Diesel fuel systems require precise fuel sprays for reliable, consistent combustion — that’s where injector systems come in. These high-pressure systems send regular fuel streams to the engine to keep your vehicle running.
The hydraulic electronic unit injector (HEUI) system is a computer-controlled system with a combined high-pressure pump and injector for each engine cylinder. It replaced traditional mechanical injection using high-pressure engine oil and electronic controls to manage fuel delivery, allowing for more precise timing and better performance. Today, HEUI technology is being phased out in favor of high-pressure common rail systems. However, HEUI systems are common in the 7.3L and 6.0 L Powerstroke engines used in Ford trucks.
What Are HEUI Fuel Injectors?
Caterpillar and Navistar developed the HEUI fuel system in the early 1990s. It was a major advancement in diesel engine design because, unlike traditional mechanical injection systems, HEUI uses high-pressure engine oil to actuate injectors, allowing for independent control of fuel timing and pressure through electronic signals. This feature greatly improved fuel atomization, combustion efficiency and emissions control. These elements form a tightly integrated HEUI system:
- HEUI injectors: These components rely on high-pressure oil to deliver fuel to the cylinders.
- High-pressure oil pump: The HEUI pump supplies oil under intense pressure.
- Powertrain control module (PCM): The PCM works in tandem with sensors to act as your engine control system’s brain.
- Injection control pressure (ICP) and injector driver module (IDM) sensors: The ICP and IDM sensors work with the PCM to monitor engine conditions and control injection timing and volume.
How Does the HEUI System Work?
The HEUI fuel injection system uses its components to achieve optimal performance:
- The PCM sends a signal to begin fuel injection based on engine conditions.
- The high-pressure oil pump supplies pressurized engine oil to the injector.
- The oil pushes a piston or intensifier inside the injectors, pressuring the fuel below it.
- The high-pressure fuel is forced through the injector nozzle and sprayed into the combustion chamber.
- The PCM electronically controls injection timing and duration, allowing precise fuel delivery.
- Once the injection is complete, the oil and fuel reset for the next cycle.
Common Rail vs. HEUI Injector Systems
With a common rail injector system, one line — or rail — of pressurized fuel feeds multiple injectors, which all fire at different times. A high-pressure pump supplies up to 35,000 pounds of pressure to the line. The computer then determines the amount of fuel to spray and the timing. Each injector can spray up to five finely atomized strokes per combustion cycle.
This kind of system controls two pilot sprays, one main spray and two post sprays, which means that in addition to the pre-top dead center (TDC) injection, the common rail system may pulse another four times during the downward pass of the piston. These extra sprays provide more torque than a HEUI or mechanical system can. With the proper air intake, the common rail system provides a more efficient burn with nearly 100% ignition.
Piezoelectricity in Injectors
Some newer common rail systems, like the Powerstroke 6.4L and 6.7L, use piezoelectricity, enabling them to function at a higher speed than HEUI or mechanical systems. The term “piezoelectricity,” which literally translates to “pressing electricity,” refers to the electricity passing through crystals under high amounts of pressure.
You’ve seen piezoelectricity in action if you’ve ever seen someone crunching on hard candy in the dark. Crushing the sugar crystals in the candy releases the energy within them, producing electric sparks. A similar thing occurs in fuel injectors, but the crystals remain intact, so they vibrate back and forth, allowing the electrical current to flow through them.
Piezoelectric common-rail injectors are also quieter than their HEUI predecessors, with increased horsepower and torque.
How to Maintain HEUI Injector Systems
As diesel injector technology advanced, so did its demands. Modern injectors have tighter tolerances and rely heavily on clean, high-lubricity fuel. Unfortunately, many fueling stations deliver low-lubricity diesel, which is contaminated with water, dirt, or other contaminants. This low-quality diesel poses a serious risk of clogged filters, poor performance and total injector failure.
Diesel naturally contains lubricating compounds, but the EPA-mandated reduction in sulfur through hydro-processing removes many of them, resulting in drier, less protective fuel. That’s why regular maintenance is critical. Changing your fuel filter and using high-quality fuel additives helps restore lubricity, protect injectors and extend system life.
Tips for HEUI Injector Maintenance
- Fill up with quality fuel and oil: Avoid clogging injectors and damaging pumps with high-quality, clean fuel and oil. They protect your entire system from premature wear.
- Stick to regular oil changes: Dirty or degraded oil affects the HEUI system’s hydraulic performance since it uses engine oil to actuate injectors. Clean oil ensures consistent injection pressure and timing.
- Check sensors regularly: Sensors like the ICP and IPR are system-critical, so check them to ensure proper functioning to avoid hard starts, rough idling and injector failure.
- Use fuel additives: Every time you fill up, include an additive like Hot Shot’s Secret Everyday Diesel Treatment to ensure lubricity, clean injector tips and prevent internal wear. This additive will help your injectors and fuel system last longer and run more efficiently.
Common HEUI System Issues and Solutions
Here are some of the prevalent HEUI system problems and fixes:
- Injector failure: Worn or clogged injectors can cause misfires, rough idle or poor economy. Use Hot Shot’s Secret Stiction Eliminator to clean and protect injectors — it has saved thousands of failing injectors.
- High-pressure oil leaks: Leaks in the oil rail, standpipes or seals can cause hard or non-starts. Inspect and reseal the high-pressure oil system and replace damaged O-rings.
- ICP sensor issues: A failing sensor can disrupt pressure readings and cause rough performance. Test the sensor with a scan tool and replace it if readings are erratic or out of spec.
- Sticking IPR valve: A faulty IPR valve can cause stalling, power loss or starting issues. Remove, clean or replace the IPR valve and inspect the IPR screen for debris. Replace it if it is clogged.
- Dirty or degraded oil: Old or contaminated oil causes injector stiction and poor injection timing. Perform regular oil changes using high-quality oil to limit buildup and improve performance.
Hot Shot’s Secret Solutions for HEUI Injectors
Hot Shot’s Secret formulates trusted products to keep your HEUI system running at its prime:
- Diesel Extreme: Trust this deep-cleaning fuel additive to clear out injector deposits, remove water and boost cetane for better combustion.
- Everyday Diesel Treatment: Use this powerful additive with every fill-up to protect your entire fuel system.
- Stiction Eliminator: Keep HEUI injectors clean and restore failed units with this highly effective oil treatment.
Safeguard Your Injectors With Hot Shot’s Secret Products
Give your diesel engine the best care from Hot Shot’s Secret! With our fuel additives, you can boost injector life and enhance performance. Explore our full range of proven products to keep your HEUI injectors clean and efficient.