if the fuel pressure drops quickly when the engine is shut off, that’s likely the check valve inside the fuel pump is faulty. this can cause a hard start/no start condition when hot as the fuel in the rail boils off. if there is coolant in the cylinders, it may not be bad enough to cause a misfire all the time. recommend a cylinder leak-down test for cooling system leakage, and you may need a pump, too. i wonder what else is wrong, is it still shaking?