It does make one wonder about 15 years of experience on a system that hasn't existed for 15 years.

Edward

 

my point is/was that he could have a hundred years experience and still be a lousy mechanic....and the second point was that you can have 10psi of pressure and not have enough volume...

 

Ok, I'm not sure if this will help anyone's thinking but here goes.I know you are talking about fuel pumps but I think the principle is the same.Years ago in big trucks they would run about 60 psi oil pressure to force oil to the bearings. Then they got the idea that they would lower the pressure to around 30 psi BUT the volume would be increased thereby increasing the amout of lubricant to the bearings. They have since reached a happy medium and run around 40psi at normal operating speed trying to get the best of both worlds.

 

Wether you are talking about fuel, oil, water, or any other 'liquid pump/transfer' system, it all falls under the priciples of 'Hydraulics'. Hydraulic systems have been around for quite a few years. Even in the Firedepartment, it is vital to have the understandings of 'hydraulics', to ensure things are done efficeintly.

 

Is this lift pump problem in a mechanical B engine or the ISB engine , there are two different procedure for each one. I will give you the latest procedure for the ISB , most likely you have a F.C. 368 in the ECM . if the mechanical pump , you should check your outflow valve before you go replacing your lift pump, and disassemble the outflow valve and check spring and the ball seat,

 

firestorm
You are correct that hydraulic theory has existed for many years but the topic being addressed in this thread is the Carter electric lift/transfer pump on a Cummins engine.
This configuration has not existed for 15 years, which raises the question of, how can one get 15 years of experience diagnosing electric Carter lift/transfer pumps on a Cummins if that configuration hasn’t been around that length of time?

Edward

 

Welp, just to help me better get the idea, would someone explain to me(type slow so I understand) how you can keep the 10psi on a given size pipe and change the volume. No fair kinking the pipe/hose now. No restrictions.

 

You might consider one thing though. Sitting in the shop and running it up to 2000 a small volume may produce the pressure, but going down the road even just pulling the truck would take more fuel volume to produce the same pressure. In other words, driving the truck in direct or od at 2000 may not produce the pressure because there is not enough volume. This may be why they went to volume instead of pressure, in the shop the pressure would not be accurate. You also could not get a wot pressure reading in the shop. He may not be so far off.

Dojman, same pump, same line, the injector pump restricts it until there is a load that requires more fuel, the restriction decreases, the volume increases, the pressure drops.

 

Cummins has been doing the Volume verses Pressure test. If you guys have a Cummins ISB manual laying around you will see the test procedures are for volume not pressure. Dodge is now adopting a Cummins procedure. It's been discussed before that you should be more concerned with volume for you VP than to be strickly going by PSI.

 

If you maintain the pressure at high volume, you have the necessary volume.

 

I think they went to volume testing in the shop because they can't properly load the engine except on a dyno- customer acceptance of dealership mechanics doing WOT runs through all gears could be a little limited too

AlpineRAM

 

The best solution is to install a FP guage AND then do a fuel filter change and volume test before replacing the lift pump.

The FP is nice because it does give some indication of fuel filter health.

 

Ok, I think I'm there with you now. I wasnt taking into account the resistance or draw of the inj. pump(idle or working) I was just looking at the output of the LP alone.

 

I recently installed mechanical FP gauge in pre filter port. LP only put out 9 psi at idle. So I took it to Dodge dealer, but they said it passed the flow test. So, since I could not see what psi was at WOT , I installed electric FP gauge in post filter port. Still have 9 psi at idle, but at WOT (just the truck, no load) fp falls to 3 psi. I bought the truck used w/83k miles, now have 95k on it. Should I just forget what the dealer says and buy a new LP . Truck runs great, pulls my boat like it's not even there, have not pulled a real heavy load yet.

Oh it's a 99 QC longbed w/nv5600 tranny.

 

Not necessarily. Pressure is the measure of restriction and not volume. If you put your finger over the end of the hose you create pressure and lower the volume and releasing your finger lowers pressure and increases volume. If you notice that your psi's slowly degrade over time and you've eliminated possible causes then you should be concerned with the pump giving out. But as long as you have 1 psi at WOT then you know that your pump is still producing more volume than the VP can use. Remember that the fuel return is about 70-90 percent of the fuel delivered to the VP depending on setup.

If you have 15 psi at idle and 0 psi at WOT what is your return line volume? Is your lift pump bad? If you have 15 psi at WOT is your lift pump good or do you have a restriction?

You can spend $600 on a FASS or replace your lift pump about 5 times. Is 30 minutes of labor worth $600? I still have my original pump at 33,000. Is this newest pump from Cummins a better one? They seem to think so. The older ones were horrible but the failure rates from Cummins on the latest released pump are down substantially.

Bill K did a big write up on this in the TDR and did it with a flow meter on the return line. Read this and see how people measure PSI and confuse this with a good or bad lift pump verses what the actual volume of the pump output is.

With this said if you used to get 15 psi at idle and now 6 months later you are seeing 8 psi at idle and you've eliminated possible causes, then replace the pump. But this is what the pressure gauge was really meant to do, was to monitor the normal pressures and not the extremes and to warn of a possible problem.

My .02..