offical PSI #'s for Lift pumps from cummin

[C1B1DIESEL]

Okay here is the numbers I got from cummins for trouble shooting lift pump pressures. I seen the #s on the paper that cummins uses.

10 PSI min. at 3200 rpm no load

2 PSI min. @ full load

10 psi max return line restriction

6 inhg max fuel inlet restriction

5 PSI drop across the filter

 

[Steve Campbell]

The number that I do not understand is the "10 psi max return line restriction". Does that mean the return banjo "valve" is set at 10 psi or that the return line needs to be large enough to not cause restriction and build a pressure of 10 psi or larger?

 

[Ramafid]

I personally would want more than 2 psi at WOT but if that's what Cummins recommends I guess it's OK. Thanks for the info.

 

[Evan A. Beck]

Originally posted by Steve Campbell

The number that I do not understand is the "10 psi max return line restriction". Does that mean the return banjo "valve" is set at 10 psi...

Yes. Before I replace any overflow valve, (12V or 24V) I always remove it and check it with air pressure. 24V overflow valves usually start to open at around 10-11 psi.



Just a note about fuel pressure...



Its always good to check the overflow valve and fuel filter before replacing the pump. Replace as necessary. Filters and valves are cheaper than lift pumps!

 

[Lordsman]

???

Has anyone just taken their pump and moved it back 3 feet or closer to the tank as specified by pump manufacturer? Mine works good where it is(factory) and maybe it'll last 100,000K miles if its where it belongs.

 

[RADdodge]

C1B1DIESEL



Those are the same numbers DC published in the 2000 Service Manual, (pg. 14-70 - 71) as the max/min numbers depending :

5-7 psi minimum cranking

10 psi minimum idle

5 psi maximum differential across fuel filter

6 in/hg maximum vacuum in fuel supply (more or less the fuel filter but the test is the complete fuel system)



Also, the Overflow Valve Test (valve is located on the left side of the injection pump) specifies that the valve should open between 12 - 14 psi. (pg. 14-72) It is designed to open at approximately 14 psi. "Approximately 70% of supplied fuel is returned to the fuel tank. "

 

[Big Don]

Guys,



I know I am wearing this topic out, but I am concerned about lift pump pressure damaging the injection pump. My '00 has been upgrade considerably and at 3200 rpm's no load pressure drops to @ 4 psi. Not sure what it's doing under load, but I can't get my dealer to do anything about it. They checked it and say if it is putting out 10-12 psi at idel then they will not touch it. They do not understand why I expect it to maintain pressure at 3200 rpm's no load. I would really appreciate any documents that I can print and take to them to convince them otherwise.



thanks

Don







thanks

Don

 

[RADdodge]

I think it's been said several times before, if you have a positive reading at the injector pump inlet, then you are supplying more fuel than the pump is using. If it's 0 or forbid, suction, then the injection pump is pulling fuel and the lift pump needs attention.

(edit) I'm talking about anytime, particularly WOT.

 

[DiTrani]

Is there any word on whether moving the pump back by the tank will cause warrantee problems? I can imaging it would. I know lots of you don't care, but since I'm not into bombing and got the 7/100K drivetrain warrantee from DC (bought 12/01), I'm reluctant to move the pump. If the pump dies and eats the VP44, then it's DC's problem, but if I move the pump and the VP44 dies anyway, might be my problem.



I'm thinking about just replacing it once a year or so since it's pretty cheap, as regardless of whose problem it is, I don't wanna get stranded.



CD

 

[C1B1DIESEL]

been away, sorry for the delay,

steve the 10 PSI max return reading is after the check valve.

it is usually check at the line going to the fuel tank, past the tee

at the back of the engine.

The tee has a line coming from the vp44 and a line coming from the back of the head. this then returns to the fuel tank.

Hope this helps.

 

[rubberneck]

Originally posted by cditrani

I'm thinking about just replacing it once a year or so since it's pretty cheap, as regardless of whose problem it is, I don't wanna get stranded.



CD

It is all going to depend on how smart/cool your DC tech is. If he knows anything, he will realize that relocating the lift pump is doing nothing more than increasing its lifespan (all electric pumps like to push not pull) However, i understand your concerns as not all dealer techs will see this and may be more interested in sticking you with the bill rather than helping you out.



Rather than replacing the pump yearly, why not put in a fuel pressure gauge?? Not only will it save you some money, it will add piece of mind. Note my first lift pump did not make it a full year. (only 14k miles and 9 months). Fuel press guage is where its at IMHO



Big Don, rather than suffer the aggravation of trying to educate the DC tech on fuel pressures, why dont you revamp the fuel system. Put the pump or a new pump at the rear, and get rid of those stock banjos?? might be easier and save you a few grey hairs. If they do not understand how you could be concerned with low pressures, sounds like they might not be the ideal folks to be working on your truck anyway. just my . 02

 

[Diesel Freak]

I am definately in the green on this one.



12. 5 at idle

7. 5 WFO

 

[777 MECHANIC]

PRE OR POST FILTER PRESSURES

Are all these pressures you guys are reading pre or post filter?

 

[Steve Campbell]

Typically post

Some have a dual set up, I think most are post filter for two reasons. 1--to know how much pressure is at the VP44. 2--to know when it is time to check/change the fuel filter (pressure reading lower than normal for your truck).

 

[rubberneck]

Re: PRE OR POST FILTER PRESSURES

Originally posted by 777 MECHANIC

Are all these pressures you guys are reading pre or post filter?

Post, i could honestly care less what is before the filter, i want to know what i am seeing at the vp44

 

[dresslered]

I've been watching my numbers over the last 10,000-miles and have noticed a steady decrease. I would say, that a better indicator is to compare your readings to what they were a few months ago (regardless of the actuals). Once the pump starts to go, it's over with and just a question of when.



P. S. Make sure that you don't have a dirty fuel filter though.

 

[roadranger]

Re: PRE OR POST FILTER PRESSURES

Originally posted by rubberneck

post,i could honestly care less what is before the filter, i want to know what i am seeing at the vp44

I run mine PRE, as the whole reason for the gauge is to see what that POS lift pump is doing. When the gauge shows below minimums, you KNOW the pump is crapping out- no guessing if it might be the filter.



I change the fuel filter with the oil filter anyway.

 

[dresslered]

Well, actually roadranger, you could have a single tank of bad diesel give you good pressures pre- while having no pressure post-. Post pressure checks the lift pump as well as the filter condition.

 

[pwr2tow]

have the best of both worlds, put in two sending units one pre and one post with a on off on switch between. Works for me.



Ron

 

[777 MECHANIC]

PRESSURES

I just got my duel senders set up today. Im running 12psi pre and post at idle. The idle seems a little low to me.

At WOT I'm at about 5-6psi pre and post. Im not seeing much differential between the two. I guess because I just changed my filter. How do these numbers sound?

I've got the banjo fittings. Just have to install them.

Hopefully I will get a little higher pressures.