I would like to get to the bottom of this. The stock fuel pump on our CDT's seem to be pretty weak. We got some pretty smart fellas on DTR and I think we should put our heads togeather and figure it out. If we come to a conclusion we then could petition Carter, Dodge, and Cummins to instigate a fix and a more reliable LP.

I need a few old pumps to tear apart, I'll pay shipping.

If you want to tear an old one apart you'll need to grind or cut the bowl off of the manifold, and carefully examine every part. Pull the motor rotor and look in the bottom. I am really suspect of the circuit board at the bottom of the bowl. There are 6 resistor looking things that seem fragile to me. The vibration from the engine cannot be good for a circuit board.

Also, anyone with a weak pump, one that fluctates pressure try soldering the wires to the pump to avoid the connectors. Could the connectors be arking from the vibration?

These pumps are mounted directly to the engine. They seem prety delicate to be direct mounted to the vibrating motor. Seems to me a vibration isolator may be a better set up.

Just some ideas I have had about the LP. Any more?

 

I have an '02 and at 77K, my pump pressure is still like day 1. I often wonder if the high incidence of reported failures on the forum is because if the LP fails, the owner signs onto the forum to get an answer. But you don't hear from the ones that continue to run without issues.

 

I wonder if the Check ball failure could be remedied by inserting a few feet of coiled hose after the lift pump. I believe the success of the high flow hoses is attributed more to an accumulator effect rather than a flow improvement. If the check ball seat is being hammered because of pressure demand fluctuation, an "accumulator" would relieve it. I am going to try it and report pressure changes/improvements before and after. Only problem is it will be a few weeks before I am home to try it. Comments are welcome.

 

Can you explain the "check ball failure"? I saw the check ball when I took the pump apart, but I'm not sure what could fail.


Also, can someone (an expert) explain how the LP pump is supose to work? What is the theory behind the pump? When does it run and when does it shut off?

 

I believe the check ball keeps fuel in front of the LP and prevents it from draining back into the tank under certain circumstances. The LP runs as long as the engine is running and sends fuel to the IP. Excess fuel is used to cool the IP and is returned to the tank. When it's working right, that little bugger can pump some serious amounts of fuel. You should see how quickly it fills the filter cannister. I found out the hard way. BTW, If you looking for an expert....it ain't me!

 

As a correction to my previous post, it is the relief valve (ball) that I was referring to. The small volume between LP and Injector pump seems to hinder proper pressure regulation, and constantly hammer the ball, seat, and spring. The filter and housing holds a fairly large quantity of fuel, but is non-expansive, as an accumulator should be. That is why I believe a few feet of coiled fuel hose would help in more constant pressure demand at the LP. More "flexible" volume, more consistent pressure. Just a theory.

 

Interesting theory.

In taking my old one apart I am trying to figure out why there is a circuit board on the bottom of the pump. There are 6 resistor looking things I am looking into what they do. I believe it is vibration from the engine that is damaging the LPs.

I need a few old LP's to I can test my theory. I'll paid shipping.

 

When my pump failed I took it apart and found the bushing that holds
pump rotor to the motor shaft was wore out. Motor would run fine but
wouldnt spin the pump. I put it all back together and had it replaced
under warrenty.