Your fuel relay is faulty
car starts but when i put it in gear it stop
It means the car is overheating.
it is 1991 chevolet caprice....ecm
Add oil to your engine and see if it will restart. then take it to the nearest service shop to have the oil leak repaired.
What kind of car year make and model?
Fuel??
The alternator is most likely the problem
fuel pump or crank sensor
Could be a clogged or partially clogged fuel filter, and/or the fuel pump itself. The asker doesn't say whether the car will restart immediately after is stalls or not.
adjust your carb so it will keep the fuel up
It's usually the fuel pump... next time it cuts off bang on the gas tank with a hammer or mag light and see if it starts up. if so it's the fuel pump
Once it cools off it will start.