My buddy has a 99' 3500 like mine, he's done some mild bombs with my help (275's, EZ).
As far as his fuel delivery system, he's on his 3rd lift pump. His truck has 103k on it, stock pump lasted to maybe 60-70k, we then replaced it with a Carter 4601HP. It lasted about 2 years, replaced it once again about a month ago again with a 4601HP.
Yesterday he calls me, tells me his truck is dieing (barely keep running) and has lost all fuel pressure. He pulled over and checked the lift pump, it was not running and was super hot to the touch. He then rapped gently (he says ) with a hammer, the pump starts to run again and the truck will now drive but still no fuel pressure. Seems that the pump impeller connection has sheered or is not engadging enough to generate any real pressure but it is now allowing the fuel to pass by the impeller (being pulled by the VP44).
Second problem...
The LP will not stop running! With the engine stopped and key out of the ignition the pump continues to run. He's got to pull the 20A engine controller fuse to get it to stop.
I pulled the lift pump to look at it and found that the impeller was damaged and not engaging the shaft properly. I also looked into the electrical issue and found that the 12v lead is hot all the time. It seems to be coming from the Cummins engine controller, if you unplug the harness from the controller the 12v goes away.
To me it sounds like something inside the controller has fried, or there is some TTL curcuit that has a sticky bit. I'm just glad it's not my truck .

Anyone heard of such a phenomina?

 

I'm not sure how this truck is wired , is the controler sepperate from the computor? which normanly controls function with grounds so if the controler is seperate the the controler acts like a relay and the computor closes ground on demand , hope this helps with diagnostics.

 

did you swap relays yet? if it was going to dead short perhaps it welded the relay cotacts closed....never seen it or heard of it but it would match your symptom

 

I just did some checking on the electrical system diagrams (I have an Alldata system on my garage computer).
It seems that the fuel transfer pump is triggered by the ECM (cummins computer), pins 15 and 35 combined. Fuel pump is directly gounded to some battery ground source. Output is pulse width modulated at either 100% during engine run or 25% at engine crank.
So there is no real "relay" that powers the lift pump. It looks like my buddy's going to have to spring for a new ECM.

 

In that case, why not a Catcher? Cheaper than Factory purchase, much more enjoyment. Search the threads.

 

If it was my truck there would be no doubt , I mentioned it to my buddy and he was like . Anyway he doesn't seem to have the time to wait for a Catcher.
I'll let everyone know how it all works out.

 

****UPDATE****

OK, my buddy brought his truck to a local diesel shop to have it checked out. The ECM had a few codes stored for over boost and one that was fuel pump related (not sure which codes exactly).
They charged him $90 to look at it and in the end told him that it would take further diagnosis but it "may" be the ECM.

So yesterday I had him come over and I removed his ECM and installed it in my own truck, the problem carried over with it. I then took a leap of faith (making him agree to buy me CaTCHER if anything went wrong) and intalled my ECM into his truck. Problem solved
I then swapped them back. So it was what I thought it was from the start, he's on the list for a MAD ecm and until it comes in he has rigged a switch in the cab to shut off the lift pump so that he doesn't have to keep pulling the ecm fuse.

 

Haulin,

I beg to differ with you on where the lift pump gets it's power. The lift pump is grounded directly to the chassis,power comes from pins 15 and 35 on the ECM (cummins computer). My electrical schematics are very clear on this point.

Pusher pump wiring is not the issue here, the truck in question doesn't have a secondary pump. We have thoughly check all the other curcuits and narrowed it down to the ECM, which was then proven when I changed it out.

Thank's for you attempt at helping though!

 

I am using an AllData technical service system which contains factory Dodge service schematics as well as all TSB's and related info.
It is what 99% of the repair shops in the nation use for their technical reference.

 

Ok I never try to give wrong information, and in this case you are right as 8W-30-31 of the service manual for the 1999 shows exactly what you related. You have my apologies.

Obviously there are some differences along the way. I was haveing low fuel pressure and intermittant problems and a diesel shop ran a photostat of the schematic that I discribed. It worked for me and I was sure that it was accurate.

I spent some time tracing the circuit on mine and a voltmeter showed floating ground on the negative lead to the lift pump. I cured my problems by grounding to the chassis. This went along with the schematic that I had received. I then received full 12 volts to the pump. At a later date I lost the 12 volt feed the same as BigBlue did and went to the other method of feeding it fromt the ASD relay. It has worked fine there for 100k or so.

I also had brush problems with the pump which FASS said was most likely from poor ground. This would have been the problem that I had eliminated with the chassis ground to the pump. In this case it matters not if it is an aftermarket pump or the original pump, the feed is the same.

On my truck the alternator feed is long gone and the fuel pump feed is also not operational. Both circuits have been bypassed with good results.

As you said the book shows a firm ground, my truck did not have a direct ground as the book shows. You may try that on your friends truck, running the positive from the harness and the ground to frame or in your case the engine.

On my harness, the 12 volt was switched, on and off, the ground controlled the voltage level, from I think it was 5 volts at start to 12 volts at run. These were early 24 valve trucks and there may have been minor changes along the way. I now run battery voltate through a relay to the pump and direct ground. It has worked fine.

Sorry for any misinformation.

 

No problem Haulin