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cp3 101 please~


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Hey guys, I was wondering if anyone of you can answer a simple question!

As you may know, I have a Jeep crd diesel. It's pumped with a cp3 for it's common rail.

anyways, there is a heck of a battle on lostjeeps.com about whether or not to 'time' the injection pump during timing belt r+r.

......... some say, rail pressure is rail pressure... others say they want to 'time' the impulse to injector pulses. Which brings me to this point! Are the cp3's a compounding pump, whereas each of the 3 plungers feeds the next one to build up pressure... or are they singly supplying the rail?

are these pumps set up so there is 1 revolution of pump per 1 revolution of engine? (3 pump pulses to 3 required injection events)??

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There is no timing because you are just feeding fuel to a rail. Now some people say that you can get rid of some of the pump noise by moving the shaft of the pump slightly to get harmonics out. Some will also say this will cause then to fail quicker. I have moved one pump and it really quited it down. I dont think it will make them wear out any faster either

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Cool, So, there is no 'want' or 'need' to have the plungers correspond to injector events?

Some on the jeep site are sayin the 'spike' created at the plunger is good when a injector needs it...

Another question! is there a 'dampner' in the fuel rail, to smooth out these impulses? (on the Cummins)

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^^^^ kinda how I look at it too!^^^^

Our jeeps do have a timing mark on the cp3's pulley, but ya know, a 3 piston pump that has 120 degrees separation really doesn't have too much 'spike' anyways!..

interesting on when you move your pump one way or another, you get some differences on 'noise'. You suppose this is the hydraulic harmonics... or you think it's the actual way the engine is responding?

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All three pumping chambers are tied together in one circuit internal to the pump and provide high pressure fuel between 300bar (4351psia) and 1600bar (23,206psia) through a steel line to the fuel rail.

The pump is driven at 2/3 engine speed and is not responsible for injection timing.

The fuel rail stores the fuel for the injectors at high pressure. At the same time, the pressure oscillations which are generated due to the high-pressure pump delivery and the injection of fuel are dampened by rail volume.

The fuel rail is common to all cylinders, hence it’s name “common rail”. Even when large quantities of fuel are extracted, the fuel rail maintains a constant inner pressure. This ensures that injection pressure remains constant from the instant the injector opens to the end of the injection event.

Copied from http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?t=25047 There is a very informative article on the Jeep Liberty CP3 at the link I provided.

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I just found a pic of a cutaway

http://image.dieselpowermag.com/f/tech/1204dp_inside_the_bosch_cp3_injection_pump/35563481+w620/1204dp_04+the_heart_of_common_rail_injection+cp3_pump_diagram.jpg

looks like the 'cam' fires all three at the same time. Man, I was wrong at assuming there was a simple single eccentric rolling the 3 plungers in sequence.

Is there any relief at the end of the rail? pounding liquid down a blind hole seems.. dangerous?? How the heck would you ever bleed air out, just run it until the air is hammered out through the injectors???

Edited by rancherman
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