Download Customer Concern: Tests/Procedures: Potential Causes: Tech Tips: Has a misfire on start up only. Sets cylinder #1 misfire code P0301 and cylinder #4 misfire code P0304. Sets pending misfire code P1399 as well. The problem only lasts a few seconds. Suspecting headgasket since the coolant level is low and smells anti-freeze when the engine is started. 1. Check for evidence of anti-freeze on the spark plugs or in the cylinders. Pressure test the cooling system and check for anti-freeze going into the cylinders. 2. If not anti-freeze, check fuel pressure and see if it holds in case a fuel injector is leaking down. 3. If pulling the cylinder head to replace the headgasket, have the cylinder head sent out and checked for cracks. Cylinder Head Cylinder Head Gasket Fuel Injectors Cylinder head was cracked. Other causes of a misfire like spark plug wires and incorrect valve adjustment are common but those wouldn’t likely be a misfire for just a few seconds on cold start up.