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Method of Controlling Common Rail Fuel Injection Device

Common Rail SystemsUNDERSTANDING TYPICAL PROBLEMS OF COMMON RAIL FUEL SYSTEMS INHERENT PROBLEMS

1/19/2018 11:41 AM  | Author: Cindy

Given the complexity of the steps involved, several areas can be prone to failure, but often due to a single simple problem: contaminants. As Todd Emmert, machine shop manager for Scheid Diesel, points out, the problem usually boils down to three key words: “Fuel, fuel and fuel.” He’s not kidding here. Aside from debris and particulates, “There’s too much emulsified water in it.”

In other words, that gold tint you might see on fuel components doesn’t glitter. It’s actually a film or residue (what gasoline guys sometimes call “shellac” or “varnish” on a carb) created by corrosion from too much moisture. What this does to an injector is erode the injector’s valve seat in the control valve assembly, degrading the precise flow of fuel. It’s a critical component, since common rail systems have much higher injection pressures, and tolerances are measured out to five-place decimals. This minute thickness makes a human hair look like a tree trunk by comparison.

In the valve assembly, fuel passes through a tiny orifice at very high pressures. The opening is sealed by a check ball only 1mm in diameter. Contamination from water and debris have an abrasive effect on the orifice, grinding the surface, which quickly and inevitably leads to a poor seal between the valve and the check ball. This in turn results in poor injector performance including starting issues, reduced fuel economy and performance, and rough running.

The presence of water also impedes lubricity, resulting in metal-on-metal contact, Emmert observes. Where does the moisture come from? He says that biodiesel is a typical component of most No. 2 diesel (whether it’s labeled as such or not) and it tends to attract water droplets. But moisture can also come from condensation of outside air, leaky storage tanks at a fuel station, or even rainwater puddling on top of an auxiliary tank in the bed of a pickup.

Sometimes the HP pump is mistaken as the cause of hot starting, low-power (or no-power) conditions. To avoid any unnecessary repairs, the first thing Scheid’s shop technician Daryn Clapp does is check for diagnostic trouble codes (DTC). The injection balance rate will indicate low compression in a cylinder by displaying the crank-speed values on the downstroke of the piston.

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