kobeclutch2494

I did a quick search around and found no real help. my civic starts up fine at first crank. After i turn it off, it will randomly not restart. it cranks but does not start up. as i said it only happens sometimes and when it does im getting spark on all four plugs, i have fuel pressure in the rail it has all new disributor cap and wires and plugs. only thought i have is maybe the injectors arent working but any help would be greatly appreciated!

td1238

When the main relay fails, it cuts both the injectors and the fuel pump. Fuel pressure might still be in the lines from when the fuel pump last worked. In my '90 Civic it'll maintain pressure overnight, so it is possible. If this is the cause, however, and you relieve the pressure, it won't come back until the next time the car starts. If it comes back, then it could be something else besides the main relay. The main relay often fails hot. On my '90 it takes from 1 to 3 minutes for it to cool and work properly again. There are diodes and a resistor within. They can age and fail, or increase in resistance when hot.

When the main relay fails to close on my '90, I get a Code 16. Not sure what yours would be, but probably something pertaining to injectors or fuel supply.

td1238

Just repaired my main relay. Now it starts perfectly every time, even when hot.

The main relay is, as they say, directly above the hood release (in a 1990 DX model). It is a PITA to get at. The plastic panel needs to be loosened and pulled out of the way so that it can just barely squeak through--that is, after the extremely hard to get at 10mm bolt is removed. When I put the relay back, I didn't bother to bolt it in place. I suppose I could later.

The failure on mine was cracked solder connections. I am guessing that this will be the failure for most, if not all. Vibration and heat will fracture the solder connections. The coils are robust, as is the resistor, and the coils don't draw much current, and so it is unlikely that the diodes will become stressed. The resistor is wire-wound and should measure 42 ohms. It is unlikely to drift, but could in rare circumstances open up. The diodes, when checked with the diode check function of a DVM, should measure a forward voltage drop of between .6 and .7 volts. In reverse it should be infinite, or OL. Any numbers in reverse indicate reverse leakage.

Without performing all of these tests, the very least you could do and probably be fine is to remove the cover from the relay by bending the two side tabs. Then reheat all of the solder connections and add more solder to them so that they are good and strong. Then reassemble and be on your way.

The relay contacts can pit and burn, so they could fail at some point. I didn't bother to test mine. Still working well at 265k.