It's been wet in Nor-Cal and my 1990 civic si has been presenting issues. When I turn the key I allow for the fuel pump to prime the fuel system before engaging the starter, but this has not been happening. I get one click from the Main Relay and the check engine light comes on; usually the CEL turns off after the fuel pump has been primed, but now it stays on. At first I suspected the relay; I have two relays, a new one and the original, which has been reflowed. Both had been working, and, as it turns out, both are functioning properly.

After testing the relays and checking the fuses I went after the relay harness itself, and that too checked out. While troubleshooting I discovered when the key is left in the on position that the ECU will eventually ground the fuel pump and injectors, and allow for the engine to start. When this first happened I was playing with the harness and falsely believed a short/poor connection was in the harness, but this was not so. I was mislead.

The ECU was the culprit, the capacitors, think of them as little batteries. Over time they fail, they can leak or even explode. In my case their ability to hold electricity is diminishing, therefore, the ECU is compromised. Under normal conditions, when the key is turned, electricity hits the ECU, the capacitors fill and then complete the necessary circuits to start the engine.

Note: it is possible to solder on new capacitors.

Hoping to save the EF community hours of time and frustration, please keep this scenario in mind. Also, besides having a spare Main Relay, it is wise to have a spare ECU, too. And a spare ignitor and or an extra distributor, because these cars are almost 30 years old!

 

interesting.