Understanding the CP3 fuel pump(D-max and Cummins)

[Whit]

Article by CTD

Disclaimer
I have no CP3 Bosch training manuals, training videos or service manuals, I dont know how to use the internet nor am I capable of thinking on my own.

I am asking for a D-max guy to help me understand how the CP3 fuel pump works in their application without the use of a lift or pusher pump. The fuel injection pump on the 3RD gen Dodge/Cummins is a CP3, this is the same pump used by the Duramax Diesel, If you own a 3RD gen Dodge you need to understand this.

Understanding the CP3.

The CP3 is a 3 piston metered inlet pump. By metered inlet that means that the Fuel Control Actuator valve controlled by the ECM meters fuel going into the pumping chambers to control how much fuel the CP3 pumps and thus the engine rail pressure. This is in sharp contrast to other pressure control systems that divert large amounts of PRESSURIZED flow OUT of the pump back to the tank. The FCA meters how much fuel actually gets pressurized in the first place. Very neat and efficient.

In order to meter the fuel into the chambers, the CP3 has an internal metering/lift pump built right into it. This pump takes the fuel at supply pressure and boosts it to pressures between 80 and 180 PSI depending on what is required. This fuel is fed to the FCA via the cascade overflow valve located on the side of the pump.

The cascade overflow valve's (COFV) purpose is to prioritize the fuel flow between the pump itself (ie feed the FCA), then flow excess fuel to the lubrication flows to cool and lubricate the pump and finally divert any flow above that to the return line.

The COFV prioritizes the flow in that order. If the flow rate is low, only the FCA will get fed. No cooling or return flow will be provided. If the flow rate increases, the pump will get cooled. Any more flow than that and some fuel will get sent out the return line. Note that this prioritization happens AFTER the internal supply pump and there is NO passage from the CP3 inlet to the CP3 return line. The inlet feeds the internal supply pump. Unlike other pumps where the fuel supply pump inlet may feed the interal cooling passages and make its way back to the return line.

BTW: The Dodge shop manuals say the COFV isn't "field serviceable" they have been removed before, disassembled and re installed with no problems.

So... the internal supply pump is a constant displacement gear pump. This pump is actually capable of developing enough suction to draw fuel through a filter right from the tank. It actually does this on Duramax installations.

Being a constant displacement pump means that it you can't hook just any supply pump up to it. Whereas an injection pump like a P7100 can tolerate a large difference in flow rates to/through it with relatively little pressure change, the CP3 cannot. If you try to push too much fuel to the CP3, the pressure will skyrocket. There are no internal relief valves in the CP3, only a direct feed to the supply pump. Conversely, if there isn't enough flow to it, the pressure will drop and the supply pump may actually start developing a vacuum in an attempt to get enough fuel.

Supplying the CP3

Users needn't worry about pushing fuel to a CP3 at a high pressure. Because it has a built in supply pump, the CP3 only needs to be supplied at a low pressure OR VACUUM and it will handle supplying the pumping chambers from there. Whereas previous pumps had to be somewhat pressurized, the CP3 handles its own pressurization.

Conversely, users do have to worry about getting enough fuel to the CP3. Remember the COFV ? It prioritizes the flow and when there isn't enough fuel to the CP3, it shuts off internal lubrication and cooling flow. This is very bad news for the longevity of the CP3. Diesel fuel viscosity and lubricity falls dramatically with an increase in temperature. Hot fuel within the CP3 is bad.

Basically, one needs to get enough fuel from the tank to the CP3 inlet to keep the CP3 well fed, yet not over pressure it doing so.

I get very nervous when I read of users having their inlet fuel pressure at the CP3 falling to zero PSI. While the CP3 is capable of sucking fuel from the tank in the Duramax installation, in the Dodge installation there is a restrictive fuel pump between the CP3 and the tank. Thus when one sees 0 PSI at the inlet of a CP3 in the Dodge, it is or is on the verge of starving.

 

[Distinctive Dave]

Thats some great reading for a new dodge owner like myself. Thanks for the excellent write up.

 

[cerberusiam]

Being a constant displacement pump means that it you can't hook just any supply pump up to it. Whereas an injection pump like a P7100 can tolerate a large difference in flow rates to/through it with relatively little pressure change, the CP3 cannot. If you try to push too much fuel to the CP3, the pressure will skyrocket.

So, what happens when the pressures spike to the inlet? Is there immediate damage that cna happen or is it more of a long term problem? Seals in the pump that won't take a lot of pressure? There seems to be a large disagreement on whether the CP3 will take high pressure or it is much happier with just flow. I have hear 16 psi max to the inlet with about 45 gph flow needed for a adequate fuel and cooling on a stock system. Any info that would contradict this or expand it? Thanks for the article, its a great start.

 

[holtzer1]

we have hooked many a FASS systems to the new pumps...they have a fuel presure valve that keeps everything in check.

 

[Whit]

You will be fine at 16 psi..................but I wouldnt push it much past that the stock lift pump is suppose to push out at MIN 11.5 PSI. All the books says for the GPH is that the flow is sufficient to supply the injector pump. It draws 5 amps at max flow and is 100% duty cycle. I still havent read what the flow requirments are though............. More info for this that may help the understanding of the CP3 is in the(FCA)Fuel control actuators job is to control the amount of fuel entering the low pressure side of your injector pump. It is a solnoid operated valve located on the bottom driver side of your pump. The ECM controls the action of this valve. Fully open and it has full flow of fuel into the High pressure side of the pump............. closed and it will shut off the fuel supply.. Why is this important? After talking to a my local Cummins guy in Riverton about some issues one thing that he brought up about the FCA and it having premature wear on it. This casuing it to not work properly. If the ECM is demanding that fuel be stopped and it is getting by the FCA then this is casuing to much fuel to enter the high pressure chambers via the internal lift pump inside the CP3 that feeds the high pressure 3 piston pump.
The over flow valve is another problem area that seems to be casuing a few problems........... If this valve gets dirty and cannot open then fuel pressure cannot bleed off and you will get a pressure spike. Although this is unlikely.
If the opposite happens and the valve will not close properly then you will have a loss of pressure in the Injector rail system. this in turn will result in poor fuel economy, loss of power and also a incomplete burn as the injectors will not be able to give the proper amount of fuel into the chamber.
Next is the Fuel Pressure sensor. It controls when the over flow valve will open and close. both the sensor and the over flow valve are mounted on the fuel rail. If this sensor fails then your truck will go into limp mode or wont run at all.............. The sensors are pretty reliable from all my reading........... but they are the key to the whole system.
The fuel filter is good down to 10 microns so this is key to maintaining the overall fuel delivery.......... A few of the dealerships have stated that injector wear is from poor fuel filtration............Yet non of them have been able to state what level of filtration is needed to keep this wear from happening, I truely believe the wear is being caused from the low sulfer fuel and the refineries not doing adiquate lubricity replacment, Illflem told us the other day that a 1% biodiesel supliment will increase the overall lubricity by 60%, I only wish I could get some bio here in Wyoming

I also found some very good reading on what our low sulfer fuel is or isnt doing for us............Check it out here, Robert Bosch was involved with it so we had representation , the ling is long but well wort the read, scroll down a bit and look at the pics of internal pump parts and you will be shocked to say the least

http://www.arb.ca.gov/fuels/gasoline/meeting/2003/022003bosch.pdf

 

[Whit]

Thanks to Devon Wyatt for some real good info on fuel systems.


1. The stock lift pump is suppose to push out at MIN 11.5 PSI. All the books says for the GPH is that the flow is sufficient to supply the injector pump. It draws 5 amps at max flow and is 100% duty cycle.

2. Fuel heater if not wroking properly can cause wax build up (unlikely unless in very extreme cold weather ie -30 cels or below), or may cause blue and or white smoke.If the fuel is below 45 F +/- 8 F the fuel heater will turn on and then turn off once the fuel temp in the element reaches 75 F +/- 8 F. Cold Fuel will cause white smoke. Interesting. I truly wonder what the reflashes are from DC to fix these symptoms. Are all they doing is changing the heaters parameters to preheat the fuel?

3. FCA fuel control actuator. It's job is to control the amount of fuel entering the low pressure side of your injector pump. It is a solnoid operated valve located on the bottom driver side of your pump. The ECM controls the action of this valve. Fully open and it has full fow of fuel into the High pressure side of the pump. closed and it will shut off the fuel supply.. Why is this important? After talking to a few mechanics about some issues one thing that was brought up about the FCA and it having premature wear on it. This casuing it to not work properly. If the ECM is demanding that fuel be stopped and it is getting by the FCA then this is casuing to much fuel to enter the high pressure chambers, this in turn will cause to much fuel to be routed to your injector rail. At the end of the day how does this effect a person. To high of a pressure and the end result is leaking injectors. because the fuel pressure is to great with in the rail system.

4. The over flow valve is another problem area that seems to be casuing a few problems with in some of the newer trucks. If this valve gets dirty and cannot open then fuel pressure cannot bleed off and you will get a pressure spike. Although this is unlikely.
If the opposite happens and the valve will not close properly then you will have a loss of pressure with in the Injector rail system. this in turn will result in poor fuel economy, loss of power and also a incomplete burn as the injectors will not be able to give the proper amount of fuel into the chamber.

5. Next is the Fuel Pressure sensor. It controls when the over flow valve will open and close. both the sensor and the over flow valve are mounted on the fuel rail. If this sensor fails then your truck will go into limp mode or wont run at all. The sensors are pretty reliable but they are the key to the whole system.

6. The fuel filter. Still not sure as to the actual micron it filters down to. I beleive it is 10mic's. A few of the dealerships have stated that injector wear is being casued by poor fuel filtration. Yet non of them have been able to state what level of filtration is needed to keep this wear from happening.( cant blame them neither can DC). One thing I do know is that three out of 4 dealerships said that Shell has the best fuel additive package for Diesel fuel. Since they hve been using them they have noticed a difference in power and economy.
kinda makes a guy wonder if it is the actual dirt in the fuel or if it is the amount of water in the fuel. Water at pressures of 20,000psi can cut steel. So if water does get by the filter system can and is this causing the problems with some of these trucks? Not sure would be good to find out.

Not sure if this helps any one out at all. I have been told to look at the FCA and also over flow valve for signs of wear. If found then bring into the dealership to have them investigate further.

I found this and thought it would be of some assistance to add to this thread, also we have a new member 03CTD who claims to be the original author of this tech article, I have no clue where it originated from just found it to be informative

 

[Wyatt Earp]

Whitmore,

I've been made aware of this posting and figured I chime in to address something. Opinions are a great thing and but must ask why did you post this information as if it were your own? It seems you have caused a few people to get their undies in a knot over at DieselRam.

For the record CTD has had many problems with his truck and has done exhaustive amounts of research to attempt to solve his crappy mileage and his injection troubles. He deserves to be thanked for his efforts. He has asked me a variety of issues with regards to fuel as well as filtration of it.

I have no issue with you or this post but would appreciate it if we could keep it on the up and up from now on.

Yes, these trucks have issues with their fueling but this will likely change with the new regulations coming in 2007 along with the ULSD. Some say it will be worse while others claim there will be no adverse effects. I think that the jury is still out on that one as it is in the future. That said, I personally think that it is going to cause more than a few problems for the computer controlled / electronic injection systems out there made before 2007 if no extra lubrication is run through regularly. Time will tell I guess...

All the best on the rest!

Cheers

 

[Wyatt Earp]

Hold on there... Wikked (et all) If I came across as big headed, my appologies. CTD is a friend of mine and he has been as I've said experiencing problems with his 3rd gen truck. Where he came across this information is not for me to say, rightly or wrongly.

I am no Mechanic, don't have a degree in Fluid Dynamics, Hydrology or Mechanical Engineering but have had enough first had experience with fuel types, additives and such that I feel that perhaps my experiences would help those whom care to read about it.

I think we are all here to help each other.

Can't we just all be friends?

Cheers

 

[03CTD]

After reading the post over again I notice that a few changes have been made to it since yesterday. My original post's are #5 and 6 of that article. I notice a few name changes and that but all and all it is the same write up that I did.

I just want people to understand that the info is good and I think we all encourage it to be used by as many people out their. But please ask permission first before posting it as your own. That is all that I am saying.

As for proprietry rights on the CP3 and that. No I do not own them nor claim that they are mine. Nor claimed to have written the book on the operations of such. The disclamimer on the book's I used for research is for info only. And the mechanics I have talked to have been freely open about the workings of the system. The same info can be found on many different books to due with the CP3 and Vp44 pumps.

Do I care that a person has copyied and pasted then changed out a few names to fit his bill. Yes!! They should have asked permission from the web master and then posted it as it was written. Not as if it was their own doing.

At the end of the day am I mad no. But it is the general point of honesty that I am addressing here.

I wish we could pass beer over the net. I would hand one out to everyone involved in this.
Sorry if I made this into a bigger deal then it is. It just shocks me thats all.

Cheers

 

[03CTD]

Guys sorry about getting off on the wrong foot here. I look forward to future reading on this site.

Cheers

 

[rubberfish]

Holy crap Kevin
You've really gone and done it now.