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Discussion Starter · #1 ·
so my buddy has a 04.5 cummins he told me is fuel pump, lift pump, and injector pump all went out in a chain reaction and cost him 2200 hes really not my buddy he just kind of a person you listen to and laugh at for a good time ya know what do youall think
 

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First, ask him to clairify:
Injection pump....CP3 = OK
Lift pump... = Obvious
Fuel pump... IF = Gear pump attached to CP3..OK

Yes
A failing/failed lift pump can ruin you CP3.
 

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Discussion Starter · #5 ·
what about the cost though???? is that cheap expensive i like to mess around with him tell him the same thing happend to my truck but it was cheaper kind of thing
 

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Why would a faulty lift pump ruin a cp3 pump, there is no diaphragm to break like in the VP44's
The CP3 is a piston pump (high pressure pump) that relys on the lift pump to "charge it" with fuel (low/supply PSI).

When everything operates correctly, the lift pump supplies more fuel (volume) than is needed to charge the rail.
The excess fuel, supplied by the lift pump, is circulated through the pump case as lube and cooling liquid and returned to the tank.

When there is no lift pump pressure (lack of volume), the rail is given priority, in this condition the CP3 looses lube and cooling fuel flow.
You can run like this for a period of time and never know you have a problem. Hence the importance of a lift pump PSI warning light.
 

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I have NEVER seen or heard of this happening..........I see these trucks every day.The cp3 trucks do not need a lift pump to operate.I have retreived many of them by removing the lift pump to drive them in.
The Duramax does not come from the factory with a lift pump and on and on..............
 

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what about the cost though???? is that cheap expensive i like to mess around with him tell him the same thing happend to my truck but it was cheaper kind of thing
The prices depend on where you buy...........The dealer sells the cp3 for about $2500 bosch rebuilts closer to 1k.
Lift pumps dealer $ 500 aftermarket $200
 

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Fair enough:thumbsup:
I'm I not familer with the "D" maxes.

That is the beauty of this forum...Many different situations and opinions.

I definetly don't know everything.
 

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The CP3 is a piston pump (high pressure pump) that relies on the lift pump to "charge it" with fuel (low/supply PSI).

When everything operates correctly, the lift pump supplies more fuel (volume) than is needed to charge the rail.
The excess fuel, supplied by the lift pump, is circulated through the pump case as lube and cooling liquid and returned to the tank.

When there is no lift pump pressure (lack of volume), the rail is given priority, in this condition the CP3 looses lube and cooling fuel flow.
You can run like this for a period of time and never know you have a problem. Hence the importance of a lift pump PSI warning light.
Excellent description and bang on.
True the Duramax doesn't have a lift pump (most applications) but it also doesn't have anything interfering with the fuel flow from the tank (like a failed lift pump).
If your lift pump has failed or is failing and causing a flow restriction it could definitely cause a lack of lubrication and overheating to the CP3 pump.

I've heard of way more failed CP3 pumps on the Cummins compared to the Duramax...
 

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Why would a faulty lift pump ruin a cp3 pump, there is no diaphragm to break like in the VP44's
While that's very common that's not the only thing a bad lift pump could do to a vp44.
The lack of lubricating fuel also cause vp44 pump seizing and pump module failing due to excessive heat.
Bad news all around.
 

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Excellent description and bang on.
True the Duramax doesn't have a lift pump (most applications) but it also doesn't have anything interfering with the fuel flow from the tank (like a failed lift pump).
If your lift pump has failed or is failing and causing a flow restriction it could definitely cause a lack of lubrication and overheating to the CP3 pump.

I've heard of way more failed CP3 pumps on the Cummins compared to the Duramax...
Thank You for the clairifacation :yourock:
 

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when i first read the post cp3 failed due to bad lift pump i thought that i should panic and test my lift pump pressure, but after thinking about this i relized that many aplication using the bosch cp3 pump do not use a lift pump and some can suck fuel up to 5 feet!

if the cp3 pump is being fed good fuel. (air tight suction line) the gear pump on the rear of the cp3 should be plenty enough to feed the cp3.

insead of monitoring lift pump pressure you should be monitoring the cp3 charge pump pressure, the bosch specs i use is at full load, no less the 72PSI.

if that number starts to fall then i would start looking for higher flow lines or air leak into suction line.
 

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Where can you tap in to the chamber between the gear pump and the radial piston pump? Is there a port by the FCA?
I know the gear pump can produce around 200 psi to force fuel into the piston pump.
 

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reading all this makes perfect sense, but is it possible for a lift pump to fail and block fuel from getting to the CP3, which would then starve it/run it dry and seize?
 
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