Good reading on the CP3 injection pump

MightyCRD · **Posted:** Thu Aug 09, 2007 1:16 pm

This article was found here: http://www.oilburners.net/forums/showthread.php?t=9534

Good reading - here it is reposted - this is aimed toward Duramax and Cummins diesel owners, which also use the CP3 injection pump. Looks like their is a lot of info, but not specific to us. I hope that this helps .....

BEGIN REPOST - a big thanks to CTD who wrote this ....

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.

cntrline36 · **Posted:** Thu Aug 09, 2007 8:19 pm

Good read! Thanks!!

retmil46 · **Posted:** Fri Aug 10, 2007 5:02 am

Yep, it's a good read.

And dead wrong. Read the FSM for how the pump actually works.

DZL_LOU · **Posted:** Fri Aug 10, 2007 8:46 am

retmil46 wrote:

Yep, it's a good read.

And dead wrong. Read the FSM for how the pump actually works.

Agreed

MightyCRD · **Posted:** Fri Aug 10, 2007 9:29 am

Mods - please delete post for misinformation. Thanks!

UFO · **Posted:** Fri Aug 10, 2007 10:53 am

retmil46 wrote:

Yep, it's a good read.

And dead wrong. Read the FSM for how the pump actually works.

How is the post contradicted by the FSM? You can't add a pusher pump to feed it?

(and it may be useful to leave this post, and document how it is wrong, so folks don't assume it's correct on some other site...)

gmctd · **Posted:** Mon Oct 01, 2007 8:42 pm

Only thing I see wrong with this is the housing pressures, which are prolly correct for the 6.6L V8 DMax - anybody else wanna detail further differences?

IMO it's a good read in conjunction with the CRD FSM

retmil46 · **Posted:** Tue Oct 02, 2007 5:26 pm

It's bulls##t. The CP3 DOES NOT starve itself of lubrication to feed the high pressure side. Read the FSM, first priority is the pump supplying itself with lubrication and cooling flow. This guy had it bass ackwards, good thing he admitted at the beginning of the article he really wasn't up to speed on any of the manuals for it. If you find the forum where it was originally posted, this article ended up getting shot down in flames.

gmctd · **Posted:** Tue Oct 02, 2007 6:04 pm

I read thru it again, and the indication is that if the fuel supply is restricted and the CP3 is starved, there will be no internal lubrication - very true - a danger in the Dodge systems if the external lift pump is damaged, but also in the non-external lift pump systems in the DMax and Jeep CRD - if the fuel line becomes blocked - or just goes empty.

Running around town, the engine would of course die rather quickly - it's a stretch in the flatlands, but in certain terrain where engine braking is required to manage the load on long inclines, the CP3 could be damaged in a long brake-down.

Could also happen in a racing event - pump damage while the rpms are dropping - CP3 don't stop when the key goes off, only when the crank stops turning - the CP3 is 1:1 on the crank, at 6000rpm.

He was a little off on COV supply to the FQV, but according to the FSM, it does supply full fuel to the FQV during low rpm cranking so the engine will start, but is not supplying lube to the entire pump - in that mode, the engine would run with minimal fuel, and if inlet fuel was starved such the COV could not regulate, that could result in internal damage.

ECM would probably step in at that point and shut things down due to low rail pressure

I agree - it could be better - I've been surfing the 'net since reading that, trying to find some official info on the CP3 - not much out there except Bosch-sponsored-for-pay training seminars - fortunately I also have the smattering of info from the FSM.

If you guys haven't found anything, maybe I'll re-write it so it will be a good read

BTW - I often get 'page cannot be displayed' from this site, so I don't have input from that link.

Good reading on the CP3 injection pump

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