Giving an old, worn-out 12V Cummins a few fueling upgrades

While the 12V Cummins might be considered a dinosaur to most in the diesel business, there are still plenty of them out on the road, working job sites and hauling cattle to the auction. The 12V Cummins takes us back to a simpler time, when unhackable computers controlled our engines’ running parameters, and all it took to make power was a little more fuel and the air to support it. The 12V Cummins was an incredible platform back in it’s day, and it can still offer great driving characteristics today with the proper setup. The mechanical P7100 injection pump had endless upgrades to supply fuel to the engine to make just about whatever power levels you wanted. They’ve lost some of their popularity because of later common rail technology, but the dinosaurs aren’t dead.

The Adjuster from Attitude Performance Products (distributed through XDP Diesel) is one of the only power-on-the-fly systems available for the older 12V Cummins-powered trucks. Thanks to an in-cab control knob, owners now have full control of fuel plate travel to adjust fueling output of the P7100 injection. Having the correct fuel rate when you need it means more power, better fuel efficiency, and lower smoke output.

In the past, setting up a 12V to do just about everything was a bit of a challenge. Sure, the injection pump could be built to put out a ton of fuel. The fuel plate and delivery valves could adjust how that fuel was supplied to the engine. However, it was always an all-or-nothing setup that had to then be controlled by your right foot. Today, thanks to the folks at Attitude Performance Products, controlling your fueling output is just a couple clicks away with their new Adjuster—a fully adjustable fuel plate housing that allows complete in-cab P-pump fueling control with the turn of a knob. Much like the adjustable chips found in the latest electronically controlled trucks, The Adjuster allows the driver to make on-the-fly adjustments to the fuel plate and rack travel within the mechanical P-pump while driving. The Adjuster kit comes with everything needed to make a complete install including the fuel armature, AFC fuel arm, cable, in-cab controller, and hardware. The new fuel armature housing can be installed on the factory P-pump just as easily as swapping out the fuel plate, with the addition of running the cable into the cab and mounting the controller.

The controller has 10 settings. You can reduce the pump’s output to below 150cc of fuel (less than stock), or you can crank up to 10 to allow max flow from the pump. The new housing will install between the governor housing and AFC housing of the pump, and it usually takes less than an hour for the complete job. The Adjuster won’t require removal of the pump from the engine. To get everything installed, just get the intake horn and fuel lines out of your way.

The 12V Cummins has long been known for making horsepower. With no electronics to deal with, you just need to increase the available fuel and air to improve horsepower. If you do extensive modifications, the P7100 injection pump is capable of some pretty serious fuel output. However, for the average owner, just a few simple bolt-on upgrades can provide clean, reliable, and usable power to a tired old work truck.
The AFC housing is where all the control happens within the injection pump. It will need to be removed to allow access to the armature arm and fuel plate that will be swapped out for some new machined pieces included in the Adjuster kit.
Before we dive into bumping up injectors, we’ll make some changes on the injection pump to squeeze a little more fuel out of the otherwise stock pump. Starting off with these delivery valve holders, they’ll be swapped out with a stainless steel machined holder from Attitude that offers a consistent .093 orifice size instead of the factory .078 tapered style.
To remove the factory holders, the injection lines running from the pump to the injector will need to be removed, and then a special spline socket will be required to remove the holder from the pump. It’s suggested that you do this one cylinder at a time so as to not mix up or lose parts.
The new stainless steel billet delivery valve holders from Attitude offer a smooth, precise .093 port for increased fuel flow and lower restriction for the fuel to enter the injector. The new holders can also relieve camshaft and roller-bearing stress and reduce wear and tear on the injection pump.

It’s also worth noting: The Adjuster can help increase boost output (3-15psi), lower EGTs (150-250 degrees), improve fuel mileage (+10-25 percent), and increase pump life because you don’t have to always run it at its max potential.

Initial chassis dyno testing showed major changes in overall engine output, with Setting 1 making just 85hp. While not ideal for driving around, this power level could help pump fuel mileage under normal cruising because of the reduction in overall fuel flow from the pump. On that same truck, Setting 4 made a crisp and clean 200hp—more manageable for a towing situation and daily driver looking for smoke-free commuting. Setting 10 on the controller increased to 392hp, which was a bit smoky with a stock turbocharger, but it showed how versatile the Adjuster can make your truck.

The Adjuster will work on any application using the Bosch P7100 injection pump including the ’94-’98 Dodge and 4-cylinder 4BT engines used in many conversion builds. The Adjuster will also work on any vehicle regardless of modifications and power potential. Just looking to improve your stock trucks usability? It’ll do that. Looking to make your 1000-hp drag truck a little easier to drive on the street? It’ll do that, too. The Adjuster from Attitude Performance Products has helped bring the 12V Cummins back from the Stone Age of diesel performance by improving its overall efficiency, drivability, and power potential. Any truck owner should be able to get on board with these kind of results.

New O-rings for the holders were supplied, but you’ll want to be sure to grease the O-ring so it will slide into place without tearing or splitting. The factory valve springs will also be reused here.
Once all six delivery valve holders are installed into the pump finger tight, you’ll want to go through and torque all of them down to 85 ft-lbs.
With the AFC housing removed from the injection pump, you can get a good look at the factory fuel plate setup, which is what controls how the fuel rack within the pump travels to change fueling output to the injectors with throttle input, engine rpm, and boost. This will all be updated and replaced with new parts from the Adjuster kit.
The fuel plate used within the P7100 injection pump will control how the fuel rack within the pump can travel as engine rpm and demand changes. There are many different profiles for these fuel plates, depending on the application. For this project, we opted for the #8 grind, which will offer good fueling for optimum torque output with minimal smoke for towing.
The heart of The Adjuster is the fully adjustable AFC housing insert that allows the fuel plate to be moved forward or backward to control overall rack travel and fueling. This adjustment is made easily within the cab with a knob to be mounted on the dash.
The supplied armature will need to be installed to replace the original armature because the new Adjuster housing will add some height to the assembly as a whole. The longer arm will be required to maintain proper functionality of the injection pump internals.
The new armature is pretty simple to install into the original AFC housing. Once this task is complete, the assembly can be reinstalled onto the new Adjuster assembly and then onto the injection pump for final reassembly
Here you can see the new black, anodized Adjuster housing sandwiched between the injection pump and the AFC housing assembly. Once you’re to this point, all that is left is routing the cable through the firewall and attaching it to the control knob. It will need to be calibrated for full function, but you’re just moments away from shift-on-the-fly fueling for that old 12V Cummins.
The supplied controller was mounted inside the cab directly under the dash. This is a great location because it is within arm’s reach for quick-and-easy adjustments, but it is out of the way from normal driving function.
On the chassis dyno, this old Cummins made a fairly respectable 297hp to the tires. This is well over a 100-hp increase from a factory-fueled 12V truck with this same pump and stock HX35 turbocharger. Having full control over the injection pump offers great drivability and power when you want it, while limiting EGTs and smoke when you are towing heavy over-long grades.


Attitude Performance Products

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