Replacing ECU capacitors in a 1994 Honda Civic DX
May 2025
The following issue is often discussed in Honda forums about Honda's with OBD1 ECU's: after it rains, the fuel pump does not come on giving a crank/no-start problem. Even if I could stop all the leaks in the windows, doors, under the wiper cowl (I've done them all), humid weather seems to be enough to cause the problem. One possible cause: old, leaking capacitors on the ECU board. At the time of this writing, the ECU in my 1994 hatchback is over 30 years old.
I pulled the ECU to look at the capacitors. The ECU is mounted on the side wall of the passenger compartment behind this carpet.
The carpet can be pulled away by prying up the plastic along the rocker panel. The ECU is secured with 3 10mm bolts and one 10mm nut.
Here it is with the carpet pulled back. I removed the glove box which gave me more room in the tight corner though that is not necessary to remove the ECU.
Two bolts are in the back, one visible in the photo below.
Three cable bundles are plugged into the ECU. They are removed by pushing a small tab on the connector and prying the connector off with a flat blade screwdriver.
Here is the ECU on the operating table.
The screw on the bottom right is quite rusty. I should have soaked it with penetrating oil. Reuslt: I snapped the head of the screw off using a drill driver... Lid off, see the broken screw in the lower right hand corner.
Looks clean and new inside, probably coated with some lacquer or other clear coating. A closer look shows some residue under capacitors 18, 19, 21 and 24. Here is C21 with green crusty stuff underneath.
C18.
I desoldered the bad capacitors with a fine tip on the soldering iron. I had to heat the solder several times while pulling on the capacitors to wiggle the leads out of the holes.
Old and new capacitors. Match the capacitance in uF when replacing the capacitors, the voltage rating can be equal or higher than the original capacitor, but not lower.
I inserted the new capacitor wires into the holes while heating the holes from below, adding fresh solder as necessary. Note that these are electrolytic capacitors with + and - wires. The - wire is labeled with a white line and minus sign. This wire goes into the hole with a minus sign and/or a big white line. The four black upright cylindrical capacitors are the four new ones.
I didn't want to spray some clear protective coating over the new capacitors, decided to seal the ECU with silicone caulk instead. This should help keep moisture and dust out of the case, especially since it is missing a screw...
I struggled to get the ECU bolted in. If I got the front bolt and nut in, I couldn't start the rear bolts. If I started the rear bolts in, I couldn't get the ECU under the bolt heads. Finally, I succeeded by starting the upper rear bolt in and getting the ECU under that bolt. Then I started the front bolt and nut, then I went back and guided the lower rear bolt in with a 3/8" 10mm socket on a long extension. I had to pull the carpet out of the way to get the correct aim on the rear bolt, then I tightened all the bolts and the nut.
The car now starts without hesitation, even after a long rain, as a proper 1994 Honda DX Hatchback should.
Update June 2025
After a week or so, and more wet weather, the car reverted to its old self, crank, no-start. I assume that the car initially behaved itself because the ECU was in a dry environment as I work on it inside at my work bench. I pulled the ECU and searched for problems, found another bad capacitor, C15. See the glob of gunk underneath.
I replaced C15.
While I had the ECU on the bench, I went ahead and replaced C14 even though it looked OK. Here is the original C14, so close to the board that I can't see if there is any gunk underneath.
When I tried to desolder the old capacitor, one of its legs stayed on the board. This didn't happen with any of the other capacitors. Not a healthy sign.
New C14 installed.
I closed up the ECU and installed it in the car. Instant start, no hesitation from the fuel pump. I noticed after a test drive that the car idles more smoothly. Previously, the engine would periodically seek idle, running rough at a stop light. I did not observe that on test drives. I am cautiously optimistic.
June 2025