Hydraulically-actuated, Electronically-controlled Unit Injectors (or HEUI injectors for short) will have a tremendous impact for the good, or not so good, for the foreseeable future.
PowerStroke diesel and Caterpillar powered RV vehicles depend on HEUI systems to deliver the fuel and make these engines run. The HEUI design uses a second high-pressure oil pump and delivers a constant flow of very high-pressure motor oil to gallery passages in each cylinder head. (Pressures between 500 and 3000 psi) When the electric solenoid on top of a HEUI injector is actuated, this high pressure oil is directed into a chamber inside the injector and provides the hydraulic pressure to force an intensifier piston to move downward. The intensifier piston in turn pushes fuel out into the cylinder. Fuel is injected into the cylinder at pressures as high as 21,000 pounds per square inch.
The technology described here is really quite amazing. It permits fuel control that is so precise that, combined with the rest of the system, cylinder performance can be monitored and instructions to each injector modified to make a smooth running engine even when other mechanical factors would make other engines run rough.
Priced in the neighborhood of $300 per injector, a set of 8 injectors along with the labor to change them can cost more than we used to pay for a complete engine 15 years ago. These injectors depend totally on clean oil of high quality, clean fuel and fuel with enough lubrication ability to make pumps and nozzles have a long, dependable service life.
PowerStroke engines pump unfiltered oil from the sump to the high-pressure oil pump and then to the injectors. This means that to not change oil or to do anything that contributes to accumulation of dirt in the engine will subject your expensive injectors to wear and potential damage as particles suspended in the oil get forced into the injectors.
Because the injection system uses unfiltered oil directly from the pan , it makes total sense to use the very best synthetic motor oil after break-in. High quality synthetic lubricants can tolerate much higher temperatures without coking or breaking down. The best synthetic oils also keep the engine clean by being able to dissolve deposits and keep them safely in suspension to be filtered out or removed at drain time. It is a good idea to install a bypass oil filter on these engines. A fine bypass filter slowly filters the oil to remove particles as small as 2 microns. The full flow filter lets particles below 20 to 30 microns stay in the oil. It is the particles between 5 and 30 microns that are responsible for most of the wear on HEUI injectors and engines. Adding bypass oil filtration, in addition to the normal full flow oil filter, will get rid of these small particles, which would otherwise accumulate in the motor oil to become the cause of wear and failures.
Oil is important to HEUI systems but fuel is equally important. The lower section of a HEUI injector is lubricated by fuel. Dirty fuel means injector wear. Changes in our fuel to help the environment have resulted in the fuel we buy being a poor lubricant compared to the fuel of 10 years ago. You need to use a top quality fuel additive in every tank of fuel if you want to get the best life out of your HEUI fuel system components. You also need to stay on top of fuel filter maintenance. Make very sure to use only filters from Raycor, Parker, Ford or Navistar, as there are inferior filters available that suffer from torn seals and let dirt into your injection system.
Another fact about HEUI injectors is that they rely on o-rings to keep fuel and oil from mixing or escaping from their proper flow paths and causing performance problems or engine damage. HEUI injectors use 5 o-rings. The 3 external ones have been the subject of a great deal of trouble and do need to be replaced with updated o-rings if they fail. The 2 internal o-rings are not field replaceable. If these fail then the injector or injectors must be replaced. While HEUI systems are inherently reliable if properly maintained they present some diagnostic challenges when injector hydraulics are not working properly. It is often possible to tell which head has a pressure leak but the only way to prove the cause of the leak is a process of elimination. You can change the external o-rings and see if this fixes the symptom. If external o-rings do not fix the symptom then you either have an internal o-ring problem or a leak in the head itself, like a casting crack. You prove which cause is at fault by replacing the injectors in question. If this doesn’t fix the symptom then you have a bad head or heads.
The most common symptoms of injector o-ring trouble are oil getting in the fuel, the fuel filter element turning black, long cranking times before starting, sluggish performance and reduction in power. Increased oil consumption often accompanies oring problems or any fault that lets fuel in the oil.
Any money that was saved by ignoring or neglecting needed maintenance on lower mileage vehicles comes no where near being worth the pain of parting with thousands of dollars for fuel system repairs that could have been avoided.