There is a big bolt loose at the power steering pump. First thing I saw out of place, but of no consequence to what is causing the noise.
Ask Chris stated, probably bent valve train. You have to check timing with a timing light, or physically check for base timing/timing belt. Something is wrong internal to the engine right now.
We have most manual for Mitsu's located here:
http://www.lilevo.com/mirage/
I suggest a Colt Mirage 89-92 4G15 manual but it may not be needed, you just have to remove the cam cover- the plastic cover not the rocker cover, and check the cam alignment is proper when the crank lines up at TDC marking at the harmonic damper knotch. If things are really rusty on the harmonic, pull a plug (cylinder one or four - closest to cam cover or closest to trans side of motor) and put a long screwdriver driver into the cylinder and crank the motor slowly by hand until the piston gets to it highest, and look at the harmonic markings, and cam alignment points to the head surface. I think most are suspecting the crank jumped a tooth or more. If you have a compression tester, you can just crank the motor with all plugs out and you will know if things are bent - no compression or jumped timing, as opposed to a single cylinder malady.