Mini r50 misfire

[mafotita]

Hello guys
My mini r50 manual transmission 2003 model has cylinder 1 misfire. When I start it , it ideas rough with a flashing engine check light. A few minutes later the light stays on stops flashing. At about that moment it cuts off power supply to cylinder 1 injector. It cannot drive. I continue running for 10-12 minutes and it cuts off the engine. It will not start until the engine is completely cooled down. Now I stuck is this a computer box issue or a head gasket issue ?

More background info

It started boiling when driving below 20 after I changed the radiator. Been doing this for a good 12 months now. Have changed the pressure cap twice, works for a few months then the prob is back again. Then recently it started hesitating when accelerating until it popped the engine check light and stopped driving. I have changed the coil pack after noticing that there was yellow flame instead of blue flame coming from the cyl 1 ht cable. No change with new coil pack! I checking the wiring from the ecu to the injectors, there is continuity. But when I checked power supplies to the injector , which I think should be 12V , cyl 1 injector receives a pulse that lasts about 2-3mins. This apparently coincides with the flashing engine check duration. After that there is no power to cyl 1 at all. And the check light stays on. More intriguing is that when the engine comes on , it comes along with the ASC light and EML as well. Could this be an electrical faulty ?