Engine Performance problem
1990 Other Mitsubishi Models 4 cyl Two Wheel Drive Automatic

i have a 10/1990 starwagon van,auto ,used full tank fuel in 210 ks on hwy,black around tailpipe (too much fuel ?),lost a lot of power,have to keep topping up water ,no water in oil,no leaks dont know what to change first,as would be cheaper to run big block lol,can you help please,also very hard to get up steep hills have to knock down to 1st manualy, will rev good in park,trans level ok,