Car cranks but won't start after sitting overnight — 2010 Honda Civic

Classic fuel pressure leak-down. Your fuel system is slowly losing pressure overnight. When you crank in the morning, the pump has to re-pressurize before the engine will fire. Test: Turn the key to ON (not start) for 2 seconds, then OFF, then ON again for 2 seconds. This cycles the fuel pump twice. Then try starting — if it fires right up, you've confirmed the issue. Causes: - Leaking fuel injector (most common) - Weak fuel pump check valve - Bad fuel pressure regulator A fuel pressure gauge left overnight will confirm which side is leaking. Check the [2010 Civic repair guides](/repair/2010/Honda/Civic) for the fuel system pressure test procedure.

Had this on my '09 Civic. It was the fuel pressure regulator on the fuel rail. Honda revised the part. About $45 from RockAuto and 20 minutes to swap.

Also check for any fuel smell near the engine bay in the morning. A leaking injector will sometimes leave a faint gas smell. My '11 had a cracked injector o-ring doing the same thing.