I have a 1996 mercury sable and sometimes when I go to start it..it will turn over but it just wont start.

coil or starter. wait.when was last tune up? if never thats the answer

It sounds to me like you need to take out your fuel pump, and get a new one put in. It usually takes about 2 days if you havent done it before. The new fuel pump costs about 100-200 $. You can go to a friend mechanic or a local one. It will probably take them a couple of hours. If you have any further questions contact me.

There are a lot of things that can cause a car not to start so l suggest you have it checked by a good shop before throwing every part in the book at it as you will be told here.

there are too many possibilities to guess

Well l dont know much about newer cars. But you know for sure that your starters working. Maby its your fuel injectors or your idle ajust. or whatever gets your fuel from the gas tank to the fule injectors

How long has it been since u had the fuel filter replaced? Is the check engine light on? The fuel filter is a cheap place to start, if it has not been changed, & they r not hard to do. They have a clip on each end of the fuel filter on ur car.

Look under the hood at the fuel lines coming up from the firewall running to the fuel rail there is a valve stem with possibly a cap on it, take a screwdriver & push the stem in, relieving presure on the fuel system.

The fuel filter is located on the passenger side of the car under the car, below the back seat. An auto parts store carry them & will assist u in purchasing the right one. They r easy to install if u have the area to do so. Take a screw driver & pry the clip out of each end. Gas will run out of the pipe nearest the gas tank so u want to be ready to stick the new filter back on that hose first. Slide the hoses all the way back up on the filter nipples & insert the new clips. When u go to restart ur car, turn the key on & let it sit for 15 seconds to rebuild pressure in ur system.
If ur check engine light is on, then take it to an auto parts store & let them test it on the ODB2 readout machine. They can hook it up & it will let them know what might be going on inside the computer.

One thing that no-one else has mentioned yet, but is very likely is that ur Idle Air Bypass solenoid may need replaced or ur throttle plate may be gummed up. If the problem occurs intermittantly, no ''check engine'' light is on & a check of the OBD-I l system with a code scanner shows no results, then l would definitely go with either or both of these possibilities.

The idle air bypass & the throttle plate both serve to meter the amount of air going into the intake manifold. Combustion byproducts tend to accumulate around where the throttle plate meets the housing & can often result in sudden engine surging, especially at a stop sign. They can be taken care of by purchasing a can of ''Throttle body cleaner'' & following its directions (especially those mentioning safety).

The more likely idea is the Air Bypass Valve. It is a little can looking assembly bolted to the side of the throttle body that has a pair of wires connected to the bottom of it. Its job is to meter the amount of air going by the throttle plate especially under certain conditions (starting, decellerating - esp when suddenly lifting of the accelerator pedal occurs. The cost of replacing it is usually between 50 & 80 USD for the part, including the gasket & labor another 30 - 50 USD