Arguably, the OBD-1 era ECU’s are the best ECU of all time for Golden Era Honda’s. They are coming up on 30+ years of age and its beginning to show, due to specific symptoms end-user’s can experience. Below are the most common issues. Most of these issues are repairable, and once fixed, can breathe another 20 years of new life into them.
Leaking Capacitors
With these old ECU’s, the capacitors can reach a point where they leak out their inner electrolyte fluid eventually staining the main board which can be potentially damaging. This fluid can also grow a weird turquoise-y mold/fuzz on the legs and/or on the butt of the capacitor. They can also emit a fishy-like smell (if smelt up close or warmed up from de-soldering). They can have a hand in causing the fuel pump to not activate or intermittently activate along with other possible symptoms. They can make the vehicle seem sensitive to atmospheric cold/warm conditions such as no start-ups until after the car is warmed up or when the car is straight cold.
Fuel Pump Issues
If you’ve experienced delayed or straight up no fuel pump priming behavior with your Honda, it can be attributed to bad capacitors and/or bad “IC17” chip. From my experience, the “Integrated Circuit-17 zip” aka “IC17” seems to be more of a culprit than the capacitors in these fuel pump delay issues. The IC17 is part of the power quadrant on the PCB, it manages and regulates certain power functions such as fuel pump operations. Issues like no priming during cold morning temps is almost 99% of the time related to a faulty IC17. I’ve had some customers inform me how they’d perform the Vitamin D trick (which is leaving the ECU in direct sunlight to warm it up) which would speed up the fuel pump delay process (very odd I know, but it works lol). I will say, it’s not a guaranteed a replaced IC17 will bring an ECU back to life but its a worthy start and does most of the time.
Burnt Q31 Transistor
The evap purge control solenoid or PCS (an emissions related solenoid found on the back left side of OBD1 D-series and some B-series intake manifolds) is what the Q31 transistor regulates. Usually, when an engine swap is performed on a 92-00 Civic, it is easy to overlook and mistakenly plug the PCS into the IAT sensor (intake air temp found on the left side intake runner) and vice-verse since they share the same style round 2-wire connector. The voltage for either of these guys are completely different and the result is the burning out of the IAT sensor tip and the Q31 transistor inside the ECU. Sometimes the Q31 can burn out so bad it will damage the board making it impossible to replace. The good thing is it can be removed completely for engine swap purposes if emissions isn’t a priority or required.
Note: Odd as it may seem, the PCS does not throw a CEL when Q31 is burnt out.
