Coding, Correction Code, Grading or Trims?
These are all common terminology used for generating a new code for a reconditioned injector. In essence coding, correction code and grading all refer to the same thing - an alphanumeric code which is assigned to an injector.
The alphanumeric code varies in length between different Fuel Injector (FI) manufacturers and different product families. The term trims however is the odd one out.
It’s possible that OE test methods may have over 400 measurement points to determine the performance characteristics of an injector, although from the 400 points there are really only a handful of critical measurements points, i.e. 16, which are used for generating a new code and these are known as trims. This refers to the performance offset or error at a critical measurement point against where the injector should be performing.
Workshop’s relationship with coding
Some workshops question the importance or relevance for coding on high, 100k mileage vehicle due to engine wear and tear. Many simply believe that that the ECU can automatically adjust the injector performance using closed loop control to bring the injector back to OEM standards during a “re-learn” period.
While this is technically true, this nonetheless misses the fundamental point of the need to validate if an injector is functioning back to OEM standards once refitted, or if it requires further adjustment.
Some workshops listen for engine “knock” at idle and fast idle, some will check the exhaust for coloured smoke, and others take the vehicle for a test drive to check for smoothness and power delivery.
Some will even use a diagnostic tool to check the level of fuel compensation at idle, (normally shown in % fuel trim). These methods provide a good indication of the presence of injector faults and incorrect coding.
However, because they are based on trial & error as well as being reliant on the experience of the mechanic, they are ultimately not a measurable way of proving a quality repair has been conducted, nor is this a wise use of a mechanic’s valuable time.
What does coding really add to what a workshop can do?
None of these methods do anything to confirm if the injector is performing back to OEM standards across the complete engine operating range, and more importantly, do not confirm complete and optimised combustion to ensure NOx and particulate matter is minimised to comply with the applicable emissions standard for that particular injector.
So is CR injector coding just a marketing gimmick to tell workshops they need to invest in another piece of equipment?
The answer from any serious player in the diesel industry is a resounding “No”. Coding is fundamentally the most important aspect of CR injector calibration because new and reconditioned injectors alike need to be re-aligned to deliver the correct quantity of fuel at the right time during the combustion stroke, to meet stringent emissions standards.
However, the coding itself is only as good as the quality and accuracy of the test to be able to assign the correct code in the first place. This is the second part of the story.
The effort to develop an All-Makes OEM quality coding solution requires a considerable amount of R&D activity. This is because each FI manufacturer uses different measurement strategies to determine the injector code definition and trim.
For Hartridge, the only sure way to determine each strategy is to perform a substantial amount of reverse engineering, utilising our extremely diligent R&D processes gained from our OE heritage and knowledge.
We recognise that any deviation from this process allows variables to be unaccounted for; a cardinal sin in the Hartridge engineering team!
However, most importantly it is imperative to perform on vehicle testing and use a process involving comprehensive data collection to reverse engineer the injector behaviours and fully understand the on-vehicle ECU drive logic and trim corrections.
What ‘proper’ coding looks like
One of the most unique injector manufacturer strategies is for Bosch Piezo injectors. Bosch performs a test known as “ISA”, which stands for Injector Learn Voltage. This test determines the required injector voltage to energise the piezo stack and deliver a pre-defined quantity of fuel.
This learned voltage is then translated into a single letter and is utilised as the last character within the final code. However that learned voltage is more than just a letter identifier, it also defines a voltage correction parameter for all the other test steps in the injector test.
Failure to apply this voltage correction parameter in the right way, or at all, will result in offset fuelling values and therefore incorrect codes being generated. This in turn has the potential to create incomplete combustion, high levels of NOx and particulate matter, even though the engine may seem to operate correctly!
Another great example is Denso G2/G3 coil injectors where it is absolutely mandatory to utilise forced air to cool the injector body during testing. Hartridge wanted to avoid using forced air cooling on the Sabre CRi to prevent additional service connections being needed for the machine.
However extensive R&D testing identified that it was impossible to achieve a consistent and repeatable result due to internal component separation due to overheating. The HJ088 air cooling kit, developed specifically for the Sabre CRi Master and Sabre CRi Expert, provides a significant advantage when coding Denso G2/G3 coil injectors as demonstrated in the graph.
Unfortunately, no other advanced injector control strategies could eliminate the requirement for forced air cooling, as the electrical coil energy is not affected by heat. Therefore this has resulted in forced air cooling across the injector body being the only viable option to provide a grading solution which mirrors OEM standards. When we say that we will take the correct path even if it isn’t the easy path this is what we mean.
However, not only is forced air cooling a requirement for Denso coding but also a closed loop test strategy is required with a varying number of test points depending on the application being tested to generate the required trim parameters. This can vary between 6 and 11 steps depending on the injector and how the Hartridge test plan has to be designed to enable on vehicle conditions.
One thing Hartridge can confirm is that if your test solution is not performing dedicated test steps and different measurement strategies for each FI manufacturer then you can be assured that your coding solution is not testing the injector to OEM quality standards and it could just be a marketing gimmick.
In a world where emissions standards are continuing to tighten and compliance testing becoming more prevalent, it will be the responsibility of the diesel industry as a whole to ensure it achieves best practice in the testing, repair and calibration of injectors.