Earlier I was driving a little hard, getting close to 7k rpm, and the rpm sensor went erratic. I slowed down and noticed a knock, and there wasn't as much power. On the way back, the rpm needle occasionally jumped around. Any ideas on what I might have broke? What's the damage?

The engine was rebuilt about 10k miles ago.

 

Bump!

 

Maybe it wasn't rebuilt correctly. Possibly you spun a bearing.

 

I'm still learning about working on engines, please forgive any ignorance.

I tried a cold start and the knock is fairly bad, I don't think one of the cylinders is firing at all. I'm currently stranded about 40 miles from my mechanic, and I'm trying to figure out what to do. I really should have it towed, but I'm thinking I may have to have the engine rebuilt/replaced regardless, so if I can drive it that distance and save myself on towing... (no AAA)

If the RPM sensor is jumping around occasionally, what does that suggest?

Let's say I overfill the oil a little - what is likely to happen if I try driving it home, keeping the RPM really low and taking it easy?

What do you think can be salvaged?

Thanks in advance for advice!