1991 Regal Ltm. Problem

Ok, so here's the problem: I'm driving my car, everything is going just fine until my RPM gauge drops to about 340, then completely down to zero, killing my engine. I tried starting the engine again, but all it would do is turn over. I left it over night until I could get a tow from my brother, and he checked it out himself the next day. The car started just fine, we drove it back home, where it died as I turned onto my driveway.

Before, my check engine light was on, but I took no real notice of it, since the car was running just fine. In light of recent events, I ran a diagnostic and it threw me a "43" code: knock sensor. I've replaced the knock sensor since then, and took it out for a spin. No engine light, but same problem.

I asked my dad at this point, and he said it could either be the fuel pump or the fuel relay. Not being one with much money, I chose the relay, in hopes that that was the problem. Still no dice.

Before I go out to get a new fuel pump, I wanted to run this by you guys here, in hopes that one of you might have run into this problem before.

Thanks, in advance.

When it dies, check for proper fuel pressure & spark.