An article has circulated on the internet titled ‘Not Common Rail alone. What on Bosch, Delphi, Denso or Siemens is not like Caterpillar and what ruins it”, where they told about how injectors with HEUI system developed by Caterpillar differ from diesel injectors of other brands, by what reasons these injectors break down and how they are repaired.
Caterpillar’s official dealer – made a comment, to quote from the article:
“Caterpillar itself rebuilds the injectors, but states that non-factory repairs to HEUI are not possible. And because Caterpillar has such a policy, original HEUI repair parts are not available, or in other words, are unavailable to third party repairers” – circulating on the internet and social media.
“This statement is not entirely accurate and may, without an explanation of the reasons for this policy on the part of Caterpillar, form a misconception on the part of the audience of readers of online resources” – Caterpillar’s spokesperson said.
We would like to clarify the logic behind this Caterpillar position.
Caterpillar recommends that certain components (including the HEUI fuel system parts with fuel injectors used on Caterpillar 3126B, 3126E, C7, C9 engines such as the HEP hydraulic pump, HEUI pump injectors) be repaired by Caterpillar in specially designed specialized plants which repair only these types of components. Caterpillar has such a plant in Mexico.
These specialised plants are equipped by their nature with a wide range of unique, highly specialised technological equipment which allows high-quality diagnosis and repair of these components, bringing them to the condition of new ones. Components repaired in specialised plants are labelled REMAN (from the word Remanufacturing). The factory guarantees the same guarantee as for new spare parts and is equal to 12 (twelve) months without any operating time limitation.
Returning to the CAT HEUI fuel system injectors, the final repair cycle at the factory, after completing the mechanical part of the work itself (disassembly, defectology, selection of defective parts and identification of those suitable for repair, replacement of defective parts, assembly) includes a run-in on a special alignment bench. The bench enables accurate determination of the actual cyclic delivery rate of each particular injector and provides information on the necessary correction of the signal sent by the electronic control unit to the injector at each operating cycle (TRIM File).
This TRIM File is written to an optical data carrier (CD) and is supplied with a new or repaired injector (REMAN). When installing new or repaired injectors in the engine to replace a defective injector, it is imperative that the correction data (TRIM File) be entered in the Engine ECM.
This ensures equal cyclic delivery of all injectors of the engine (uniformity of engine operation), achievement of the declared characteristics of power, environmental performance, preservation of the engine oil and piston parts (pistons, valves) life declared by the manufacturer.
In Caterpillar diesel engines with the HEUI fuel system, cycle rate control is achieved by varying the opening and closing times of the shut-off valve and by varying the time the shut-off valve is open.
The control signal is applied to the control solenoid for a strictly defined period of time in relation to the current crankshaft position. The duration of the signal determines the amount of fuel to be delivered to the combustion chamber.
Based on the conditions described, it is necessary for each individual plunger pair to deliver a strictly identical amount of fuel at the same duration of the control signal and therefore other equal parameters. The accuracy of the fuel system however, is not yet able to cope with the required variation of the individual pump injectors.
As a result, with the same signal duration, every pair of plungers produces a different quantity of fuel.
The fuel delivery phases may also differ due to the different actuation speeds of the drive mechanisms. The pressure in the oil line to the injectors is a constant for each individual engine condition.
Thus, the only available way to equalise the cyclic delivery performance of the HEUI pump injectors is to change the start and end torque of the control signal, which is achieved using TRIM File software, a parameter that is written into the engine electronic control unit.
In the final stage of the manufacturing (repair) process, the individual operating characteristics of each pump injector are determined individually in a final test run. Using these data, a software correction to the unit’s operating parameters is determined. The correction is a numerical value of how far the flow rate and response time of the sample differ from the reference.
The control unit, with information about the numerical value of the correction, is programmed to change the torque of the control current to the solenoid and its duration. The result is that the cylinder-by-cylinder fuel supply is averaged.
In view of the above, we would like to point out that this unit is complex to build and equally complex to repair. As of now, we have no information that any repair organisation other than the CAT repair plant itself carries out the complete repair cycle, including the final, important stage of generating a TRIM File for each individual pump injector that has been repaired.
In its turn, installation of pump injectors, repaired only mechanically, in engines with already saved TRIM-files for parameters of absolutely different injectors, installed earlier from the factory or at replacement by dealer’s service technicians, is fraught with problems with smoke, soot formation, local increase of combustion temperature in cylinders (resulting in burnt pistons, valves), loss of power, etc.
A further argument in favour of carrying out a comprehensive diagnosis of this type of fuel system is the fact that there is another hydraulic component in the circuit that directly affects the performance of the pump injectors. This is the HEP (High Efficiency Pump) hydraulic pump, whose main task is to create the necessary drive pressure (variable depending on the engine operation mode) for the pump injectors.
The HEP is a variable displacement axial piston pump regulated via an electro-hydraulic valve controlled by a signal from the engine ECM. As a component that has electrical (control solenoid), electronic (pressure sensor) and mechanical (the axial piston pump itself) parts, it needs a comprehensive check of all these parts during diagnosis, as a malfunction of any of them will have a significant impact on the performance of the system as a whole.
Specialized diagnostic tool from Caterpilar (CAT Electronic Technician) that is used by technicians of authorized dealerships, allows you to conduct a series of tests and determine the correctness of HEP pump and pump injectors, that is, to determine the most likely causes of failure before the components are dismantled from the engine.
We hope the above will give you a better understanding of the structure, design and benefits of this type of fuel system diagnosis and repair in an authorised Caterpillar dealership and specialised repair facility (CAT REMAN programme)”.
