Starter motor Sometimes it starts with no problems but other times it makes a grinding sound and won't start at all. What could be the problem? This is a 1994 ford ranger.

Probably not your battery connections. Always worth a try though. But no need to remove them, just try and twist the connection on the battery terminal. If the wires aren't permanently affixed to the connector, (ie wires bolt to the connector, and connector bolts to the batter)try to move the wires leading into them. If any of the wires move or the connector twists then you need to tighten them. However it is most likely the solenoid in the starter that makes the gear pop out to connect with the fly wheel. If it isn't coming out all the way that's when you hear the gears not properly meshing and grinding against the fly wheel. Take out the starter and bring it with you to the parts store. Not only will Autozone, O'rielys and other big name stores be able to test it, but will ensure you get the correct part if you need a new one. There are also shops that can repair your old starter for a fraction of the cost of a new one, and can usually have it done in an hour or two.

Are you saying the starter is grinding but the engine is not cranking, or the engine is cranking and making noise and not starting ?

You need to have your flywheel: replaced.Your starter motor engages against the fly wheel at the back of the motor. Every time your motor stops it tends to be in the same few positions (just the way things work) so there is more stress on some parts of your fly wheel than others. Because of this the teeth wear out on the fly wheel which means the starter can correctly engage on the fly wheel which is the grinding noise.

Sometimes new starters have to be shimmed so that the gear on the starter lines up with the gear teeth on the flywheel on the motor. The grinding noise is the reason I say that is what's wrong. If there were shims already there, try taking them out. I hope this helps you

check for the starter motor but I suspect a flywheel gear worn. By removing the starter motor would be easier to check the flywheel gear.

This sounds like a damaged starter drive gear and engine flywheel gear.

when replacing a starter motor, some have shims or spacers to make correct distance when installed. if these wre left out on instalation this will cause the problem. another problem can be incorrect number of teeth on starter motor which will cause grinding sound and prevent correct meshing of teeth on flywheel
it is also common to get a bad new starter
check solenoid

Most likely it is your starter. The starter has "teeth" that interlock with "teeth" the turn the engine over and get it started, over time these teeth can wear down causeing the grinding sound you hear. And, until you turn the key a bunch of times and get it so it's on the good teeth, it won't start. That's why it sometimes does and sometimes doesn't.

most likely your bendex wheel in the starter is not engaging the flywheel this could be due to a bad solenoid on the starter. chances are it's a bad starter, i would check to make sure all connections to starter are tight and you have atleast 11.5 -12.5 volts of current in the battery. low voltage can cause this problem as well

remove the starter motor and check for damage/wear on the teeth of the starter motor and the ring gear teeth on the flywheel.turn the engine by hand while checking the ring gear so as to check the condition all the way around.hope this helps