5 Ways to Ensure a Common-Rail Fuel System’s Longevity
Sorry, 12-valve fans. Fueling makes a big difference in performance.
"Common rail." It is a term that at this point is universally known across the entire diesel space. However, for uninitiated or new enthusiasts, the term refers to the manner in which late-model/newer diesels are fueled; via an injection system that is founded on a high-pressure pump that supplies fuel to independent rails (single rail for I-4 and I-6 engines, or a pair for V-8s), which then feed each injector individually.
Contrary to popular thought, while the term arguably became a global descriptor (kind of like the way we use "Kleenex" when talking about any tissue brand), with the advent of Cummins' electronically fueled 5.9L engines of the late 1980s, "common rail" is not exclusive to Clessie's finest.
Ford's Power Stroke and GM's Duramax engines are similarly fueled. However, we acknowledge that in today's popular jargon, referring to a diesel pickup truck simply as a "common rail" typically means it's a Dodge Ram or Ram that has a 24-valve 5.9L or 6.7L Cummins engine under its hood.
In this report, we're keeping things broadband and addressing common-rail fueling without any brand alliance. We have touched on CP3 and CP4 injection pumps in other editorials (highlighting their role in improving a diesel engine's performance), and the importance of protecting those parts from damage due to contamination, excessive pressure, etc. Now we're addressing how—when manipulating fuel to increase power—you can ensure a fuel system sustains, by following these five great tips provided by our friends at NW Fuel Injection Service in Surrey, British Columbia.
Most Cummins fans (especially the OGs) know that early Bosch fuel pumps (VE, and P7100) can be tricked into increasing injection pressure by restricting the flow of fuel returning to the tank. While those pumps support this type of modification, it won't work with common-rail systems.
Restricting the flow of a CP3 or CP4 pump will build up excessive pressure in the housing; enough to blow driveshaft seals and inspection plugs out of the pump. A high-pressure injection pump depends heavily on the fuel-return line to relieve the excess pressure that is built up inside the pump and send it back to the tank.
When you're checking a truck's fuel system, again, do not restrict the return line. Also, in certain instances (with modified CP3 pumps) you will actually need to increase the size of the return line to support the additional flow.
With common-rail fueling, more inlet (feed) pressure is not always better, as too much can create the same type of problems as restricting the return line cause. A multiplication effect takes place; if fuel enters the pump at too high a pressure, it will develop tremendous pressure (up to 40,000 psi) inside the pump and burst seals, damage the pump internally, or hurt the injectors. For high-performance applications, NW Fuel Injector Service recommends using a pressure gauge on the feed side to ensure there is correct fuel pressure at all times.
Here are recommended feed pressures for CP3- and CP4-equipped engines:
- Cummins 2003-2016 (5.9L and 6.7L): no less than 8 psi/no more than 15 psi
- Duramax 2001 2016 (6.6L): no less than 8 psi/no more than 10 psi
- Power Stroke 2011-2016 (6.7L): no less than 8 psi/no more than 10 psi
Condensation and Water Contamination
Diesel fuel absorbs water. And with this being the case, it is not a surprise that water contamination is the number one reason for diesel fuel system failures. For this reason, if a diesel truck is not going to be used for more than 30 days, fill up its fuel tanks completely to ensure the least amount of air space is available for condensation to collect. Also, change fuel filters more frequently if the vehicle sits around a lot.
Water (condensation) collects on the walls of the fuel tank creating little moisture droplets that form during the daily heating and cooling of the surrounding air. The greater the temperature differential, the faster the water collects. It usually takes about 28 to 30 days for condensation to form inside the fuel tank of a truck that's engine has not been started. This moisture accumulates in the fuel and begins to create rust and algae inside the tank, and ultimately contaminates all of the fuel system components. For extended periods of storage, we recommend using a diesel fuel additive that contains a stabilizer component, and a mild biocide to extend the life of stored fuel and inhibit algae growth.
No additives can eliminate water from diesel fuel (alcohol-based products or methyl-hydrate products are not for use in diesel fuel). With this being the case, the first line of defense on an oil burner is a water-separating fuel filter. Change fuel filters at every other (second) oil-service interval.
Diagnose With Stock ECM Calibration
Before performing common-rail fuel system diagnostics on a truck with an engine that is custom tuned, we suggest returning the ECM calibration to stock. Why? Because doing so can improve the accuracy and speed of the analysis. Custom tunes can mask problems and make failing components less obvious and correctly diagnosing the actual problem more difficult.
When the ECM tuning is returned to stock, the OEM test values and diagnostic-check procedures and specifications will more accurately reflect what is happening, to help pinpoint the source of a problem more quickly.
NW Fuel Injection Service