My bottom gears won't work in my 1991 Toyota Celica ST 5 speed

They probely need adjusted but if you bought it new and it started that go back to the dealer have them fix it .

4 speeds were very rare in American models. Tercel, corolla's smaller counterpart came in 4speed manuals but that was to suffice the 12valve motor. Call any Toyota dealer, give them the last 8 of vin and they can verify. Happy holidays.

That's in you gear box. Have a mechanic check it out.

Need the year and the engine type as well as where it was certified for sale.

I had same problem with mine when I first got it. It's really quite a simple fix, if indeed it is the same problem. Anyway you need to jack up the front end and support it on both sides with jack stands. crawl up underneath the car and look for where your gear shifter comes down through the floor of the car. follow the linkage, and check that its nice and tight. I am telling you this from memory so sorry for the vagueness, but there are two pretty big screws holding it in place. Maybe they are lose or as it was in my case, one fell out. I replaced the screw and tightened the other and voila! worked beautifully. Hope this helps.

try the 5th synchronizer ring with splines to rhe rev. gear when engaged

just ram the shifter in your booty,.....duh

starter drive might be bad... fly wheel bad spots poss bad starter you sure its not just clicking???

Grinding going into third gear only may indicate a worn syncronizer ring. There are no adjustments on the shift cables, so I doubt highly that changing the cables will help you, since you are talking about 3rd gear only. Please note: This issue may be still under warranty, if your vehicle has less than 60,000 miles and is not 5 years old. Replacement of 6-speed internal parts is best left to a pro.