Honda ECU codes are read in hexadecimal formula. Right now, you're probably wondering, "Heck-a-what!?" Programming in a Honda ECU is broken down into codes that put the challenge to electronics gurus while overwhelming the average enthusiast. Where most stand-alone units have fuel and timing maps broken down in to milliseconds on injector time and actual timing degrees on the ignition side, Honda chose to employ a hexadecimal numbering system. Let me ask you this: If you saw a 2B cell in a timing map, how would you know what it represents? Simple, it stands for 22 degrees of timing. At least those of you who are electronics wizards are saying that's an easy one. Most of our readers are do-it-yourselfers and are used to the standard stand-alone coding. Rather than reprogramming a Honda ECU, they would take the clearest path and rip out the brain and OEM wiring harness and replace it with a stand alone ECU and universal wiring harness. Remove no more people, because Hondata has "de-scrambled" Honda's hexadecimal system and made programming the Honda ECU a reality-one that won't break the bank.
Rather than wiring in an aftermarket wiring harness, modifications need to be made to the ECU. Hondata provides detailed instructions on installing the necessary parts to open a line of communication with the factory ECU. Tools needed are a soldering iron, solder wick or a solder sucker and solder. The vehicle's ECU determines what hardware needs to be installed.
The Hondata system comes in four different stages from the basic rev limiter removal to a full-blown engine management system complete with data logging capabilities. Stage I consists of removing the rev-limiter and raising speed limiter using a Hondata ROM and ROM socket, as well as an ECU-controlled shift light. No fuel and timing mods are added. Stage II adds a VTEC controller capable of switching the VTEC fuel and timing maps within the ECU using the interface box. Stage III adds a two-step rev limiter for drag launching, which also incorporates the use of the Hondata interface box. The Stage IV brings the ECU to a programmable state via laptop computer. Promoting this unit as a tuning device, we are going to go into the software provided with the Stage IV configuration.
Fuel & Timing
With fuel and timing tables simplified, programming with the Hondata software is identical to programming most stand-alone units. Number values are shown in milliseconds for fuel and actual degrees of timing for timing cells. Unlike most stand-alone units, Hondata allows for calibrating two separate high- and low-speed maps for VTEC-equipped powerplants.
 Modifying the stock ECU consists...  Modifying the stock ECU consists of removing the OEM ROM and replacing it with a ROM socket | 
HC373 chip |  For our application, a four-pin...  For our application, a four-pin interface connector |