Engine/Transmission (1998.5 - 2002) Fuel Pressure Advice

[ThomasHill]

I recently installed a fuel pressure gauge on my truck. The truck runs fine but I don't do much towing. The pressure numbers are:



12 PSI idle

6 PSI WOT



Should I be worried? I would rather do something about the lift pump before I need to replace the VP44.

 

[Oil Burner]

6 psi at wot is about as low as I would want to go. Don't let it get much worse than it is now. If it stays where is it as, then I might keep running it.



FYI, a new stock type lift pump should idle between 14 and 16 psi.

 

[DieselRam30]

I agree with the previous post. Six is the low side of acceptable, but considering your truck is stock, it's probably ok for now. Just monitor your pressure and see if it goes lower or there are other problems.

 

[bbodammer]

keep your eyes on it!! I get 14psi at idle and no lower than 10psi at wot. Even with the box on I only get down to 8psi. I recently installed a new lift pump so maybe that has something to do with it.

 

[Cummins360]

I installed the in the tank conversion on my 99' and my gauge reads about 6 or 7 idleing and 4 or 5 at WOT. But I read once on another TDR thread that its the volume not the pressure that you should be worried about, and that pump can suppily quite alot of fuel very fast (bad experiences).

 

[MMcfall]

Sorry for the long post below but..... I have been watching numorus threads regarding fuel pressure and LP and VP's and decided to ask Cummins directly. Below is their complete response and the design specs. Waiting on a response from Bosch.



Wed, 04 Jan 2006 12:47:24 -0500 (EST)

From: -- email address removed -- Add to Address Book Add Mobile Alert

Subject: Re: RQST00000402246





Summary: 65216 VP-44 Fuel Supply Pressure Requirement



Solution:



Thanks for your Email message.



You may need to add an additive if your fuel is in question. Lubricity and

water problems are the two big factors. For more information, contact Fleet-tech

Customer Assistance at 1-800-22FILTER(1-800-223-4583) fax 1-800-999-8664 or visit

us at www.fleetguard.com



When the transfer/lift pump fails fuel flow may or may not stop flowing to the

VP44 pump. It all has to do with the position the pump fails in. If you had a

gauge that could read positive or negative pressures on the outlet side of your

fuel filter you could see when there was a problem. At that point you could

stop and fix the problem with your truck. At that point the problem may be a

filter, plugged inlet line, transfer/lift pump or something simple.



Information about pressure:



Concerning lift pump pressures for ISB 24 valve engine, in the Ram application,

the following information is from the Cummins ISB Troubleshooting and Repair

manual, Bulletin number 3666193. This information applies to engines having the

Bosch VP-44 injection pump (not the high-pressure common rail found on 2003 or

later models).



The lift pump pressure is only one parameter pertaining to fuel system

operation/diagnostics, and as long as you have positive pressure to the VP-44 at

adequate flow, your engine should run fine. "Adequate" means normal performance,

starting and smoke levels. Any issues with the engine running outside of the

below listed pressures being in their respective proper ranges should be addressed.

The numbers in the manual are:



Idle speed:

700-1000 rpm

Maximum fuel inlet restriction to lift pump:

6 in Hg

Maximum Fuel Pressure at Fuel Filter Outlet (engine cranking): 4 - 8 psi

Minimum Fuel Pressure at Fuel Filter Inlet (engine running): 8 - 17

psi

Fuel Drain Line Maximum Restriction:

10 psi

Fuel Inlet Maximum Temperature:

165 deg. F

Engine Minimum Cranking Speed:

150 rpm



Excessive smoke can be a symptom of improper injection timing, which MAY be

caused by insufficient fuel to the VP-44. Variable pressure within the pump

rotates the cam ring that affects/effects injection timing changes; insufficient

fuel delivery to the pump will affect the pumps ability to establish the correct

timing per operational condition. Normally this is a blue-ish white smoke.

Black smoke is indicative of over-fueling (relative to the amount of air).



The fuel flow test (005-011) states to run the engine at high-idle (running on

governor with no load) speed; the outlet side of the filter should read 10 psi

minimum. To be thorough, one needs to check at high-idle as well as idle and

measure at the correct places. Under high-idle conditions the pressure drop

across the filter is to be 5 psi maximum.



The manual further states, not to operate the fuel system with suction

restriction of more than 3 psi but Bosch prefers that there is no negative pressure on

the VP-44. We are not aware of any durability validation tests at "outside of

acceptable operation" parameters or that negative pressure might cause VP-44

failures due to the lack of sufficient fuel for pump lubrication. Unlike the

P7100, the VP-44 is lubricated by the fuel which circulates through it. Bosch may

be able to advise the effects of low lift pump pressure on the VP-44 injection

pump.



The output of the fuel lift pump is checked via test (005-045-012) by measuring

the output pressure, using a pressure gauge at the fuel filter head tap. For

long injection pump life, the Bosch VP-44 pump requires clean No. 2 diesel fuel,

with no water or foreign debris. Owners should be very careful during fuel

filter maintenance or replacing the lift pump, to ensure that no debris gets into

the injection pump side of the filter.



Always use the lift pump to fill the filter. This can be done by bumping the

starter with the key switch but not starting the engine. The lift pump will run

for 25 seconds. Turn key off and repeat two more times then filter should be

full.



We thank you for your interest in Cummins products. Please let us know if you

need assistance in locating the nearest Cummins-authorized Dealer or Distributor

Service Provider. For assistance in locating a Service Provider, feel free to

use Cummins North America Dealer Locator, which can be found on Cummins website:



http://wsl.cummins.com/ServiceLocator/jsp/controller.jsp?action=servicelocator



Please let us know if you have other questions and if away from your computer

or have a time-critical request that needs more urgent attention, feel free to

call us toll-free (from North America) at 1-800-DIESELS (343-7357).



Email direct: -- email address removed --



Regards,

--

Powermaster

Customer Assistance Center

Cummins, Inc.

Columbus, Indiana, USA





Free QuickServe Online for Consumers http://quickserve.cummins.com

 

[fox]

I installed the in the tank conversion on my 99' and my gauge reads about 6 or 7 idleing and 4 or 5 at WOT. But I read once on another TDR thread that its the volume not the pressure that you should be worried about, and that pump can suppily quite alot of fuel very fast (bad experiences).

It is the volume that gets the pump lubed.



BUT, if nothing is changed to increase or decrease the volume, with only changing a pump and seeing less pressure means there is less volume.

Keep the pressure near or above 8-10 to help the pump survive.

The intank pump conversion looks like a failure.

Spend the money for a RASP or a FASS, or simply add a pusher pump.

A theory also, is that you only need to keep it at 12-14 under all conditions!!! Over that and the stock pump beats up its regulator and puts debris in the filter.