How much f. pressure is too much?

[SNKEBIT]

I am seeing a constant 21-23 pounds, is that too much?

[mopartechnician]

I dont like going over 20. I set all pumps to 18 so there is still good pressure at w.o.t

I think they say 24 blows seals

Edited March 19, 2014 by mopartechnician

[Texas CTD]

I am seeing a constant 21-23 pounds, is that too much?

 

It depends on who you ask. Honestly, just to stay comfortable, I would keep it below 20 PSI. But the main thing is to not drop below 14 PSI.

 

I think they say 24 blows seals

 

 

There's no evidence to back that up.

[Mopar1973Man]

There is no proof of excessive pressure blows seals but why take the chance of it happening. You only need enough pressure to keep the overflow valve open. So the suggested pressure is 14-20 PSI.

 

Your not going to increase flow much more... Return is much much smaller...

[Deafautotech]

I keep my cummins at between 20 to 22 psi depend on weather as it do varies but I kept it above 14 psi during highway...

[joecool911]

Kind of difficult to keep fuel pressure consistent with spikes at lulls in voltage. I keep wondering in my mind if there should be a voltage regulator on the fuel pump circuit at say 11 volts so that when the grid heater comes on it wouldn't affect the fuel pressure.

[Ilikeoldfords]

If should only be affected for about the first 5 minutes of the engine running. My grids stop cycling about 5 minutes after I start the truck then the voltage (and fuel pressure) stay rock steady.

[MnTom]

If should only be affected for about the first 5 minutes of the engine running. My grids stop cycling about 5 minutes after I start the truck then the voltage (and fuel pressure) stay rock steady.

That or until you get to 20 mph.

[joecool911]

Would more pressure force more fuel to the return circuit? Trying in my mind to evaluate higher pressure over 20 PSI versus the amount of fuel that potentially could be returned to the tank resulting in better cooling for the VP. That is a really small hole on the return side. I suppose the reason for that is limiting the amount that could be returned keeps more fuel in the pump and keeps the pressure higher inside the pump.

[mopartechnician]

Yes more fuel pressure means more return. Just wanna stay in that 14-20 range. I like 18-19 because of when my intake heater kicks on, it only drags the pressure down to 14-15

[hex0rz]

Okay, heres a thought:

 

The lift pumps themselves have a return line at the block. If the restriction only allows so much to return, the excess is returned at the filter block. So to me, it does not seem like it would matter either way?

[Mopar1973Man]

Wow... I'm set for about 17-18 PSI and barely see 0.5 PSI drop with grid heaters. Even then I can disable the grid heaters by just unhooking the battery leads for them. April is coming soon and I'll just unhook the grid heaters. Grid heaters are not much of a issue for me on fuel pressure.

[mopartechnician]

I think my problem is my batteries are shot and im waiting to change them when I do the tappet covee

[hex0rz]

I see a pretty big pressure swing on mine when the grids cycle. Dunno why...

[Mopar1973Man]

Check voltage drop of your main cables to see where your at...

http://articles.mopar1973man.com/general-cummins/34-engine-system/136-voltage-drop-testing-of-wiring-and-feed-cables

[KATOOM]

Would more pressure force more fuel to the return circuit? Trying in my mind to evaluate higher pressure over 20 PSI versus the amount of fuel that potentially could be returned to the tank resulting in better cooling for the VP. That is a really small hole on the return side. I suppose the reason for that is limiting the amount that could be returned keeps more fuel in the pump and keeps the pressure higher inside the pump.

 

Basically the reason for a "minimum" amount of fuel pressure began was so that the fuel pressure from the lift pump was equal to or greater than the internal low pressure side of the VP.  This pressure equalization kept the VP's plastic diaphragm from vibrating from the hydrodynamic pulses sent down from the higher pressure rotor.  So as time went on it was also conjured up that if the VP's overflow valve was set to fully open at 14-16 psi then making sure the fuel pressure was at or more than this 14-16 psi assured enough flow to match that circuit and therefore the VP should remain happy(ier) with enough fuel supply to keep it lubricated AND cool.

 

The same goes for the reason of that small return hole.  Without fully understanding the complete function of the VP we can only speculate as to why the diameter size.  There are three pressure areas to the VP.  Low, middle, and high pressure.  We can’t seem to figure out what area the return flows from.....but we do know that it’s not directly connected to the inlet as one would presume because of the common picture of the inlet and outlet being side by side.  The fuel has to flow into and around the VP before it exits but we just don’t know how far it makes its way around in there before exiting the excess.

 

Yes more fuel pressure means more return. Just wanna stay in that 14-20 range. I like 18-19 because of when my intake heater kicks on, it only drags the pressure down to 14-15

 

Strangely I don’t think there is ANY data which can back this statement with regards to the return flow increasing with the increase in pressure.  There's been considerable talk about this along with many schematic diagrams and dissection photos of the VP internals passed around, but until someone actually performs some tests and/or someone from Bosch steps up and releases the iconic VP data sheet, we won’t know.  But that doesn’t mean we're not still staying with the concept that fuel pressure needs to remain at no less than 14-16 psi all the time.  And we can say that too because we can all attest to what too low of fuel pressure does.

 

Okay, heres a thought:

 

The lift pumps themselves have a return line at the block. If the restriction only allows so much to return, the excess is returned at the filter block. So to me, it does not seem like it would matter either way?

 

A few of you are asking questions which seemingly CANT be answered.....but yet also seem to float around every few years or so.  As pointed out, there is NO acknowledged fuel pressure too high for the VP.  That doesn’t mean anything either other than we simply dont know because there is no recognized data.  Is anything over 20 too high or is it 25 or 30?.....again we DONT know.  But in saying that, there is tons of speculation and opinion to fill the informational void.  Its just understood that there's no apparent reason to try and cram more fuel pressure through the system than it needs and more so, is all that cramming doing good or is it creating hydraulic heat in the VP or in the fuel pump?

 

All this VP fuel pressure talk must slow down some day since not only has it been hashed out for years but some day most of us are going to move on to newer trucks and then migrate over to the newer model sections of the forum.

 

Hope I didnt make this more convoluted than it already was.....

[snowshoveler]

I have the DDRp pump on my 99.

After a few emails back and forth with the folks that sold it to me...I did a little spring modification.

20 psi at idle and 12 to 14 when leaning on the pedal a bit.

I installed a fuel pressure guage from my Cat on the top of the fuel filter and it always agreed with the Edge display.

A  month or so ago I noticed that my fuel pressure was dropping a bit and would go to 10 if I pushed it a bit.

I thought it was time for a spring switch...maybe they loose a bit over time.

I am a small engine mechanic so springs this size are no problem.

I installed a new spring and fuel pressure returned to the original good numbers.

Fast foreward to last week and I changed out the fuel filter...yikes it was yellow and slimy looking.

Fuel pressure is now 26-28 at idle and does not go below 20-22 when I push the go pedal.

Lesson learned...always check the simple stuff before assuming that things have gone bad.

Now to switch back to the original spring.

Ps the filter had about 5 K on it.

  Regards Chris

[Me78569]

I can add a little fuel to the fire.  During one of my trips my Pureflow pump decided it wanted to start pumping 35psi instead of 20psi, due to it being 0*f out and windy I just kept going, no blown seal in my vp44.  This has happened 3 or 4 times now and I have yet to have a seal blow. 

 

 

Now saying that ~400 miles total at 35 psi = vp44 safe at 35 psi isn;t true, but as stated above we really don't know.  I have been running my pump at 23-25psi idle for 15,000 miles now and no issues with the seal. 

[Mopar1973Man]

I've seen several run as high as 40 PSI but no one ever keep it there for very long nor was willing to report how it was doing. Maybe because it blew the seal? Damaged the Vp44 pump? Onee guy was proud of his mechanical 12V fuel pump at about 35-40 PSI but he disappeared.

[Me78569]

that's what I promote above 14psi no matter what, set your idle pressure at whatever it takes to keep your wot pressure above 14 psi.  If you idle pressure starts getting above ~22 psi to accomplish that then you have an issue with your pump.