low fuel press @WOT

[jkern]

well, yesterday i installed a pressure sender connected to a LED to warn me when fuel pressure dips below 5psi. well, guess what, at more than half throttle and greater than 1800 RPM, my little red LED shines brightly. my truck has only 25k miles on it, so do i take it to the dealer for a warrenty fix, or just put on the aftermarket performance lift pump?? and if the aftermarket one is the answer, is the mallory still the one everyone os recommending??

 

[DHatfield]

You would probably be best keeping it out of the dealers hands unless you trust your dealer. Is seems several people are using the aftermarker pumps mostly Mallory.



Does anyone know what the lowest pressure at WOT should be before the lift pump needs to be replaced. I just recently fuel pressure gauge in my truck and I get the following numbers: idle = 12 PSI, cruising (55-70 MPH) = 11 - 12 PSI, WOT = 8 PSI? For those of you with fuel pressure gauges what are your readings? I figured I would wait until WOT is at or around 4 PSI to replace the lift pump is this the correct assumption?

 

[rotohead]

With SW electric fuel press set up I have the same readings as DHatfield. 50K on original lift pump (w/replacement pump waiting in the wings).

Chuck

 

[Vaman]

Fuel pressure readings

My numbers are pretty close to yours... about 14 at idle, 12 running down the road, and down to about 8-9 at WOT. These numbers are post filter with a new lift pump and new filter. The service manual states a minimum of 10 psig at idle (pre filter) with a maximum of a 5 psi drop across the filter.

 

[jjdiesel]

Just had mine changed out because of weak readings. After filter:

10psi @ idle... ... ... 4psi @ wot. After change:

17psi @ ide... ... ... . 12psi @ wot. Put the new one on that the dealer offered. The part # has been superceded twice... . looks like they are making some changes to the thing.

 

[pwr2tow]

My pressure readings before lift pump replacement.



9 PSI before filter at idle.

9 PSI after filter at idle.

6-8 PSI driveing down road at 1900 RPM's before filter.

6-8 PSI driveing down road at 1900 RPM's after filter.

0-1 PSI before filter at WOT.

0-1 PSI after filter at WOT.



After pump replacement.



14 PSI before filter at idle.

14 PSI after filter at idle.

13-14 PSI driveing down road at 1900 RPM's before filter.

13-14 PSI driveing down road at 1900 RPM's after filter.

13-14 PSI before filter at WOT and full pull load.

13-14 PSI after filter at WOT and full load pull.



I noticed a definate power increase after pump replacement.



If memory serves me well I think DC will not replace pump under warranty until PSI drops below 8 at idle.



If DC does replace your pump under warranty make sure the numbers end in AC. If DC does not replace your pump and you want to for peace of mind, buy one from cummins not DC.



DC price $395. 00

cummins price $135. 00



I have read on this board that it is o. k. for pump pressure to be as low as 2psi bewcause injector pump will suck fuel.



My theory is the releif valve in the injector pump pops off at 10-14 PSI. If you are running lower than that then you are starveing the injector pump for fuel since no fuel will flow back to tank and if no fuel is flowing back to tank then how can the fuel cool the injector pump and lubricate it.



enough for now,

Ron

 

[HVAC]

Your Under Control

Douglas Hatfield, If you can keep your wot pressure readings at 4 psi or above then I propose that you are doing fine. Be sure to continue to check your readings from time to time.



Many of us have spotted pressure readings dropping to 0 and below. That's panic time IMO

--------------------------------------------------

Nowel/Performance Diesel

 

[Bigsaint]

I have my Mallory set @ 12 psi's - idle, which equals about 7-8 psi's @ WOT (for right now). This topic has been beaten to death and I still don't know if anyone can say for sure what is a "safe" WOT psi reading. My own feelings are that any number that show's positive psi's is probably okay, though I would get concerned if I dropped below 3 psi's. If you read any of the old posts on lift pumps, you'll see that one thing that we did find out is that it's more about flow/volume than psi's. Granted, you want to have at least a resonable psi number @ idle, but I believe that there's nothing wrong when your WOT psi's drop down to 3-4, especially if you are using a high flow (140 GPH) aftermarket pump. Check out the link below for some interesting reading on lift pumps and psi's.



http://www.centuryperformance.com/fuel.asp



Scott W.

 

[jkern]

thanks for the replies guys. with the setup that i have, i don't know real numbers of what the pressure is dropping to, just that it is below 5 psi. i have placed the sensor post-filter, as this is the actual pressure that the injector pump sees.



i guess from what i have read that i am OK for now, but really need to watch it closely.

 

[C1B1DIESEL]

After changing mine. 18 idle, 14 crusing, 11 wot. [/COLOR]

 

[mongoose]

for those that mentioned getting the pump replaced underwarrenty, i have a question. Does this pump fall under the cummins 100,000 mile warranty, or is it strickly covered under the DC warranty?

 

[Ray Torresdal]

INJECTION PUMP

If your lift pump is replaced under warranty, I would make note of the mileage in case the injection pump failed prematurely, but after the standard warranty. I would think one could make a strong case that weak lift pump caused damage to the injection pump. Has anyone had any experience along these lines??? Ray

 

[TowPro]

What was the orginal application for the switch you used, and did it need any adaptors to fit the pressure test port?

Originally posted by jkern

well, yesterday i installed a pressure sender connected to a LED to warn me when fuel pressure dips below 5psi. well, guess what, at more than half throttle and greater than 1800 RPM, my little red LED shines brightly. my truck has only 25k miles on it, so do i take it to the dealer for a warrenty fix, or just put on the aftermarket performance lift pump?? and if the aftermarket one is the answer, is the mallory still the one everyone os recommending??

 

[pwr2tow]

mongoose,

The lift pump should be covered under the 100,000 mile warranty but if you get a for a dealer they may try to dick around with you.

Ron

 

[Ron Bissett]

return psi

Originally posted by ronsram1999

My pressure readings before lift pump replacement.



9 PSI before filter at idle.

9 PSI after filter at idle.

6-8 PSI driveing down road at 1900 RPM's before filter.

6-8 PSI driveing down road at 1900 RPM's after filter.

0-1 PSI before filter at WOT.

0-1 PSI after filter at WOT.



After pump replacement.



14 PSI before filter at idle.

14 PSI after filter at idle.

13-14 PSI driveing down road at 1900 RPM's before filter.

13-14 PSI driveing down road at 1900 RPM's after filter.

13-14 PSI before filter at WOT and full pull load.

13-14 PSI after filter at WOT and full load pull.



I noticed a definate power increase after pump replacement.



If memory serves me well I think DC will not replace pump under warranty until PSI drops below 8 at idle.



If DC does replace your pump under warranty make sure the numbers end in AC. If DC does not replace your pump and you want to for peace of mind, buy one from cummins not DC.



DC price $395. 00

cummins price $135. 00



I have read on this board that it is o. k. for pump pressure to be as low as 2psi bewcause injector pump will suck fuel.



My theory is the releif valve in the injector pump pops off at 10-14 PSI. If you are running lower than that then you are starveing the injector pump for fuel since no fuel will flow back to tank and if no fuel is flowing back to tank then how can the fuel cool the injector pump and lubricate it.



enough for now,

Ron

Releif pop off is 10 -14 psi from the work of the injector pump excess fuel returned to tank lift pump I don't think is making this pressure . what do you think. Good post thanks for the info on the DC mark up. Ron

 

[Evan A. Beck]

One note about the overflow valve...



Spec says it's supposed to start opening at 11-12 psi, and be fully open @ 13-14. So, if your lift pump only puts out 8 psi, does this mean NO fuel is flowing back to the tank? No, it does not. The VP44 is like two pumps in one: High-pressure for injection, and low pressure for lube & cooling. The lift pump merely supplies the VP44 with the fuel to do this. The VP44 will actually suck fuel if need be, and the pressure on the outlet side will be enough to open the overflow valve, thus lubing & cooling the pump.



Lift pump pressure IS important, but the VOLUME is just as important, if not more so. This is where the problem lies with the failing lift pumps. They just are not putting out the volume the VP44 needs for lubing & cooling. Low pressure can be a signal of low flow, which is why everyone is all excited about their fuel pressure.



So what's the solution?



Well, there are several good things to do...



First, you can try drilling out the banjo bolts, which we know are a huge restriction to fuel flow. Gains are noticable, in both fuel pressure readings, and boost pressure too. It's a simple modification to do, and cost nothing! Gotta love that!



The next thing you can do, is upgrade the fuel supply lines, and eliminate the banjo bolts. Many members on the Board have done it, and again, the gains are noticable. Cost is around $180 if you use braided stainless hose and aluminum Aeroquip fittings.



If you really want to go all-out, you can move the lift pump closer to the tank, or even buy an aftermarket lift pump. Several members on the Baord have been expeimenting with Mallory, Holley, and Carter fuel pumps, and the results have been great. Can be expensive, some pumps are over $200.



For more information on the fuel system discussions, do a search on "Pumps, Lines, and Whatnot. " You'll find a whole slue of information.

 

[Bigsaint]

Good post, Evan.



Scott W.

 

[KWIKKURT]

Here's what I did. I still have stock fittings and spent less than $200 for everything!



I hooked up a second Carter pump from Napa. I have a head light relay triggered by the primary lift pump power wire.

Then the power wire from the relay runs thru a Hobbs switch so the second pump kicks in only when the psi at the vp44 drops under 10psi.



I then added a fitting to the fuel tank down near the bottom. Ran 3/8" line to the new pump then feed it the schrader valve port of the fuel filter banjo.



So if one pump fails the other will save the vp44!



My pressure gauge does not bottom out under full throttle and my max boost went from 38psi to over 42psi !!!



Talk about Power!!



With the new 5" exhaust it screams!

 

[HEMI 71 GTX]

Ok 1st dumb question what is WOT? Second is what fuel pressure gauges are you guys using. I have been looking around for one, are you guys using anilog gauges and bringing a fuel line inside the cab? The only digital gauge(cyberdyne) I could find is 0-16 psi unless you go to their 0-150 but it costs $300 bucks. If you have a scotchlock on your injector pump wire are you bringing it to your dealer with it removed to get warranty work? Where is the best place in the fuel line to locate the sending unit?

 

[Tom W]

Fuel pressure

WOT is wide open throttle.

I used Stewart Warner gauge with electrical sending units. Cost for one gauge and two sending units was about $75. 00.

I had my pump replaced under warranty at 75K miles. Also replaced lines and banjo bolts with Aeroquip braided lines. Pressure now holds at 13 - 14lbs even at WOT - before it would drop to zero.

Tom



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