My Hyundai accent would crank but not start once in the morning or after the car has been driven for a while and has been left to cool down for some hours(note: on some rare occasions, it could start one hand)….
But when the car has driven for a long time like an hour plus and is hot, the car would start once...
When the car is cold and refusing to start, if you disconnect the brain box and reconnect it back, the car would start one hand...
What could be the fault of the car?...
Note: A lot of auto electricians have checked the car and have been unable to truly diagnose the fault of the car... Now they just say it's the brain box and I should change it.
Welcome to this forum. This appears to be an electrical problem of some sort.
1. The fuel pump of your vehicle, maybe failing gradually already, and may need to be checked for low fuel pressure problems.
2. If the fuel pressure checked ok, the next thing I'd advice is to inspect the fuel pump relay, if it's also failing.
3. Disconnecting and reconnecting the ECU and the engine cranks and starts, tells me, there could be a partial contact issues with probably the power feed circuit problems between the fuel or ECU relays, or a crankshaft sensor wire harness giving this problem.
4. The problem to the best of my mind, is located within the ECU area, and it's pinout connectors.
5. I'd advice you don't replace the ECU for now.
Wiggle the ECU connector gradually, as you crank the engine.
6. Disconnect one of the spark plug ignition coils, and test for sparks, as you crank the engine. If no spark, have a helper to crank the engine, while someone wiggles the ECU connector. If spark is present while wiggling the harness, and it attempts to start, the problem is some of the harnesses responsible for spark, and engine management, such as crankshaft sensor, is problematic.