Teach me about CP3

[daytripper63]

What exactly does the CP3 do I see the Modded CP3's now and is this needed along with a Fass or Walbro etc.

Where can I go read axactly what this unit does

 

[rbattelle]

The CP-3 is the injection pump. The basic arrangement of the fuel system is as follows:



1. Fuel is pumped from the tank by a small electric fuel pump (just like a gasser would have). Pressure output of this pump is 5-15 psi.



2. Fuel passes through a filter/water separator/heater assembly.



3. Clean fuel then enters the CP-3, where 3 radial pumping chambers pressurize it to the engine demand pressure, which can be as high as 1600 bar (~23000 psi).



4. Fuel under high pressure leaves the CP-3 and is flows into the rail, which acts as a sort of reservoir for distribution to each injector.



The CP-3 is mounted on the drivers side of the engine, immediately adjacent to the power steering reservoir. It has what looks like a small motor with 2 wires going into it - this is called the Fuel Control Actuator (FCA). The FCA is a sort of distribution valve which the engine computer uses to determine how much fuel should be sent to the injectors, how much should be circulated through the CP-3 for cooling, and the remainder is returned to the tank.



The CP-3 is a very high-precision component, which is a nice way of saying it's pretty expensive. It's driven by a gear that meshes with a gear on the camshaft.



The factory service manual offers some good reading on the specifics of the fuel system, as does Cummins Service Bulletin Troubleshooting and Repair Manual ISBe and ISB (Common Rail Fuel System) Series Engines.



A FASS or Walbro does not, in and of itself, require a modified CP-3. Modified CP-3's are for people who are making huge horsepower (or want to make huge horsepower) and need a higher fuel flow rate than the stock CP-3 can provide. FASS and Walbro are both replacements for the pump that transfers fuel from the tank to the CP-3.



Does that help?



Ryan

 

[BimmerAgent]

Well, it sure helps me ! Thanks for the lesson, Ryan. Bruce

 

[daytripper63]

Thanks Ryan, That is exactly what I was looking for.

Robert

 

[Diesel Nut]

When running a Modded CP3, they really like haveing high inlet pressures. Thus, FASS has the availability of models for up to 45-50 lbs of fuel pressure at the CP3 inlet. Helps the CP3 flow more fuel under a load (AKA more power!).

 

[rbattelle]

FASS and Walbro are both replacements for the pump that transfers fuel from the tank to the CP-3.

Of course, the next logical question is, "why would anyone want to replace the transfer pump with a FASS or Walbro (or something)?". There are 3 main reasons:



1. You want to add better filtration and the stock pump can't push enough fuel through a very fine filter (say 2 micron).



2. You believe the stock fuel transfer pump (usually called the lift pump) is unreliable. The lift pump represents a single point of failure for the truck - if it dies, the engine won't run. Lift pumps mounted externally on the engine (pre-2005 trucks) have a nasty history of dying. Lift pumps mounted in the tank (2005 and later trucks) seem to be far more reliable. So much so, in fact, that Dodge now retrofits all 2003-2005 trucks with failed external lift pumps with new in-tank pumps.



3. You want to add a lot more power to your engine, so you need more flow from your fuel tank to your CP-3. A bigger pump does this for you.



Ryan

 

[daytripper63]

Of course, the next logical question is, "why would anyone want to replace the transfer pump with a FASS or Walbro (or something)?". There are 3 main reasons:



1. You want to add better filtration and the stock pump can't push enough fuel through a very fine filter (say 2 micron).



2. You believe the stock fuel transfer pump (usually called the lift pump) is unreliable. The lift pump represents a single point of failure for the truck - if it dies, the engine won't run. Lift pumps mounted externally on the engine (pre-2005 trucks) have a nasty history of dying. Lift pumps mounted in the tank (2005 and later trucks) seem to be far more reliable. So much so, in fact, that Dodge now retrofits all 2003-2005 trucks with failed external lift pumps with new in-tank pumps.



3. You want to add a lot more power to your engine, so you need more flow from your fuel tank to your CP-3. A bigger pump does this for you.



Ryan

I also believe that if you run your rail pressure to low you not only run out of fuel to power the motor but the excess fuel that is normally in the rail is what cools the injectors, so by running the common rail dry or low you can be damaging the injectors as well.

Therefore another need for a stronger lift pump when modding

 

[rbattelle]

I also believe that if you run your rail pressure to low you not only run out of fuel to power the motor but the excess fuel that is normally in the rail is what cools the injectors, so by running the common rail dry or low you can be damaging the injectors as well.

Therefore another need for a stronger lift pump when modding

That's true, but in a sense I think the system is somewhat self-protecting when it comes to this. It's true that if you starve the CP-3 of fuel you can overheat it. But at the same time, if you're starving the CP-3 of fuel the engine probably isn't going to run right (if at all), so you're likely to shut it off and have it towed somewhere for repair before the pump has a chance to overheat.



Considering how many people have lost the lift pump, there are remarkably few CP-3 deaths.



Ryan

 

[ThrottleJockey]

And some people have TWIN CP3 set ups? Is this a belt driven unit?

 

[TMoe]

I am still trying to understand all this fuel flow stuff for cooling injectors. Fuel in the rail doesn't cool injectors. Excess fuel around injectors not used for power may, from what I've read, of course it comes from the rail. This fuel is returned to tank back through line in back of the head along with excess from CP3 directly. There is a spec for return fuel from head line at idle, ? ml per minute, but I don't know how it changes with power being developed. The factory manual doesn't mention anything about fuel for cooling injectors only for lubricating injectors, so lubrication is also important for injectors not just CP. This all relates to flow required vs hp vs what the factory pump can supply. Since the factory pump should be good enough for peak hp and most normal people, excludes most TDR members of course :-laf , won't see peak hp very often the factory pump should be fine. It should also suffice for addition of 2 micron filter kit, similar to GDP, especially in warmer climates. Big line kit, larger lines, etc. , would provide additional margin. I am in Minnesota so this is all TBD.



This may be off topic but has anyone determined how the factory system is affected, flow and pressure, with a large 3/8" fuel delivery system similar to what is supplied with GDP Walbro kits? The factory steel feed line looks small. even smaller than the return line, like the line in the engine compartment. Anyone have a Walbro yet with 75,000 plus miles on it? By now there should be many factory in tank pumps with well over 100,000 trouble free miles, I hope. Not knocking aftermarket stuff just don't want to spend another $500 on upgrading fuel system with a stock truck. If I do get a Walbro I will always have a spare as the simplicity of changing it is it's most attractive feature.

 

[NJones]

TMoe I just had Walbro installed, and used the performance kit because if Walbro fails, I just switch over wires and factory in tank L. Pump is back on line. Probably overly paranoid but now I have 2 lift systems available. Guys, remember, you are not paranoid if everyone IS really out to get you. HaHa.