Upgrading Your Diesel Fuel System: Step-by-Step Guide for More Power

Fuel Systems

Adding horsepower for racing, towing, and mileage (yes, more HP often means better MPG) or just for fun will eventually mean you’re gonna need more fuel and more air. Your first performance mods generally should be a good tune, plus a higher flowing intake and exhaust. Once you’ve done that, assuming you have plenty of air available (if not, you’ll need a new turbo here) adding fuel to the mix will be the next step in modification.

So, how do we get more fuel into these beasts? Tuning is the first part, but a good tune can only go so far as the injectors will eventually run out of fuel supply or won’t be able to flow enough fuel due to their factory design. Obviously, adding larger injectors will get the job done, but as I said, they rely on the supply to perform correctly.

There are so many different ways to go about adding fuel, especially since there are so many different types of injection systems in existence today. Simply swapping out stock injectors for bigger ones will not always allow them to perform correctly, so the steps I’ll share with you here are a good way to go about it.

The first step for any engine is removing any weak points in the system. A good example of what I mean here is the fuel rail fittings on a Duramax. They’re extremely restrictive and should be swapped out for a set with larger, ported openings. The Duramax as well as a pressure relief valve that can “pop” and return good usable fuel pressure to the tank, consequently starving the injectors. Some Cummins and Power Stroke engines also have problems similar to these that should be remedied. Getting these issues out of the way will give the next few modifications a good restriction-free and problem-free foundation to work from.

The next step is getting a larger supply of fuel from the tank to the main injection pump. Completely different from Cummins, Duramax, or late-model Power Stroke engines, the 6.0L, and 7.3L Power Stroke’s high-pressure injection pumps are essentially the injectors themselves. While they have a different setup than the rest, the overall theory is the same. So to get the fuel from the tank to the injection pump, a lift pump must be added in line after the tank on the supply line. A lift pump is an electric pump (some big race-only applications have gone mechanical but they’re extremely rare) that is often paired with a fuel filter and water separator. Stock to lightly modified early Duramax owners will see the most performance difference by adding a lift pump alone as until about ten years ago the Duramax never came with an electric supply pump. Its injection pump pulled fuel from its location between the heads all the way from the tank. That’s a long way for a pump to suck fuel from and will create added strain and therefore reduced performance from injection pumps and injectors. This is true for all diesel: Cummins, Power Stroke, Duramax, TDI, Detroit, Cat, EcoDiesel, or any other. While it’s not necessary for lightly modified early model Power Strokes (as they already have a fairly decent pump installed from the factory) it will definitely help and will get the truck set up correctly for the next few modifications down the road.

Now we get to the main injection pump, which supplies the injectors. On a Duramax and later model Cummins or Powerstroke, this comes in the form of a CP3 or CP4. Some choose to add a second pump, which essentially adds double the volume of fuel supply to the system. Doing it this way also means the truck has a second redundant pump, so if either pump fails the truck will most likely continue to run and won’t leave you stranded on the side of the road. A CP3 or CP4 can also be modified to provide more fuel than stock. This is done by increasing the stroke of the piston inside the pump (commonly known as 12mm, 10mm, or stroker pumps). Early model Cummins have different style pumps which can be modified internally similar to a CP3 or CP4. Early Power Strokes rely on oil pressure to force more fuel through an injector. Here a larger High-Pressure Oil Pump would take the place of a larger injection pump for 6.0s or 7.3s as these engines would need more high-pressure oil to run the injectors. Once you’ve gone this far, you’re ready for the last step. Bigger Injectors.

Injector science is different for all engines and can be extremely complicated. No matter how they’re modified, the end result is more fuel flow into the combustion chamber. Once you’ve reached this step, you need to have custom tuning done to control how they inject fuel. Stock tuning will yield less than satisfactory results as modified injectors will flow different amounts of fuel than stock, so their timing and supply pump pressures need to be tweaked for them to work correctly. Sure you can get by with stock tuning and a small set of injectors, but you’ll like the performance with a tune much better.

How far you go down this list depends on what you use your diesel for and the amount of power you need. No matter what you do, please remember that fuel is also used to lubricate and cool injectors; pushing them too far with a less than adequate supply will lessen their life.