The main reason can absolutely be a blown or cracked headgasket, especially if you already suspect that. Usually the EGR valve is responsible for high NOx, however since your Mitsubishi Galant is emitting white smoke from the exhaust there is a good chance the head gasket is defective. We'd recommend you have a smog check repair station conduct a cylinder wet compression and cylinder dry compression test on all cylinders. This will indicate whether there is a head gasket problem or not.
posted by SmogTips Support
