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Mechanical, HEUI, And Common-Rail Injectors - Basic Training

Your Diesel Injector Tutorial

Mike McGlothlin
Mar 13, 2014
Photographers: Courtesy of the Diesel Power Archives
Ever wondered which injectors are in your truck, what they look like, or even how they work? Throughout the progression of diesel injection systems, this component has gone from extremely simple to highly complicated and advanced. The reason? With horsepower goals to meet and emissions regulations to adhere to, engine manufacturers are always looking to use the latest and greatest injector technology available. Below, we’ve illustrated each type of injector you’ll come across in the diesel pickup realm, from the mechanical ones found in your 12-valve Cummins to today’s piezo-electronic units in your quiet common-rail.
Mechanical Injectors
Found On: ’82 to ’98 GM 6.5L IDI, ’83 to ’94 Navistar 6.9L and 7.3L IDI, ’89 to ’98 Cummins 5.9L 12-valve, ’98½ to ’02 Cummins 5.9L 24-valve
12-valve Cummins
The simplest injector found in a diesel engine is a completely mechanical unit. With very few moving parts, this is all you’ll see inside a Bosch unit off a 12-valve Cummins. Totally free of any computer telling it what to do, this injector fires (pops off) according to pressure it’s been supplied from the injection pump. Once the pressure within the body is high enough, the check valve lifts off its seat, allowing fuel to spray through the nozzle, out the tip, and into the cylinder (or the pre-chamber on the GM and Navistar IDI diesel engines listed above). Leftover fuel is returned through the injector body back to the injection pump.
Photo 2/7   |   12 Valve Cummins Fuel Injector
24-valve Cummins
Similar to the 12-valve Cummins’ injector is the ’98½ to ’02 unit found in the 24-valve mill. There is nothing sophisticated about the injector itself, and other than the stepped nozzle holder, it’s almost identical to the 12-valve injector. The electronic portion of the ’98½ to ’02 fuel system lies in the VP44 injection pump, which, unlike the earlier P7100, can vary the timing and fuel delivery according to an ECU. While primitive in design, mechanical injectors benefit from simple operation (such as single-shot injection events), greater affordability, and better reliability than newer, common-rail injectors, with their mechanical internals known to last at least 200,000 miles.
Photo 3/7   |   24 Valve Cummins Fuel Injector
HEUI Injectors
Found On: ’94½ to ’03 7.3L Power Stroke, ’03 to ’07 6.0L Power Stroke
7.3L Power Stroke
Hydraulically activated, electronically controlled, unit Injectors (HEUI) debuted in the Caterpillar-designed HEUI injection system found on Navistar-built 7.3L Power Stroke V-8s. The system relies on highly pressurized crankcase oil (instead of diesel fuel) to fire the fuel side of the injectors. Once oil leaves the high-pressure oil pump, it makes its way to the injectors via the oil rails within each cylinder head. From there, oil that has been pressurized as high as 3,000 psi in 7.3Ls, and 3,600 psi in 6.0L engines, is allowed to enter the injector through the poppet valve (called a spool valve in the 6.0L’s case) once the injector solenoid is commanded to open it via a computer module.
Photo 4/7   |   7 3l Power Stroke Fuel Injector
6.0L Power Stroke
In a chain reaction of events, the pressurized oil then pushes down on an intensifier piston, which forces the plunger on the fuel side downward, thereby forcing the nozzle needle to lift off its seat, spraying fuel into the cylinder. Fuel supply makes its way through a fuel inlet in the bottom half (fuel side) of the injector thanks to either a mechanical lift pump in the valley (’94½ to ’97 7.3L) or an electronic unit mounted along the framerail (’99 to ’03 7.3L and ’03 to ’07 6.0L). Fuel supply pressure is higher than in engines utilizing conventional injection systems and ranges from 45 to 65 psi.
Photo 5/7   |   6 0 L Power Stroke Fuel Injector
Common-Rail Injectors
Found On: ’01 to current 6.6L Duramax, ’03 to ’07 5.9L Cummins, ’07½ to current 6.7L Cummins, ’08 to ’10 6.4L Power Stroke, ’11 to current 6.7L Power Stroke
LB7 Duramax
The common-rail injection system was introduced in 1997, but GM was the first of The Big Three to implement it on one of its engines for the ’01 LB7 Duramax. In 2003, the 5.9L Cummins followed suit, and even the new 3.0L VM Motori V-6 in the ’14 Ram 1500 and Grand Cherokee uses them. The solenoid valve-equipped common-rail injector (activated by the engine’s computer) controls fuel quantity and timing, rather than the injection pump, and it draws stored fuel from the rail(s) as needed. Multiple, precise injection events allow this style of injector to outperform its mechanical predecessors in terms of noise, where pilot injection events precede the main event to quiet diesel clatter. For improved emissions, 26,000 to 30,000 psi injection pressures and post injection events are used for a cleaner burn. Their drawbacks include added complexity, cost, and tighter tolerances—making them very intolerant of contaminated fuel.
Photo 6/7   |   Lb7 Duramax Fuel Injector
6.4L Power Stroke
In 2007, Ford introduced its ’08 6.4L Power Stroke with piezo-electric common-rail injectors, which is currently the most advanced injector you’ll find. Ultra-quick injection events are made possible thanks to their use of piezoelectricity, which employs crystals and electricity as an actuator to open and close the injector. In the 6.4L’s case, five injection events occur per combustion cycle (two pilots, one main, and two post events). Engines equipped with piezo injectors are arguably the quietest diesels you’ll hear. In addition, this style injector is capable of mega horsepower with aftermarket tuning involved. Piezo injectors are also used in Ford’s 6.7L Power Stroke and GM’s ’11 to present LML Duramax, and will be utilized in the Nissan Titan–destined 5.0L V-8 from Cummins.
Photo 7/7   |   6 4l Power Stroke Fuel Injector

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