I have a 1990 civic Si 1.6 5speed stock hatchback. I have been having problems with the vehicle randomly not starting in hot days. I am aware of the possible main relay issue on hot days. I have not replaced it. However, yesterday I was driving on the freeway doing about 65mph when the car just shut off. After stopping I attempted to restart the car. It turns over and was attempting to start but just couldn't. I towed it home and checked the following... -I have spark at the spark plug -I have fuel at the filter -I have fuel to the fuel rail (it passes through the filter) -I used a noid tester to check the wire harness at the injectors, it flashes good -I replaced my timing belt over a year ago. Checked to make sure the belt was not broken. The belt was tight and looked fine. -checked all fuses under dash and under hood. What could be the problem? I felt I should post this because I couldn't find a thread out there that offered other ideas on what to check other then the above things. I towed the vehicle to a local honda dealership for a diagnostic test. I will post what the problem is and hopefully this will help others later on. For now I would like to hear what else I could of checked? Lets see if anyone gets it right before I get the call from the dealership. Things I personally replaced on the vehicle: -clutch and fly wheel -rear engine seal -all engine mounts -both front axels -alternator -battery -timing belt and timing belt tensioner and water pump -oil pan gasket and valve cover gasket -plugs and wires, dizzy cap and rotor -gas tank and straps -radiator -brakes and rotors all around -inner and outer tie rods -possible more I cant think of now! I only list these repair to show I know this car and have repaired a lot and for some reason I can't figure this one out. Its was a sense of defeat when I had to tow it to the dealership.