Differences Between HEUI Injectors and Non-HEUI

April 10, 2019

Injector design has been conveyed across three primary design concepts. The mechanical based system was a system based on injector pressure and mechanical release. The 2-phase system simply allowed the activation of the injection pump to build pressure within the injector to then lift the check valve and open the flow of pressurized fuel to spray.

The High-pressure Electronic Unit Injection (HEUI) system followed as one of the first designs helping revolutionize the clean-burn, quiet diesel engine. Opposed to the prior single-shot fuel injection design, HEUI systems use an electronically controlled hydraulic activation with a high-pressure oil pump forcing a plunger within the injector to open the needle to fuel spray into the combustion chamber.

With the addition of electronic control, the HEUI system enhanced accuracy in injector cycles. The entire stroke cycle is controlled by the fuel system computer, with a much more accurate timing for injection and fuel metering with a higher injection pressure over the previous 2-stage injection design.

And with a common rail injector system, multiple injectors can fire at various stages all fed by a common line of pressurized fuel.

Shane Matt of L and M Fuel Injection Service Inc. (Lafayette, LA) says, “the inclusion of computers enable the injector to spray more than once per combustion cycle. In the old style diesel, all of the fuel was mechanically injected on top of the piston, right before top-dead-center (TDC) on the crankshaft, to coincide with the optimal heat buildup from the compression.”

“Nowadays,” says Matt, “just before that peak heat of compression build-up, just before TDC, injectors spray a pilot injection stroke with a minute amount of fuel. Once the crankshaft passes top-dead-center, the rest of the fuel is injected so that the torque is pushing the piston down after TDC, with nothing but power in downward force. Opposed to hitting all the fuel before TDC, and the need to still pass over top on the full spray, the ignition is fed just before, ‘assisting’ in the pass over TDC with optimal force remaining, to burn on the downside of the crankshaft.”

Matt claims the system provides much more torque and a quieter engine because you don’t have one big bang before TDC. “It’s a much smoother and much more efficient burn of the fuel process. The full combustion is no longer wasted on the upward stroke of the piston. The majority of the combustion takes place in the downward stroke and therefore the extra torque.”

And just as the mechanical pressurization system was replaced by the HEUI, the hydraulic unit injector typically found in the older 7.3L/6.0L Power Stroke engines and the DT466E Internationals, is now being phased out for the common rail injection system.

The newer systems utilize each injector as a spray nozzle with a constant supply of high pressured fuel supplied to the injector at all times, through a common rail of fuel. With all the injectors attached to a single rail, a high-pressure pump supplies up to 35,000 lbs. of pressure to the line. The computer then determines the amount of fuel to spray and the timing to do so. Each injector may spray various volumes of fuel, up to 5 strokes per combustion cycle. In addition to the pre-TDC injection, the common rail system may pulse another 4 times during the downward pass of the piston, providing increased torque over the HEUI system.

“You’ve got 35,000 pounds of fuel being sprayed out of these tiny orifices, just atomizing the fuel to almost a smoke, opposed to a mist,” says Matt. “With the proper air intake, the common rail system provides a much more efficient burn with nearly 100% ignition.”

By adding crystals to electric current, piezo electronics are now added to the common rail system controlling two pilot sprays, a main spray and two post sprays. Piezo-electric common-rail injectors are also quieter than their predecessors while increasing horsepower and torque.

As design specs, more sophisticated components and higher tolerances increase in the evolution of the injectors, so too does the intolerance of contaminated fuel. Shane says that most of the hazards to injectors that he’s sees in his repair service results from dirty fuel, water in the fuel, and fuel with a lack of lubrication.

“The diesel fuel system is totally lubricated by the fuel itself,” says Shane. “Government wants almost all the sulfur out of diesel fuel however, and the process they use to remove the sulfur from the fuel also removes lubricants. The hydrating process at the refinery creates a ‘dryer’ fuel more reminiscent of kerosene or jet fuel. Diesel engines are not designed for low lubricity fuel.

“Proper maintenance like changing your fuel filter, and additives, help avoid the premature wear of your fuel system,” advises Matt. “Neglecting the fuel filter can wreak havoc on a fuel system, and additives help increase lubricity, which really extends the life of fuel systems. For example, over the years, our customers that faithfully use Hot Shot’s Secret additives, their fuel systems are in pristine condition, after a longer than usual service life. We usually see them here with leaks instead of worn hard parts. On the other hand, we have those that use fuel straight from the pump without additives, and a lot of times they are in here earlier than they should be.”

“We have customers that claim added economy as well, just by using additives. When boosting the cetane, and the ‘burn-ability” of the fuel, you have more BTUs to work with, claims Shane. “Additives also have cleaning agents which helps keep your nozzle tips clean and functional. We have noticed a recognizable 25% increase in the longevity of the engine life with proper use of the additives.”


“I use Hot Shot’s Secret products in all my diesel equipment. Faithfully. It’s one of the key things now because you can’t get a fuel sample tested every time you tank up. You never know what you’re buying and you never know if the transport truck just dropped off a load that was severely hydro-treated and really low on lubricity. Why take the gamble; put a few pennies of additives in your tank and not only do you get the protection but also the peace of mind.

Hot Shot’s Secret Stiction Eliminator has repaired countless issues for customers of ours. In many cases, they come in for an injector replacement, but I have to be honest with my customers and pass along a good value. I sell them Stiction Eliminator instead of an injector and it very often solves the problem for a long time.

Stiction Eliminator has cured so many problems for our 6.0L Ford customers and they keep coming back.

In my own vehicle I had a lifter tapping. I put it in there and within a day or two of driving, the tapping went away. It just cleaned out the lifter to where they functioned normally again, and the engine was far quieter.

This stuff really works. I’ve got 5 vehicles plus 5 pieces of heavy equipment. I use Stiction Eliminator, FR3 Friction Reducer, Fuel Additives, very faithfully, on everything I’ve got.”

Shane Matt of L and M Fuel Injection Service Inc. in Lafayette, LA