Engine/Transmission (1998.5 - 2002) Ever seen lift pumps do this?

[OTRPU]

I don't know the pressures, but had one cruise along just fine then all at once engine died. Restarted and ran along fine agian, then died again. Did this all the way back to Colorado, bout 500 miles. Called my Denver DOC enroute. . . he said it sounded like a pump to him. Ended up replacing the lift pump & injection pump.



Cheers,

OTR PU

 

[LarryM]

c-hawk, I have had the exact same symptoms when my pumps failed, (note that I said pumps plural). I have replaced 4 so far. The original lasted the longest, then the next three replacements lasted only 4,000 miles, give or take a few. I got these replaced under warranty from Cummins, although they didn't like it. They only replaced the pump, I did the work to change them out. In EVERY case, the failure was in the motor end, not the pump. I took them apart by cutting the crimp and found that the bushing on the motor end was really bad, causing the armature cock and rub the poles causing the motor to load up and slow down. In each case, there was absolutely NO damage or wear in the pump, the vanes and rotor were perfect, not even a polished wear pattern. My fuel filters and canister are always really clean. The pump that is in the truck now has over 25,000 on it and it is running like new, 14. 5 idle and won't drop below 10 WOT. I have done nothing to the truck except replace the pumps. I took the bad ones to Cummins, and they acknowledged the wear in the bushings and said that they would forward them to their tech rep. Anyway, when I went to them to get the last bad one replaced, they asked if they could run a check on my truck, to see if I had any problems that caused the pump failures. They checked it thoroughly for 2 hours and found none. So, at least in my experience, the pumps are faulty, and the fault lies in the electrical end, and I can't tell you why this pump has lasted so much longer than the others. Maybe a different lot, who knows. Anyway, for what it's worth..... good luck



Larry

 

[Gary - K7GLD]

In EVERY case, the failure was in the motor end, not the pump. I took them apart by cutting the crimp and found that the bushing on the motor end was really bad, causing the armature cock and rub the poles causing the motor to load up and slow down. In each case, there was absolutely NO damage or wear in the pump, the vanes and rotor were perfect, not even a polished wear pattern.

*Really* good info Larry!



Not enough owners go the second mile to see *why* these LP's fail way too early - your info adds to the knowledge base, and gives better insight into these failures!

 

[rweis]

Built on monday?, or friday?



I second Gary's comments, the ONLY way to find out WHY, open it up.



Bob Weis

 

[c-hawk]

Larry,



Thanks for the information. I'm hoping i've got a good one this time. If it fails i'll disect it and see why.



Thanks again to everyone that responded.



Chris

 

[CFAR]

1st pump <10,000miles - No pressure - Mechanical failure,

2nd pump <10,000 - 30,000miles - Gradual failure, low pressure, 0psi under load

3rd pump 30,000 - 111000miles - Getting a little low on pressure, just under 10psi max load.



I'll replace this one soon, keep the 3rd pump as a back up to replace 2nd pump which is back up now.

 

[NoSeeUm]

c-hawk, I have had the exact same symptoms when my pumps failed, (note that I said pumps plural). I have replaced 4 so far. The original lasted the longest, then the next three replacements lasted only 4,000 miles, give or take a few. I got these replaced under warranty from Cummins, although they didn't like it. They only replaced the pump, I did the work to change them out. In EVERY case, the failure was in the motor end, not the pump. I took them apart by cutting the crimp and found that the bushing on the motor end was really bad, causing the armature cock and rub the poles causing the motor to load up and slow down. In each case, there was absolutely NO damage or wear in the pump, the vanes and rotor were perfect, not even a polished wear pattern. My fuel filters and canister are always really clean. The pump that is in the truck now has over 25,000 on it and it is running like new, 14. 5 idle and won't drop below 10 WOT. I have done nothing to the truck except replace the pumps. I took the bad ones to Cummins, and they acknowledged the wear in the bushings and said that they would forward them to their tech rep. Anyway, when I went to them to get the last bad one replaced, they asked if they could run a check on my truck, to see if I had any problems that caused the pump failures. They checked it thoroughly for 2 hours and found none. So, at least in my experience, the pumps are faulty, and the fault lies in the electrical end, and I can't tell you why this pump has lasted so much longer than the others. Maybe a different lot, who knows. Anyway, for what it's worth..... good luck



Larry

Thanks Larry



I have read this same line of thought some where else and have thought about it some. That the problem is really the bushing failure that is the culprit of the stock LP failures.



To my experience in industrial pump failures, about 90% of the time it is a bearing failure. By that I mean that the actual bearing may or may not have initiated the failure, but for whatever the cause it was the bearing that took the beating and quit.



Normally you would see the highest D/P (differential pressure) across a pump at minimum flow. This D/P (to simplify) effectively exerts radial and or axial thrust against the pump surfaces and hence the bearings. In the case of the stock LP the D/P across the pump may actually increase as the flow increases due to the fact the the suction pressure is dropping also.



As an example:

@Idle suction pressure = 0 psi discharge pressure = 15 psi D/P = 15 psid

@WOT suction pressure = -5 psi discharge pressure = 11 psi D/P = 16 psid



Additionally, the stock LP is mounted to the ultra-smooth vibration free running Cummins (at least mine is ) which could raise the bushing thrust force beyond tolerances.



What leads me to believe this is that from what I have read, is that simply moving the Carter to a frame mount adjacent to the tank increases life.



Jim