One day, the 93 Civic Si failed to start. CEL stayed on and the engine cranked but no start. Left it on the driveway for 2 days. When I went to start it on the third day, the car started on the first attempt. Drove it for about 7 miles, turned it off and tried to start it the next day. It did not start.
Removed the main relay resoldered the joints and reinstalled the relay. Car started after 3 tries. Just in case, bought a new relay and installed it. The car started on the first try. Left the new main relay in the car.
Took it for a drive (about 20 miles). Turned the engine off. When I cam back after an hour, the car would not start. CEL stayed on, no fuel pump sound (The main relay clicked only once. ).
Did the K-test at the MAP sensor and found 5 V. Removed and checked all the fuses both under the hood and under the dash. They are all good. Tried to start the car after these checks. The car did not start.
Removed the ECU and checked for obvious problems. ECU looks good, no obvious discoloration anywhere, no burnt smell. Re installed the ECU.
Was about to leave the car for awhile but decided to try to start. The car started on the first try. The CEL came on, stayed on for a couple of seconds and went off, the fuel pump whirred and the car started.
Drove it for about 20 miles. Next day, it would not start. Main relay clicks once, CEL stays on and no fuel pump noise.
Checked the voltages at the relay. Pin 7 which feeds 12 V to the fuel pump has no voltage. Pin 8 stays at about 11 V, indicating that the ECU is not providing a path to the ground for the fuel pump relay to come on. The ECU ground has been thoroughly cleaned and checked that it makes a good contact.

What signals is the ECU looking for in order to provide the ground path?Any suggestions on what to look for?
(OBD has no stored codes. When the car starts, it runs smoothly with no problems).

. Clean the main ECM ground, located on the thermostat housing.

. Check (or replace) the ignition switch for wear, pitting, or melting.

Your coil is bad you need to change it after three or for tune ups. If you keep on starting it you could burn out the electronic ignition. [email protected]

Regarding 93 civic si's intermittent start problem. The coil checked out fine. In my case, K-test did not indicate that the ECU was bad. After sporadic diagnostics and continued intermittent starts, replaced the ECU. The car came withP28-A01 ECU. Replaced it with P28-A02, (a later revision and is a good replacement). The car has been starting every time for the past week.