banshee

The ECM simply quits firing the injectors. No fuel, no fire.

The FCA [Fuel Control Actuator] controls the volume of fuel that gets passed to the high pressure 3 piston pump chambers. The FCA gets fed a metered pressure of fuel (75 psi that is set by the Cascade Overflow Valve) and adjusts pressure with a linear valve. Full open = max pressure, full closed = idle pressure. There are two small holes in the valve to allow a small quantity of fuel to pass when the valve is "closed".

The fuel is pulled in through the inlet and directly passed to the LP gear pump on the back of the CP3. From there it gets pressurized to a max of ~180 psi. The fuel gets directed to the fca where it tees and gets regulated by the Cascade Overflow Valve to 75 psi. All excess fuel gets directed either to A) Lubrication Passages or B) return line by this valve. It is a spring and plunger device and regulates the fuel based on how far the valve opens. The fuel that does make it through the FCA goes to a central ring in the pump and is delivered to one of the three main pump chambers. Upon the downstroke of the piston the fuel is sucked in through a one-way delivery valve and then is pressurized and expelled through another one way valve. Once it exits this chamber, at ~5,000-23,000 psi, the fuel is combined into one common outlet that directs the fuel to the rail. The rail has an overpressure relief valve (pops at ~27,000psi) and the injectors have another return for fuel they don't inject. The only bypass in the CP3 is Cascade Overflow.

Not sure what you mean by this? Obviously the ECM must receive an 'on' command from the keyed ignition, and it needs timing data from the crank/cam sensors. The FCA receives info on how much to open from the ECM. The ECM decides this by monitoring the APPS level, the Rail Pressure Sensor, and MAP sensor at the least. The FCA opens more or less to make the rail pressure sensor value match the ECM's "command value".

A pressure box affects the rail pressure sensor's delivered value. As stated above, the FCA opens and closes to try to make the rail pressure sensor match the ECM's commanded pressure. A pressure box effectively intercepts the Rail Pressure Sensor's value (a voltage delivered on a set schedule to interpret pressure on a 0-5volt scale) and lowers this value. In other words, if the rail is really at 23,000 psi (full throttle) the pressure box sees this value, clips it, and reports a false 19,000 psi signal to the ECM [NOTE: that number is made up just for the sake of argument. That real number probably varies]. The ECM sees this and knows that the 19,000 psi doesn't match it's target value of 23,000, so it holds the FCA open even more. Eventually the pressure rises high enough (26,000? psi) so that the pressure box 'clips' that value back to 23,000, thus matching the ECM's desired value.

Pictures really are worth 1000 words for the CP3 internals. I have one torn apart in the garage and should really take a bunch of pictures and make a "Get to know your CP3" thread.

John

XLR8R

Thanks for such an informative post, John - and I can't wait to see those pics!

03 ant a hemi

The rail has an overpressure relief valve (pops at ~27,000psi) and the injectors have another return for fuel they don't inject. The only bypass in the CP3 is Cascade Overflow.

Another question where is this return for the injectors? Is it internal?
I know their is a return passage that exits at the end of the block by #6 injector but how does this fuel get returned if their is only one tube running to the injectors, and is suppose to be a seal.

Cheers.

banshee

Yes, the injector return pops out on the back of the head, and a return line connects that, the rail pressure sensor return, and the CP3 return line into 1 line near the fuel filter canister. The internal passage in the head opens up to all 6 injector bores and connects to the main line that exits out the back. there is no direct sealing line since that returned fuel is basically under no pressure. The small cavity between the copper washer and the oring serve as the return reservoir. When the injector is out of the bore you can see it if you look down into the bore.

XLR8R,

No problem. I'll try to quit being a slacker and get out to take some pictures.