A tuning technique long shrouded in mystery, ROM tuning has been used by the Japanese tuning industry since the late '80s. Not until recently, though, did ROM tuning begin to take off in America. Most tuners would opt for either a piggyback system (Power Enterprise Cam-Con, SDS- Simply Digital System, A'PEXi SAFC) or go with a stand-alone-type system (A'PEXi, PowerFC, HKS VPro, Motec). With the introduction of factory ECUs with flash capability and the development of cost-effective tuning software, ROM tuning is quickly becoming a popular tuning solution. We turned to longtime ROM tuner Kazuhiro Fujioka of Auto Produce Boss to shed some light on why ROM tuning has been the primary choice for many tuners in Japan.
Kazuhiro says that with a base knowledge of ROM tuning, stand-alone tuning becomes much easier.
What is ROM tuning anyway? Essentially, it's manipulating the factory data within the stock ECU's programming to optimize engine performance after the addition of aftermarket parts. Data within the factory ECU is changed to work with increased airflow and injection. The tuner is basically doing the same thing that would be done with a stand-alone type system, except it is all within the factory ECU. Sounds easy enough, right? The problem lies in knowing where the data sits within the programming of the ECU and how to access it. The data and operating machine language all lies in a chip within the ECU. This chip has to be read to ana- lyze the data and figure out what string of data controls what. Once you have this, the data can then be manipulated for whatever purpose needed. Kazuhiro explains that in the past this data would be dumped into a file and analyzed on software like Techtom's Mighty Map.
Mighty Map gives you the capability of reading and writing a file, but it doesn't tell you where the data lies within the file itself.
Tuning is done on the bench instead of in real time. This also involves an investment in base equipment. Besides the need of the obvious air/fuel meter and scanner, the tuner would also have to invest in software as well as addressing and soldering equipment in order to be able to properly tune a car. On top of that, tuning is done in hexadecimal format. Mighty Map doesn't lay the data out for you in a graphical fashion; it is in its raw format. This means that you have to understand what the code means to be able to manipulate it.
The main chip with the JECS written on it is where the data is for the ECU.
More recently, car manufacturers have utilized flash technology in their ECUs. This means that the base data can be rewritten a finite amount of times onto the chips via either the OBD port or directly attaching a cable to the ECU itself. This has made ROM tuning much more accessible than before. Software is in development for older makes to incorporate emulator technology and allow tuning real time. On top of that, software is readily available through the Internet and users can share data.
Continuing to become more and more sophisticated, the piggyback system is still limited in control as it manipulates the airflow signal to trick the ECU into thinking it is at a lower or higher amount.