Cummins Diesel Forum banner
Cancel

Fuel pressure question

2445 Views 25 Replies 12 Participants Last post by  Mopar1973Man, 
R
OK, I know 5psi is low (01 Cummins) and I'm staying above that at all times, but I wanted to take a poll. My truck has a cold idle pressure of about 12psi. Hot idle 14-15psi. Cruising on the highway at about 70mph / 2000 rpm...it runs about 10psi. Decel on the highway, 12psi. If I crack into it to merge or tow, it drops to about 7psi. The 25 second free pump cycle netted a hair over 10 psi earlier tonight. Maybe 12. I was using the cycle more to locate the pump in the truck (wasn't sure if it had the in-tank update or not) than to check pressure.

I've had the gauge installed for about a year now, no real change in the numbers. They're starting to seem lower this time of year because the weather is colder but I keep a log in the console and they're actually pretty much unchanged.

I also have one of the 5psi warning lights - it never even flickers so I know I'm not touching 5psi.

221k miles. Original pump as far as I know, mounted right on the side of the block like it should be. Stock truck with a BHAF, boost, EGT, and fuel pressure gauges. 6 speed 4x4.

Taking a poll - should I pick up a replacement pump and just have it handy (and if so, what's recommended for a stock-but-used-for-towing truck)? Wait till the numbers actually start to drop? Or just drive it and keep an eye on it, and see if the pressure ever drops?
Reply
Save
Like
1 - 20 of 26 Posts
01CumminsPower01
Get a FASS 95
Reply
Save
Like
Mopar1973Man
14-20 PSI is optimal.

10-14 is marginal and might start causing damage.

Below 10 PSI you doing damage.

More or less like saying the minimum oil pressure for our engine is 10 PSI at idle and 30 PSI at 2K RPM's. How long would you expect the engine to last at bare minimums. Even worse how long do you expect it to last below rate? Same hold true for the VP44 the fuel pressure is a means of cooling the electronics and lubricating the pump. So being below 14 PSI you risking your VP44 period.
Reply
Save
Like
zack_76401
Can anyone provide published data on PSI numbers? A VERY well known diesel company told me anything over ten is great-no worries. I was also told too high would kill the pump. My pump is at 290k so I must be ok.


Sent from AutoGuide.com Free App
Reply
Save
Like
jmd025
zack_76401 said:
Can anyone provide published data on PSI numbers? A VERY well known diesel company told me anything over ten is great-no worries. I was also told too high would kill the pump. My pump is at 290k so I must be ok.


Sent from AutoGuide.com Free App
Click to expand...
My 250k factory pump has been eating this for quite a while with no issues....

http://youtu.be/VcjKtup4VCU


Sent from AutoGuide.com Free App
Reply
Save
Like
me78569
E
zack_76401 said:
Can anyone provide published data on PSI numbers? A VERY well known diesel company told me anything over ten is great-no worries. I was also told too high would kill the pump. My pump is at 290k so I must be ok.


Sent from AutoGuide.com Free App
Click to expand...
The over flow valve opens at 14psi. Not sure what else you need to know when it come to the health of the vp44 since it is cooled by fuel.

Above 14psi no matter what is wgat you aim for.

Sent from AutoGuide.com Free App
Reply
Save
Like
zack_76401
So it would seem anything over 14 is a waste. I stay 16-14.


Sent from AutoGuide.com Free App
Reply
Save
Like
Y
Over 14 PSI, it goes through the overflow valve to cool the electronics. The more pressure, the more volume to cool. Optimal is 20 PSI idle & 2-3 PSI drop at WOT.
You are extremely lucky to have a VP44 last that long with the stock pump. Check out the school bus forums, those were going out at 60K....

Ed
Reply
Save
Like
Mopar1973Man
Right out of the Dodge FSM...

Approximately 70% of supplied fuel is returned to the fuel tank. The valve opens at approximately 97 kPa (14 psi).
Click to expand...
Enough said.

Now as for the 70% return you need a lift pump and plumbing system to supply at least 90 GPH. To meet the 70% rule under WOT operation. Anyone with a live data tool can measure the flow to the injectors (30%).
Reply
Save
Like
D
How often you change your fuel filter? Mine did the same thing swapped out the filter and I was tuned in
Reply
Save
Like
Mopar1973Man
DriftDodger240 said:
How often you change your fuel filter? Mine did the same thing swapped out the filter and I was tuned in
Click to expand...
Every 30k... But now going to 50k.
See less See more
Reply
Save
Like
zack_76401
I have a FASS 150 feeding my stock VP.


Sent from AutoGuide.com Free App
Reply
Save
Like
zack_76401
Mopar1973Man said:
Right out of the Dodge FSM...



Enough said.

Now as for the 70% return you need a lift pump and plumbing system to supply at least 90 GPH. To meet the 70% rule under WOT operation. Anyone with a live data tool can measure the flow to the injectors (30%).
Click to expand...
So at 14 psi my fuel is going back to the tank... How is that cooling my VP? Nowhere in the FSM does it point blank say what pressures we should have.....


Sent from AutoGuide.com Free App
Reply
Save
Like
  • Like
Reactions: 1
jmd025
Mopar1973Man said:
Right out of the Dodge FSM...



Enough said.

Now as for the 70% return you need a lift pump and plumbing system to supply at least 90 GPH. To meet the 70% rule under WOT operation. Anyone with a live data tool can measure the flow to the injectors (30%).
Click to expand...
For a near stock truck like yours....pretty legitimate guesstimation.



When you are using 300-400% more fueling demand than stock hp levels require, things change
Reply
Save
Like
Mopar1973Man
3
zack_76401 said:
So at 14 psi my fuel is going back to the tank... How is that cooling my VP? Nowhere in the FSM does it point blank say what pressures we should have.....


Sent from AutoGuide.com Free App
Click to expand...
Here is the minimum by the FSM. But its flawed...


I tend to look at the Bosch's spec more with the overflow valve and keep the fuel flowing under the electronics and keeping them cooler. But hey if you like throwing money away and burning up VP44's that your choice, your truck and your money... But please don't come back here and yell about how crappy the VP44 pump are. They work just fine if taken care of properly!

Take notice to the divided chambers and the direct fuel contact to the bottom of the PSG circuit board. So when the overflow valve is open >14 PSI then the fuel is rapidly trading heat away from the mechanical parts and the PSG electronics of the VP44. The backside of the PSG is also aluminum so perfect heat sink to fuel!


See less See more
Reply
Save
Like
me78569
It's pretty simple, the vp44 is cooled by fuel. If the overflow is open you are able to send that hot fuel back to the tank and replace it with cool fuel from the tank. No different than a thermostat on a truck opening causing coolant to pass through the radiator. So to prevent heat from building up in the VP you need excess fuel flow through the pump and back to the pump. This requires 14 psi.
Reply
Save
Like
  • Like
Reactions: 1
Y
You can lead a horse to water...

Ed
Reply
Save
Like
jmd025
You can also lead hundreds to "Drink the Koolaid"

:thumbsup:
Reply
Save
Like
  • Like
Reactions: 1
zack_76401
Mopar1973Man said:
Here is the minimum by the FSM. But its flawed...


I tend to look at the Bosch's spec more with the overflow valve and keep the fuel flowing under the electronics and keeping them cooler. But hey if you like throwing money away and burning up VP44's that your choice, your truck and your money... But please don't come back here and yell about how crappy the VP44 pump are. They work just fine if taken care of properly!

Take notice to the divided chambers and the direct fuel contact to the bottom of the PSG circuit board. So when the overflow valve is open >14 PSI then the fuel is rapidly trading heat away from the mechanical parts and the PSG electronics of the VP44. The backside of the PSG is also aluminum so perfect heat sink to fuel!


Click to expand...
I never burnt up a pump. I run a FASS 150 and always have 14-17 psi . I'm not sure where your going.....I have 290k on this vp. About 280 on stock lift pump before I got a FASS. This crap is overrated and blown way outta proportion. It does happen.




Sent from AutoGuide.com Free App
Reply
Save
Like
R
I'm going to swap my filter just to be safe.

Thoughts on the FASS DRP versus a frame-mount system? FASS DRP with a frame relocation kit? Or should I just bite the bullet and go with the "bigger" FASS frame mount system?

Stock motor. Stock injectors. BHAF. *maybe* getting an exhaust at some point, to help lower EGTs when towing. No plans for big injectors or anything - this is ol' reliable. If I want to go fast, I have 150hp+ motorcycles. I want the truck to be reliable, work hard, and survive.
Reply
Save
Like
1 - 20 of 26 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Cummins Diesel Forum
A forum community dedicated to all things Cummins Diesel! Originally founded for owners and enthusiasts of Cummins powered Dodge pickups, the Cummins Forum has expanded to include ALL Cummins Engine applications! Come join the discussion about reviews, drivetrain swaps, turbos, modifications, classifieds, builds, troubleshooting, maintenance, and more!
Full Forum Listing
Explore Our Forums
03-07 Performance Parts Discussion 03-07 Powertrain 2013-2018 General Discussion 98.5-02 Powertrain 98.5-02 Performance Parts Discussion
Top