Won't start all of a sudden

I have a 91 Civic DX Sedan. I've had it for a little under a year now. For a while, whenever it's around a quarter of a tank or less of gas, it'll stall out whenever I come to a stop, acting like it's completely out of gas. It stops doing this as soon as I put more gas in it. This happens most often after the car has been running for a while, especially after driving on the freeway. Also, occassionally, when I'm out doing errands or something, and I stop somewhere, get back in the car and try to start it, it won't start. The only thing to do when this happens is to sit and wait about five or ten minutes and then the car fires right back up. Doesn't matter the weather, does it warm or cold, but always completely out of nowhere. A few days ago, I get in it to go to school, and it won't start at all. I've tried on and off the past couple of days, and it still won't start. After looking around online, I found out how to find the ECU and get the code off it. It blinks 16 times, which I found through my research means something to do with the fuel injectors, but I have no idea what to do about them or what exactly their problem is. Anyone have any ideas or suggestions for me? I'd appreciate it greatly.

Sounds to me like its your fuel pump. It also could be your main relay but cause of the 1/4 tank of gas thing Im leaning more toward your fuel pump. Also the code 16 can go off when there is no fuel pressure caused by a bad fuel pump and/or main relay.
So tell me this right now how much gas is in the tank? 1/4 tank or less. If yes replace the fuel pump. If theres more fuel in there than when it usually does it I would try replacing the main relay. (under dash, drivers side, directly to the left of your coin tray. Pull the coin tray out 3 screws, One 10mm bolt in the main relay and it comes down)

i agree w/ fuel pump, sounds like it gradually went out.

It's got half a tank. I'll try the main relay. Can I test it with a voltmeter to see if it's really what's causing the problem?

try to listen and see if it is cutting on then off, it should prime when you turn the key on w/ out starting

It's got half a tank. I'll try the main relay. Can I test it with a voltmeter to see if it's really what's causing the problem?

The main relay cant be tested with out power and even if you have power they sometimes test good but there not.
What happens in a main relay is that the contacts on the to relay inside get old and go bad along with the solder joints.
You can fix your by taking a piece of 1000 grit sand paper and sanding down the contact points inside.
BECAREFUL cause the contacts are very small and you could sand away to much. Also you will have to heat all the solder joints up to make sure there all getting good contact.
I have done 2 now and not a single problem. I learned from a shop here locally that takes the bad ones and fixes them and sells them for $20 plus your old one.

try to listen and see if it is cutting on then off, it should prime when you turn the key on w/ out starting

This is not always telling you that it is good. Pump can come on and it still doesnt work the main relay is really screwy on the civic/crxs. i thought that same thing till my Brown DX fired the pump but did not run until I fixed the main relay.

The main relay cant be tested with out power and even if you have power they sometimes test good but there not.
What happens in a main relay is that the contacts on the to relay inside get old and go bad along with the solder joints.
You can fix your by taking a piece of 1000 grit sand paper and sanding down the contact points inside.
BECAREFUL cause the contacts are very small and you could sand away to much. Also you will have to heat all the solder joints up to make sure there all getting good contact.
I have done 2 now and not a single problem. I learned from a shop here locally that takes the bad ones and fixes them and sells them for $20 plus your old one.

Well, I think I may just replace the thing outright since I don't have a soldering iron.

So now for the next question.... The main relay is by the fuse panel, right above the hood release, held in with a bolt, right? I took that out to compare it to one I saw online, and although that's where everyone says you can find the main relay, it didn't look like what they had pictured. The diagrams and pics I've seen show 8 terminals, but the one I pulled only has four, but it comes from exactly where everyone says the main relay should be.

If you pulled the small one thats not it. The one you are looking for is about 3"w x 2"h x 1/2" d. Its against the left wall of the interior. You may have to slightly bend your dash at the bottom also it is easier if you take the bottom 10mm bolt out on the dash. If I had my car here I would take some pics of the area. The one on the left is the one you are looking for. It may or may not have the same Numbers. But its the same thing.

http://i11.ebayimg.com/01/i/03/d3/01/7a_1_b.JPG

If you pulled the small one thats not it. The one you are looking for is about 3"w x 2"h x 1/2" d. Its against the left wall of the interior. You may have to slightly bend your dash at the bottom also it is easier if you take the bottom 10mm bolt out on the dash. If I had my car here I would take some pics of the area. The one on the left is the one you are looking for. It may or may not have the same Numbers. But its the same thing.

I found it. I thought I was going to bust the dash getting the thing out of there, but I got it. Heh. Thanks for your multiple replies and the help!