Brought this from a Differant site...
To all DMAX owners who are reading this thread:
The metering valve shown in this write-up is from a Cummins CP3 and has the triangle ports. The DMAX doesnt have triangle ports, it has rectangle ports.
WARNING...DO NO SCREW UP THOSE RECTANGLE PORTS!!! There are no replacement parts to be had over the counter so if you make a mistake you will either be buying a new CP3 or begging a shop to find you a plunger without raping you.
CP3 Modifications you can do yourself! Many thanks to Relentless Diesel
This should help some of you understand how to modify your own CP3 injector pump. We'll get into more detail of CP3's in another article, but for now understand that all you can do is completely fill the plungers with fuel. The CP3 has three plungers and each plunger intakes a certain amount of fuel and expels it into the fuel rail with each injector pump revolution.
Each plunger makes the same length downward and upward stroke on each revolution regardless of how much fuel is commanded. If the plungers were full of fuel the pump would always move the same amount of fuel per revolution and we know that's not true. At light throttle/low power the pump moves very little fuel into the rail. At high power levels the pump moves all the fuel it can.
It's easy to see that the plungers are not always full of fuel on the intake stroke. Our goal as pump modifiers is to make sure the plungers are more full of fuel (therefore moving more fuel into the rail) during high power levels than the stock pump.
There are several restrictions from the time the fuel enters to the CP3 until it gets sucked into the plunger/barrel chamber. As we eliminate each restriction the plunger chamber can fill more completely with fuel.
This article will cover two simple modifications that most anyone can do to increase the fuel delivery from their CP3 pump.
Take a look at the picture below. You'll notice two easily removable pieces bolted to the back of the CP3.
On the lower right you'll see the fuel control actuator (FCA) which has the black colored electrical connector attached to it. You'll also notice the aluminum housing of the gear pump on the very back. Both of these items are easily removed with the pump still in the truck and cause major restriction to fuel flow.
Remove the FCA first. It will look something like this.
Start with an extremely clean work place.
Using an allen wrench or a cutoff screwdriver pry out the endcap. (We used a torx bit for the pictures, but it deforms the i.d. of the endcap too excessively.)
Carefully remove the spring and lightly tap the fca on the table to help slide the metering valve out. (Use extreme caution when handling the metering valve. If it is bent or even scratched it can stick will be useless.)
All the fuel that is allowed to enter the plungers must first make it through these two tiny triangular holes in this valve.
Each triangle is 0.110" high
and 0.068" wide
for a total area of 0.00748 square inches between the two. This is equivalvent to a single hole with a diameter of 0.097".
By enlarging these triangles more fuel will be able to get to the plungers. This is the smallest restriction from the inlet of the CP3 all the way into the plunger chamber.
We've tried various shapes which allow more or less flow at each duty cycle (position) of the valve and the one that works the best also happens to be the easiest to machine.
A simple dremel tool cutoff wheel can be used to perform a simple slice into the triangle.
**It is extremely important that you do not modify the tip of the triangle. The tip is crucial to the valves ability to stop and regulate fuel at small flowrates (idling, cruising, etc.)**
