HEUI Injector Repair


At DFIS we test your HEUI injectors to make sure they meet manufactures and Alliant specifications. Once a set of HEUI have arrived for testing a trained service technician will flush out your HEUI and remove any carbon build up from the nozzle tip. Once this has been complete the technician will install then in to the HI 2000 test stand and run then through a six step test procedure. The results from these test’s will be compared to manufactures and Alliant specifications to determine the status of your injectors. If they meet specifications and are “good to go” we will re o-ring them and get them back to your mechanic for instillation.


HEUI Facts

The operation of the HEUI fuel system is different from mechanically actuated fuel injection systems. The HEUI fuel system requires no mechanical adjustment. Installing different software in the ECM makes changes in performance. The engine uses an HEUI in each cylinder. A solenoid on each injector controls the amount of fuel delivered by the injector. An engine speed/timing sensor detects top dead center (TDC). All fuel injection is timed off the occurrence of TDC. The ECM determines how much fuel is to be delivered based on the difference between desired and actual speed. The ECM then sets the timing from TDC for each cylinder based on data received from the coolant temperature sensor, inlet air manifold temperature, atmospheric pressure sensor, and turbocharger outlet (boost) pressure sensor. The ECM adjusts timing and fuel delivery for best engine performance, fuel economy, and white smoke control. The HEUI fuel system uses a hydraulically actuated electronically controlled unit injector. All fuel systems for diesel engines use a plunger and barrel to pump fuel under high pressure into the combustion chamber. Fuel is pumped into the combustion chamber in precise amounts to control engine performance. The HEUI uses engine oil under high pressure to power the plunger rather than a fuel injection pump camshaft lobe to power the plunger. The HEUI uses engine lubrication oil that is pressurized from 870 psi (6 Mpa) to 3500 psi (24 Mpa) to pump fuel from the injector. The HEUI operates in the same way as a hydraulic cylinder to multiply the force of the high- pressure oil. By multiplying the force of the high-pressure oil, the HEUI produces injection pressures that are very high. This multiplication of pressure is achieved by applying the force of high-pressure oil to a piston. The piston is larger than the plunger by approximately six times. The piston pushes on the plunger. The engine lubrication oil under high pressure is called the actuation pressure of the oil. The actuation pressure of the oil generates the injection pressure delivered by the unit injector, increasing the pressure by a factor of six. Low actuation pressures result in low injection pressure of the fuel. During conditions of low speed such as idle and start, low injection pressure is used. High actuation pressure during high idle and acceleration results in high injection pressure of the fuel. The HEUI fuel system provides infinite control of injection pressure.