Socketing and Chipping an OBD0/OBD1 Honda ECU

Verify you have an OBD0 (88-91) or OBD1 (92-95) Honda/Acura engine computer. OBD2 (96-00) units, including a stock OBD2 Accord ECU, cannot be socketed and chipped. Common chippable Civic/Integra part numbers include P06, P28, and P72. A VTEC ECU (for example a P72) can be used on a non-VTEC engine by turning VTEC off in the tuning software, which keeps the same computer usable if you later fit a VTEC head or engine.

Order a socketing/chipping kit from a tuning supplier such as xenocron.com or moates.com. A typical kit includes a 28-pin socket, a 74HC373 latch IC, jumpers, and sometimes replacement capacitors. Assemble a temperature-controlled iron with a new tip, desoldering braid, electronic solder, and flux. A pen-style solder sucker and PCB board wash are useful additions.

Take out the five case screws on each side of the aluminum housing. For clear access, lift the circuit board out of the case entirely: remove the single screw near the connectors that holds the soldered case switch, take off its retaining bar, then undo the six screws on the underside. A bare board is easier to reach on both sides and sheds heat better than one trapped in the case.

Remove only these parts: the 27256 at the EPROM location, the 74HC373, jumper J1, resistor R54, and capacitors C51 and C52. To enable datalogging and real-time tuning, also clear CN2 and jumper J12. Work from the reverse side of the board. Lay the braid flat over a joint and press the iron on top at a shallow angle so the wick touches as much area as possible; the solder is drawn up within a few seconds. A dab of flux makes old solder flow freely. If a hole stays partly filled, add fresh solder and wick it out again, or lift the last of it with the iron tip.

Sustained heat lifts copper pads and traces and can leave the ECU permanently unchippable, so never linger on one joint or one area. Clear the 27256 holes in a scattered order instead of straight across: start at pin 28 (the IC3 marking), move to pin 14, then pin 1, then pin 15, pausing between passes. Touch the board now and then to check the temperature and let it cool if it feels hot.

Fit the 28-pin socket into the 27256 position and mount the 74HC373 latch. The TI latch supplied in many kits needs its pins gently squeezed more parallel so they drop into the board holes. Orient each chip with its notch (half-moon) facing the ECU connector plugs, then solder the pins from the back. Re-flux and reflow any joint that looks dull or starved.

Install a jumper at J1; the J12 jumper you removed can be relocated here. Separately, replace the aging electrolytic capacitor near the middle of the board on the opposite side, adjacent to the harness plugs. It is not part of the chip conversion, just a worn decade-old factory part. It is roughly 2200 uF; match the replacement to the value printed on the original. A different voltage rating is acceptable for this low-voltage circuit (for example a 25 V part in place of the original 35 V).

Wash away flux residue and reseal every spot the iron touched using PCB board wash, which behaves like a carburetor cleaner but is safe for the board. Inspect each reworked joint under good light for cold or bridged connections. Refit the board and reinstall the case screws.

J12 ties the ECU serial port's receive and transmit lines together for the half-duplex under-dash diagnostic connector. Removing it separates those lines so the port runs full-duplex through CN2 for datalogging and real-time programming. In principle this disables the stock diagnostic connector, though many builders report the service connector still works after J12 is cut. To keep it reversible, fit a removable 2-pin jumper header on J12: pull it off to datalog, push it back on to return to stock.

The component list above covers a P28 manual ECU. Other computers need extra parts addressed, for example RM11, Q26, C60, IC14, J10, R67, and D11. Board ID numbers such as 1720, 11F0, and 1980 identify which VTEC conversion kit an ECU takes, so confirm your board before ordering additional parts.