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How to install a Chip on 92-95 OBD-I Honda ECU

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Here is a step by step guide toward installing a racing chip on 1992 to 1995 Honda OBD-I ECUs. First, open up your ECU top cover.


Figure 1
OBD-I USDM and JDM ECUs


Figure 2
Remove Top Cover

  1. Open the top panel of the ECU. Figure 2 is a view of the ECUs Components side. The AT JDM ECU (right) has a  Stock ROM a 28 pins chip with the marking Oki M27256-17 with golden sticker and number 73 no top. It is at the lower left corner away from the ECU Plug (top view, you will have to unscrew the top circuit board P30 only to spot it). As  for the MT JDM ECU there is blank space on the same location marking 27256.
  2. Desolder the stock ROM Figure 3 on the AT JDM ECU like other OBD-0 ECU and solder in place the 28 pin IC socket and plug in the new chip that's just all to easy to chip.
  3. On the MT JDM ECU Figure 3 you will need addition parts to chip these ECU. The first item is a SOP-20 small outline 74HC373 20 pin chip. Fine solder them to the top of the 28 pin IC Socket (red circle). Make sure you don't overheat these small chip and make sure you got the pin 1 in the right position.

Figure 3
Lower left corner of the ECUs
  1. Now you need to bridge the jumper. Figure 4 show the solder side of the ECU. Spot the J1 location in the center of the ECU circuit. Bridge this jumper with SMD 0 ohm resistor or just thin wire. Now you are have just switch the Oki 66207 processor to external memory mode and ready for any racing chip.

    2.  

Figure 4
The J1 jumper on the back of the ECU



 
 
 
 

    Now for Long USDM ECU Like P28, P30 DelSol. Figure 5 shows a P28 ECU being.chipped. First install a 74HC373 chip at upper right corner of the ROM location (optional using 20 pin IC socket). Solder in place the 28 pin IC socket for the new EPROM. Add two capacitors 103 ceramic type in location C51 and C52 (these are optional). Add a 10K ohm resistor in location R54 and jumper on location J1. Now you are ready to plug in the new EPROM.
     
     


    Figure 5
    Chipped P28 ECU




  1. Insert the New Chip or the old stock chip in the 28 pin IC socket.  After that, just reinstall the ECU top and bottom covers. Plug the ECU back on the car, reconnect back the battery positive terminal and start the car to check whether the car is runing fine.If you don't any check light and able to rev pass 4000rpm, you have just successfully chip your ECU.

All Photos are courtesy of Katman - JDMhondaparts.com
©2001 AUTOSERVE
July 28th, 2001