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P7100 Injection Pump Tuning

Fuel Plate

You will want to grind the fuel plate, or maybe just buy one from a performance shop. Dynomite Diesel Performance, Banks, and TST all make aftermarket fuel plates.

Governor Spring

Another good mod is the governor springs.


You can avoid this by purchasing a set of 60 PSI valve springs. The stock setting allows the engine to rev to 2750 RPM, but they start to limit power at 2250 RPM or so. There are also 3K, 4K, and 5K Governor Spring Kits for sale by performance shops too. A 3K will fuel to 3000 and rev to 3400. A 4K will fuel to 4000 RPM and rev over that. 5K GSK's are for pullers and require extreme modifications to the engine to not be damaged. If you feel like you want the 4K GSK, but don't have the valve springs yet, buy a 4K and leave the smallest spring out. It will run like a 3K. You can use the instructions for shimming the springs to change them.

Delivery Valves

Another item that could use modification on the pump is the Delivery Valves. Stock DV's on 96-98 autos and 94-95 rigs are 131's. Stock on 96-98 rigs are 181's. There are also 191's, and there has been discussions about using 131/181 hybrids, although the gains are small. Beyond that, there are 022's, 024's, full cuts and lazer cuts. There are some more, but these are the ones you will usually find on most rigs. lazer cuts don't have shoulder material like the other ones, so they turn off the fuel gradually rather than instantly like most DV's. They smoke more and run hotter, not to mention the loss in economy. DDP and some other performance manufacturers also have their own style of DV's.

AFC Adjustment

Staying on the injection pump, next will be the Air/Fuel Control or AFC. This unit is set up to give you so much fuel per pound of boost. The Star wheel is located under a hex plug on top of the AFC unit. Tightening it increases the amount of boost to get a certain amount of fuel. Loosening it will give you more power sooner, but at the cost of smoke (if you think of that as a cost). The arm that hangs down can be modified by grinding the foot of it flat. You can also purchase different springs and washers to put in the AFC for adjustments to fueling potential.

Rack Plug

After you've modified the Fuel Plate and AFC, you may want to get a 2095 Rack Plug aka Mack Plug. The 2095 plug has a 2mm deeper well than the 2000, allowing the rack to travel further increasing power. You can get one at your Cummins dealer for about $15. They will provide a greater increase in horsepower if you already have more power to begin with. 500hp motors will gain about 20-30hp, while 300hp motors will gain only 10-15hp. Again, this only works if you have an aggressive plate and a modified AFC arm.


One last mod to the pump is timing. Stock timing is 12.5° in 94-95's, 14° in 96-98's. You can adjust it to 16.5° with the stock head gasket. You could go up to 20° with aftermarket head gaskets. Advancing the timing allows better economy and more power, as well as where in the RPM range you get the most power.


Next we'll talk about injectors. Stock 94-95 autos are 160hp. 94-95 manuals are 175hp. 96-98 autos are 180hp. 96-98 manuals are 215hp. There are also 300, 330, and 370 hp injectors from Bosch. But there are lots of choices. Bosch 370's are designed for marine applications and don't have the correct spray pattern. Running them won't hurt your motor, but they haze at idle, smoke a lot, and run warmer than comparable size injectors of other brands. New Era makes correct spray 370's as well as 435 hp injectors. DDP stage 3's are like 370's, and DDP 4's are like 435's. To get the full horsepower out of 435 injectors, you will need more air. If you add too much fuel without more air, you drown out the fire.

Lift Pump

Once you get the pump going and some bigger injectors, you may find that your fuel system can't keep up with the demands. The stock lift pump will only take you to about 500-550hp. One of the more popular options is to purchase a Fuel/Air Separation System or FASS. FASS pumps have higher gallons per hour rating, and they ensure that no air is sneaking into the system through the fuel.

Article Wrote by: Cummins Power @
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