There have been a few different issues in regards to the Mits/Galant.
Fuel system problems have plagued it, and the ECU had a few issues also.
First, try an old timers method. Remove the intake tube from the intake, and while turning the
engine over, have someone spray(in moderation) starting fluid into the intake.
if it attempts to run, you at least know you don't have an ignition issue.(most likely) This would point signs toward the fuel pump. Fuel pumps do not always give warning of their demise.
If you spray the fluid in, and there is no reaction at all, it is likely to do with the spark control. This is generally associated with the ECM/ECU. Unfortunately, there aren't a huge number of
tests you can run check the spark other than removing one of the wires( with the plug still attached to the sparkplug wire and hold the plug bottom close to a true ground spot while someone turns over the ignition.
Generally, you would see a small spark doing this.
There is on other cause of sudden engine failure here, and it's the least fun of all.
TIMING!!!
Who long has it been since your timing was replaced?
If your timing has failed, this could get pricey.
it is because of the timing system, that the engines spark and fuel ignite and the proper
cycles of the engine.
My advice, try the first two things first. This could eliminate a lot of heartache. and hopefully some of this was
helpful