MK4288

okay well i just got back from the dealer to get my lift pump replaced because its reading 9 psi @ idle and 7 psi cruising and about 4 when i really get on it. well i took it in and they checked it out and told me that the lift pump was fine because they tested its flow and it pumped out 60 of what ever increments (tablespoons probibly) and they won't replace the pump unless its under 45. well i then proceeded to tell them your guys recommendations and they told me that "fuel pressure is not a good way to monitor the fuel system because you can have 10psi but 10 what ever for flow or you could have 100 for flow at 10psi and not be able to tell." he then told me that the flow test is really the only real way to test the system in a diesel. now i am real suspect about this because i really don;t want to get in a cat fight with these guys what should i do? just let it go until my vp burns up and let them replace that. (still got 40k of warrenty) or should i shell out the cash and replace it my self? any type of opinion would help thanks.

MK4288

the only thing thats really bothering me is my pressure readings and they check out real low

Smkndzl

Cummins has changed the procedure for checking lift pumps , now they flow test the pump , one bump of the starter and leave the key on will run the lift pump for a 25 second cycle and the min flow of the lift pump output from the outlet of the fuel filter is 44 oz. of fuel , most of the one's I have checked have way more than 44 oz. of fuel. if it is close to 44 oz. I reccommed pump replacement.

phox_mulder

I'd say let the warranty take care of it while it can.

Once the warranty is up, go ahead and get the FASS, or whatever else comes up between now and then.

Even though the original warranty is included,
you still paid for it with a portion of that $30,000 you paid for the truck.

No use throwing your own money away buying lift pump after lift pump.
Let Mr. Daimler and Mr. Chrysler foot the bill for bad design.


phox

MK4288

well the dealer told me i had 60 onces during the flow test. so i take it its good. but the gauge reads as above. so is that gauge more or less for looks now then if that isn;t an accurate way to monitor the system?
as for the bill i think you got the right idea there PHOX i think i'll let the boys pay for it.

Rattletrap1

Flow is a better measure, but impractical to monitor while driving. I'd say the gauge still has a function to alert you of any changes to a given baseline.

You have to decide how comfortable you are with the test results (pressure vs. volume). Some of the places I go I would be a long way from help, so I don't go out with any real or perceived weak links. That said, I'd probably replace it if you used to have more TDR textbook pressures or obtain a spare.

AlpineRAM

I'd say that you can pressure-test your gauge. (Maybe it's off a bit- use a regulated shop air supply and don't exceed the rating of hte gauge)The flow test shows that there is enough volume there. If you reduce the restriction by consuming more fuel per minute you'll see a drop of pressure. But if your blowoff valve in the VP44 (mounted in the return line fitting) is shot you will also have low pressure with a good lift pump.

Just my 2c

AlpineRAM

TurboPirate24v

In my opinion...and I speak from practice...

Replace the Lift Pump yourself...and prevent slowly killing your VP44...which might just live until 100,001 miles and then your out big bucks.

It's $200 worth of Insurance....to prevent a $2000 disaster.

MK4288

well at 99,999 i plan on installing the fass system. i think testing the gauge is a good idea but i have no place with shop air i would take it to work and do it but the navy really looks down on that kind of thing.how would i check that blow off valve in the fuel system

renegade681

I agree with AlpineRam that Pressure=restriction. With that said just because your volume is at 60 fluid oz and your pressure is down doesn't mean your VP-44 isn't getting enough fuel. But my way of thinking is I'd rather have pressure around 10 to 14 psi and know my fuel flow is more than enough. I talked to a Cummins rep and he told me "DONT let it drop below 8 psi".
I personally think that the dealers are tired of replacing LP's and they are just gambling that they will last till 100,000 then its YOUR problem and not theirs . I'm on LP #2 at 26,000 miles and I have a FASS in the mail from Rip. I'm tired of putting bandaids on the truck and crossing my fingers.

Correct me if I'm wrong guys.

Matt

MK4288

see thats what i was told too. don't ever let y9our psi drop below 8 psi ever or else your vp-44 is in danger. but i don't really feel like footing the bill if it is supose to be covered by dodge you know what i mean. so i guess i will check the valve on the fuel system but i have to find out how.

Rattletrap1

Well...You could put a 5 gallon can on the hood with a 1/2" line feeding the VP. You'd have plenty of fuel, yet pressure to the VP would be nil. I can't see the VP suffering from that. My understanding is the VP doesn't need a "head of column", just ample supply.

bentwings

After reading every post on the lift pump problem it would seem to me that if you hooked up and inexpensive adjustable regulator (Holley)and set it at say 8 psi as noted above and tested the flow at 8 psi and you get say 40 oz.. you would have yard stick. If your flow dropped to some knowledgable number say 20 oz then the pump is going bad.

My old lift pump will pump like crazy with no pressure or just a free line. But put a restriction of a smaller line (increase pressure)and the flow drops to almost nothing. This pump has a huge wear gouge in the vanes from the check ball wallowing out the wall inside. It will pass the no load flow but not a pressurevolumn test.

Just my opinion.

bentwings

AlpineRAM

The VP44 will need a bit of input pressure in the CTD application. Otherwise the pump can cavitate internally. (small vacuum bubbles in the fuel)
An easy way to test the gauge for true readings is ask your friendly A/C tech if he would lend you a gauge and hook it up. If there's a massive difference chances are good one of them is

The overflow valve should open at or around 15psi. So after verifying the gauge you can hook up another pressure source and see whether the valve opens earlier than that or not- it should go to 15psi without letting stuff go through and then open. (transparent hose comes to my mind)

Just my 2c

AlpineRAM