Attention: TDR Forum Junkies 
This is from Relentless Diesel's website,I thought it might be help shed some light on the cp3 mods.
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It's been a long time since I wrote one of these, but here goes.
The Bosch CP3 High pressure pump is what comes on all 2003 and newer Dodge Cummins Trucks. It is also found on Chevy Duramaxes too and although the orientation of the rail supply fittings and fuel lines are different the capabilities and functions are the same.
The biggest reason I wanted to write this article was to dispel some myths that are developing around this little pump.
First off, let's discuss its theory of operation. Fuel from the fuel tank is drawn out and sent to the CP3 by some variety of lift pump. Pressure is normally 6-10 psi in a stock truck. The CP3's job is to deliver highly pressurized fuel to the fuel rail to which the injectors are connected. The CP3 has no function in how or when or for how long the injectors squirt fuel into the combustion chamber. It's sole job is to deliver fuel.
There is an electromechanical device on the CP3 that the ECM uses to limit the fuel volume that the CP3 delivers. Notice that I said volume and NOT pressure.
I've enclosed a schematic of the internal flow diagram of the CP3 to help some of you visualize what's going on.
#ad
Basically fuel enters the fuel inlet and immediately goes through a 0. 160" orifice before entering the internal gear pump. Pressure increases to 75 psi at the gear pump and is forced through a 0. 110" orifice on its way to the internal pressure regulator.
If the gear pump is flowing more fuel than required by the plungers and barrels then the flow is simply recirculated back into the inlet of the gear pump. It is a very simple system.
The lubrication flow is simply a tiny orifice that lets a small amount of fresh fuel enter the bearing housing of the CP3. The CP3 uses this fuel to cool the bearings and lubricate the internal moving components. This bearing housing is ported directly to the fuel return fitting so this fuel which is now hot from the bearings easily moves back to the tank to be cooled.
Now follow the regulated pressure down toward the flow limiting valve. The flow limiting valve is controlled by the ECM. It uses a variable pulse width 12 volt signal to charge an electromagnet. There is a small valve that is spring loaded to the open position inside this flow limiting valve. The electromagnet pulls the valve into the closed position to restrict fuel flow. The ecm constantly regulates this valve to achieve its desired fuel rail pressures.
If Rail pressures are lower than the computer desires, it simply opens the valve to let more fuel into the plungers and the pressure rises quickly. The same thing happens if the rail pressure is too high. The computer will quickly restrict the fuel flowing into the plungers and rail pressure will quickly fall to the desired level.
At the fully closed position, no fuel is allowed into the plungers at all. At the fully open position, the orifice size of the valve is similar to an 0. 080" hole.
This is by far the smallest restriction inside the CP3.
The fuel then leaves the flow limiting valve and heads towards one of three plungers. The pressure between the flow limit valve and the plunger intake varies widely. If the flow limit valve is closed then there is a vacuum created because the plungers can't stop or slow down. They continue to pump away wildly whether fuel is available or not.
On the other hand, when the computer needs more rail pressure and the flow limit valve is wide open there can be up to 75 psi (full regulated internal pressure) feeding the plungers.
The plungers are too simple to discuss extensively. They simply follow a camshaft and each plunger intakes fuel through a check valve on its intake stroke and pushes fuel through another check valve on its pressure stroke. Each plunger goes through one pumping stroke for each revolution of the CP3.
Now that we've got the basics out of the way we can get on to the more exciting topic of high performance.
It didn't take long for the aftermarket electronic wizards out there to fire the injectors for a longer duration to get more fuel into the engine. It became pretty common place to plug in a single electronic device and gain 180 rear wheel HP. This was exciting for about a week and then the greed started kicking in and everybody wanted MORE.
What we noticed was that when we increased the duration of the injectors passed a certain point the rail pressure would fall off. Our scanners would show that the flow limiting valve was completely open and yet the rail pressure wouldn't increase.
It quickly became apparent that the CP3 had its limit of fuel flow and if you asked for more than it could deliver, the rail pressures fell off. When rail pressures fell, horsepower drops, exhaust temperatures skyrocket and black smoke increases dramatically.
Once a need for a solution developed that's when the vultures of this industry stepped in because they smelled the opportunity for money to be made.
Companies offered tons of useless solutions. Here buy my 120 psi electric lift pump. Pressure isn't the solution you need more volume. No, volume isn't the solution, pressure is. Buy my 95 GPH pump. No 95 isn't enough you need my 150 GPH or it won't work. When that failed then it was you need bigger fuel lines. You need a 3/8" pickup tube in the tank. You need 1/2" lines. You need to get rid of those banjo bolts. The stock fuel filter is not large enough.
The funniest part is those problems are still being talked about even today on internet forums.
To my knowledge, one of my customer's trucks is the fastest commonrail. He's been a 12. 23 e. t. @ 110 MPH @ 7020 lbs. in two different states over a year ago. That truck had a 70 GPH pump that only supplied 4 psi of fuel pressure to his CP3.
That's why I've decided to release some of this info that we've had for over a year now. I'm tired of people making money off unsuspecting, uneducated customers.
Look for a minute at the flowchart above. The biggest restriction is the flow limiting valve itself. It is an 0. 080" orifice.
We dismantled a few and began modifying them. We are able to open that orifice to over . 140" now. That will flow three times what the stock one did. We've even went so far as to dyno test this on a 550HP test truck. The truck gained 5. 8 HP. Barely enough to notice at these levels.
The next orifice is the holes in the gear pump itself. We opened them up as large as the passageways that connected them. No gain on the dyno.
That lead us to believe the plungers themselves were the restriction in the pump. We either had to design bigger plungers or speed up the pump to get more fuel from the existing ones.
Seeing as there are only one or two machines in the world built FOR Bosch to machine plungers to the tolerances required by bosch for reliability and longevity and Bosch oversees the sell of all of them and not to mention the price tag of over $300,000. We decided to go the speed route and leave the stock sized plungers in place.
The most interesting thing was after we got the original prototype built and installed on an otherwise stock CP3 spinning 30% faster, there was NO gain in power or fuel flow.
We then installed our modified flow limiting valve to increase the . 080" orifice to . 140" and the truck gained almost 50 HP. Then we installed our modified gear pump and the truck gained another 36 HP.
It was a long road to finding gains in the CP3 but well worth the effort.
Now I look out at my competition that just started marketing CP3 mods a month ago and they are selling CP3 tweaks in multiple stages. And when customers don't see gains they tell them to buy a different lift pump that will provide 40 psi to the CP3.
I would like to advise this to all interested. Find out exactly what you are buying before you do.
I've heard reports that modified gear pumps and flow limiting valves are going for $1100 from some companies. We picked up only 6HP with that combination.
We also picked up 86 rear wheel PEAK HP with 13-15 psi of fuel pressure. If the pump mods you are buying aren't hitting those numbers. You are being scammed. My modified gear pumps are $192 no core charge. My modified flow limiting valves are $119 + $120 core charge.
These pieces are crucial to making a faster spinning CP3 or a CP3 with larger plungers work correctly, but it doesn't do anything buy itself.
Educate yourself before wasting money.
I hope this has helped some of you understand the mystery lurking inside the CP3's.
Best of luck to you.
The drawings and graphs can be found at www.relentlessdiesel.com in technical section.
--------------------------------------------------------------------------
It's been a long time since I wrote one of these, but here goes.
The Bosch CP3 High pressure pump is what comes on all 2003 and newer Dodge Cummins Trucks. It is also found on Chevy Duramaxes too and although the orientation of the rail supply fittings and fuel lines are different the capabilities and functions are the same.
The biggest reason I wanted to write this article was to dispel some myths that are developing around this little pump.
First off, let's discuss its theory of operation. Fuel from the fuel tank is drawn out and sent to the CP3 by some variety of lift pump. Pressure is normally 6-10 psi in a stock truck. The CP3's job is to deliver highly pressurized fuel to the fuel rail to which the injectors are connected. The CP3 has no function in how or when or for how long the injectors squirt fuel into the combustion chamber. It's sole job is to deliver fuel.
There is an electromechanical device on the CP3 that the ECM uses to limit the fuel volume that the CP3 delivers. Notice that I said volume and NOT pressure.
I've enclosed a schematic of the internal flow diagram of the CP3 to help some of you visualize what's going on.
#adBasically fuel enters the fuel inlet and immediately goes through a 0. 160" orifice before entering the internal gear pump. Pressure increases to 75 psi at the gear pump and is forced through a 0. 110" orifice on its way to the internal pressure regulator.
If the gear pump is flowing more fuel than required by the plungers and barrels then the flow is simply recirculated back into the inlet of the gear pump. It is a very simple system.
The lubrication flow is simply a tiny orifice that lets a small amount of fresh fuel enter the bearing housing of the CP3. The CP3 uses this fuel to cool the bearings and lubricate the internal moving components. This bearing housing is ported directly to the fuel return fitting so this fuel which is now hot from the bearings easily moves back to the tank to be cooled.
Now follow the regulated pressure down toward the flow limiting valve. The flow limiting valve is controlled by the ECM. It uses a variable pulse width 12 volt signal to charge an electromagnet. There is a small valve that is spring loaded to the open position inside this flow limiting valve. The electromagnet pulls the valve into the closed position to restrict fuel flow. The ecm constantly regulates this valve to achieve its desired fuel rail pressures.
If Rail pressures are lower than the computer desires, it simply opens the valve to let more fuel into the plungers and the pressure rises quickly. The same thing happens if the rail pressure is too high. The computer will quickly restrict the fuel flowing into the plungers and rail pressure will quickly fall to the desired level.
At the fully closed position, no fuel is allowed into the plungers at all. At the fully open position, the orifice size of the valve is similar to an 0. 080" hole.
This is by far the smallest restriction inside the CP3.
The fuel then leaves the flow limiting valve and heads towards one of three plungers. The pressure between the flow limit valve and the plunger intake varies widely. If the flow limit valve is closed then there is a vacuum created because the plungers can't stop or slow down. They continue to pump away wildly whether fuel is available or not.
On the other hand, when the computer needs more rail pressure and the flow limit valve is wide open there can be up to 75 psi (full regulated internal pressure) feeding the plungers.
The plungers are too simple to discuss extensively. They simply follow a camshaft and each plunger intakes fuel through a check valve on its intake stroke and pushes fuel through another check valve on its pressure stroke. Each plunger goes through one pumping stroke for each revolution of the CP3.
Now that we've got the basics out of the way we can get on to the more exciting topic of high performance.
It didn't take long for the aftermarket electronic wizards out there to fire the injectors for a longer duration to get more fuel into the engine. It became pretty common place to plug in a single electronic device and gain 180 rear wheel HP. This was exciting for about a week and then the greed started kicking in and everybody wanted MORE.
What we noticed was that when we increased the duration of the injectors passed a certain point the rail pressure would fall off. Our scanners would show that the flow limiting valve was completely open and yet the rail pressure wouldn't increase.
It quickly became apparent that the CP3 had its limit of fuel flow and if you asked for more than it could deliver, the rail pressures fell off. When rail pressures fell, horsepower drops, exhaust temperatures skyrocket and black smoke increases dramatically.
Once a need for a solution developed that's when the vultures of this industry stepped in because they smelled the opportunity for money to be made.
Companies offered tons of useless solutions. Here buy my 120 psi electric lift pump. Pressure isn't the solution you need more volume. No, volume isn't the solution, pressure is. Buy my 95 GPH pump. No 95 isn't enough you need my 150 GPH or it won't work. When that failed then it was you need bigger fuel lines. You need a 3/8" pickup tube in the tank. You need 1/2" lines. You need to get rid of those banjo bolts. The stock fuel filter is not large enough.
The funniest part is those problems are still being talked about even today on internet forums.
To my knowledge, one of my customer's trucks is the fastest commonrail. He's been a 12. 23 e. t. @ 110 MPH @ 7020 lbs. in two different states over a year ago. That truck had a 70 GPH pump that only supplied 4 psi of fuel pressure to his CP3.
That's why I've decided to release some of this info that we've had for over a year now. I'm tired of people making money off unsuspecting, uneducated customers.
Look for a minute at the flowchart above. The biggest restriction is the flow limiting valve itself. It is an 0. 080" orifice.
We dismantled a few and began modifying them. We are able to open that orifice to over . 140" now. That will flow three times what the stock one did. We've even went so far as to dyno test this on a 550HP test truck. The truck gained 5. 8 HP. Barely enough to notice at these levels.
The next orifice is the holes in the gear pump itself. We opened them up as large as the passageways that connected them. No gain on the dyno.
That lead us to believe the plungers themselves were the restriction in the pump. We either had to design bigger plungers or speed up the pump to get more fuel from the existing ones.
Seeing as there are only one or two machines in the world built FOR Bosch to machine plungers to the tolerances required by bosch for reliability and longevity and Bosch oversees the sell of all of them and not to mention the price tag of over $300,000. We decided to go the speed route and leave the stock sized plungers in place.
The most interesting thing was after we got the original prototype built and installed on an otherwise stock CP3 spinning 30% faster, there was NO gain in power or fuel flow.
We then installed our modified flow limiting valve to increase the . 080" orifice to . 140" and the truck gained almost 50 HP. Then we installed our modified gear pump and the truck gained another 36 HP.
It was a long road to finding gains in the CP3 but well worth the effort.
Now I look out at my competition that just started marketing CP3 mods a month ago and they are selling CP3 tweaks in multiple stages. And when customers don't see gains they tell them to buy a different lift pump that will provide 40 psi to the CP3.
I would like to advise this to all interested. Find out exactly what you are buying before you do.
I've heard reports that modified gear pumps and flow limiting valves are going for $1100 from some companies. We picked up only 6HP with that combination.
We also picked up 86 rear wheel PEAK HP with 13-15 psi of fuel pressure. If the pump mods you are buying aren't hitting those numbers. You are being scammed. My modified gear pumps are $192 no core charge. My modified flow limiting valves are $119 + $120 core charge.
These pieces are crucial to making a faster spinning CP3 or a CP3 with larger plungers work correctly, but it doesn't do anything buy itself.
Educate yourself before wasting money.
I hope this has helped some of you understand the mystery lurking inside the CP3's.
Best of luck to you.
The drawings and graphs can be found at www.relentlessdiesel.com in technical section.
Last edited:
:-laf :-laf :-laf
it sure sounded like you were targeting the few who use 40psi to suppliy fuel the cp3!!! as far as fuel pressure goes there is NO WAY you are pushing in more fuel through the rail without increasing pressure in the rail. via cp3 mods, all cp3 mods on the market, in one way or the other ARE increasing constant rail pressure to deliver more fuel. relentless should have told you that before they sold it to you 
:-laf
