure can and will add wear to the lift pump and may introduce additional heat. Again, how much of each is debatable and results can be skewed to show either point.

The only reason I post about higher pressures is to make sure that guys don't get caught in the trap that there is only 1 right way to do things. True, some guys get hard starts with electric pumps at pressures above 20psi. This is far less common on rebuilt pumps BTW. And I try to post good, accurate info, not stories or hearsay about what will or will not work.

Dave

 

good write.

 

Very good! I agree, Alot of times customers get pushed into somthing they may not need to spend a fortune on. Not to mention theirs plenty of much more affordable systems. My concern with high pressures with his setup
1: his factory pump isnt designed to have a feed pressure over 5psi
2: IF a factory pump fails it's not a flow through design
3: Just like any of the holley blues, To maintain adequate flow, (maintaining 15psiWOT) it needs a 20psi at idle. I'm fine with 20 no problems but isnt that just working a pump thats not "designed" to have that kind of flow. While the pump is marketed for that flow is it really capable of providing it in this setup. I DO KNOW FOR A FACT that setup as a single pump that the Holley blue has a much shorter life than it would set at 7PSI for a Carb setup!

I'm really glad this post is going! It provides the folks on diesel bombers the ability to find this thread and get them some pretty technical and very needed information!

Again, Thanks for understanding my POV Dave!

 

The flow through one LP to another will destine both pump to fail here. they are doin nothin but fightin with each other. The slower pump is trying to internally bypass all the extra fuel that the stronger pump is tryin to pull or push through so both pumps are workin harder then they should. So in the end the slower pump will wear out it's bypass valve and the stronger one will wear out the motor.