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DieselSite CPR Fuel System - Out With The Bad Air

Project Old Soldier Gets A Regulated-Return Fuel System For Better Flow, Filtration, Cooling, And Air And Water Removal

Christopher Campbell
Sep 1, 2010
Photographers: Christopher Campbell
One of the real keys to longevity for any engine is not simply maintenance, but also identifying and improving factory design flaws that actually work to decrease reliability and lifespan. The fuel system in our project truck affectionately known as Old Soldier is unfortunately one of those defects. We're not saying a 7.3L can't last a few hundred thousand miles on the stock system. Obviously, many have, but the odds of doing so without major repairs along the way are greatly increased by improving the fuel system.
Photo 2/35   |   DieselSite's CPR fuel system is a B-100 biodiesel-compatible regulated-return upgrade, but it also includes in-tank fuel pickup mods, a pre-pump filter, return line cooler, Aeromotive pressure regulator, and new braided stainless fuel delivery lines. It's an all-or-nothing deal, since DieselSite will not break the system up into modules, as Bob Riley has found that adding components a few at a time can cause more issues than it fixes. Actually, to qualify for tech support, DieselSite requires that any previous fuel system mods be removed.
So what are the problems? There are actually three: aeration, filtration, and flow. Besides the standard diesel foaming issues that can introduce air, there are several leaks in the stock system that allow air to creep in, at best creating a noisier engine and at worst damaging the fuel injectors. Either way, it's almost certainly compromising efficiency, since air is compressible and can actually affect injection timing when caught in the injectors, which usually results in loss of power and decreased mileage. That same trapped air can also damage the tip and plunger assembly, causing the injectors to wear out prematurely. Ever check the price on 7.3L injectors? Plus the cost to install them? Don't-it'll scare you.
Unfortunately, the stock returnless fuel system has no provisions for evacuating the air, which is one of the prime reasons for stepping up to a regulated-return-style fuel system, such as DieselSite's CPR line of fuel systems. By eliminating the deadhead-style fuel rails and converting them to full-flow, any air that finds its way in through fuel bubbles or pump cavitation can take the path of least resistance and pass through the heads and flow out the Aeromotive regulator return port to the tank, instead of exiting through the fuel injectors.
So, more than just preventing air intrusion, the CPR system actually works to constantly purge air and can do so with just a twist of the key. That's particularly handy if you happen to run out of fuel (we've all done it), or when cracking the seal on the system to change injectors or the fuel filter. This also directly addresses the common fuel starvation of injector #8 (it's typically the loudest injector) and ensures that each fuel injector has adequate and equal fuel quantity and pressure at all times.
As for filtration and flow, they're actually symbiotic. Through testing, DieselSite's resident 7.3L guru Bob Riley found that fuel delivered through the OEM fuel filter in stock form flows roughly 4 to 6 gph. Once converted to a CPR regulated-return-style system, however, the same pump delivered fuel through the OEM fuel filter at about 24 gph. That's great news for eliminating fuel starvation issues for hard-working or hot-rodded engines, but that rate is also far above what the stock filter was ever intended to see. To address that concern and add increased protection for the pump itself, Bob tested dozens of filters until he found one that could handle the high flow rate while filtering to at least OEM requirements. Actually, the CPR's pre-pump filter is rated for double the expected flow rate while filtering down to 2 microns-much better than OEM. At this point, the OEM filter basically becomes a redundant safety feature in case the pump itself comes apart.
And if all that's not enough, for 7.3L trucks, this is one of the foundation mods that should be on the list for anyone seeking bigger and badder parts, since it will increase the effectiveness of everything from larger injectors to custom tuning. As a matter of fact, we're of the opinion that a good fuel system that addresses the factory shortcomings should be high on the priority list, otherwise you'll just find yourself playing catch-up to compensate.
Bob routinely sees at least 10 to 40 hp from the upgrade, thanks to the vastly improved fuel flow, but it's mostly on the top end. Other than faster cranking, unless your fuel system was in poor enough condition to cause hesitation or high aeration, it'll still feel essentially the same during daily driving.
Notice we said "feel" in that last statement, that's because it certainly won't sound the same. While we did notice faster cranking and slightly better pull under full-throttle, the thing that really blew us away is how much quieter and smoother the engine runs. And we don't mean by a little bit-it's like a completely different engine.
At cruising rpm on the freeway under light-throttle, we actually had to turn the radio completely off to even hear it. No joke, it's that quiet. The stereotypical 7.3L clatter and clanging were dramatically lessened, proving that they are mostly attributable to poor fueling. With the pedal to the floor, we also heard more turbo than engine and felt significantly less nosing over near redline thanks to each injector getting the exact fuel and pressure it needed. It still sounds like a diesel without a doubt; it just sounds like a smoother, more modern, and refined one-something we never expected to achieve with our archaic 7.3L.


Crystal River, FL 34429


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